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I want to make a bunch of identical molds, for 3/4" diameter model
airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? -- http://www.wescottdesign.com |
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On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott
wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
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On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany
wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
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On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote:
On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. -- http://www.wescottdesign.com |
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"Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? -- Ed Huntress |
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On Sat, 9 Apr 2011 00:32:29 -0400, "Ed Huntress"
wrote: "Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Like ED, I'm not picturing your cut. That said, form tools up to 3/8 wide are no trouble on a lathe. For example, I cut a V groove in a pulley for a V belt all the time. This assumes your lathe is rigid enough for the cut. Karl |
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Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? -- http://www.wescottdesign.com Are you referring to a lathe "form tool"? If so that's pretty standard stuff. |
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On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote:
"Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image I'm not so much interested in the flange around the outside as the wheel profile on the inside. Per Pete and Karl I guess I'm looking for a form tool, but one that gets applied in the axial rather than the radial direction. I'm not so interested in cutting the mating flanges -- that's both easy enough and persnickety enough that I should do it by hand. It's getting the tire and hub shapes cut repeatably that interests me. So I guess the real question is: should I be able to do this with a form tool, assuming enough rigidity in my lathe? -- http://www.wescottdesign.com |
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"Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. -- Ed Huntress I'm not so much interested in the flange around the outside as the wheel profile on the inside. Per Pete and Karl I guess I'm looking for a form tool, but one that gets applied in the axial rather than the radial direction. I'm not so interested in cutting the mating flanges -- that's both easy enough and persnickety enough that I should do it by hand. It's getting the tire and hub shapes cut repeatably that interests me. So I guess the real question is: should I be able to do this with a form tool, assuming enough rigidity in my lathe? -- http://www.wescottdesign.com |
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On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote:
"Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. Is this better? http://www.wescottdesign.com/temp/wheel.jpg It's a Smithy lathe, and a form tool is what I was thinking about, except that instead of applying it radially it'd be applied axially -- which means that the ratio of cutting speeds from inside to outside would be huge. I actually sorta-kinda used a forming tool for the tire profile, then cut the hub by hand -- I just want something that'll do a more consistent job of it. -- http://www.wescottdesign.com |
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On 4/9/2011 12:28 PM, Tim Wescott wrote:
So I guess the real question is: should I be able to do this with a form tool, assuming enough rigidity in my lathe? My Dad used to do the inverse of this when making the wheels for wooden toy cars. He ground a form cutter with a tire like profile, mounted it on the arm of a fly cutter in a drill press, cut the profile on one side of the workpiece, flipped the workpiece, cut the profile on the opposite side, then finished cutting the wheel out with a hole saw. I see no reason why you couldn't profile the end of a .75" bar with a form tool. Kevin Gallimore |
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On Apr 8, 10:38*pm, Tim Wescott wrote:
I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? *Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? --http://www.wescottdesign.com A 3/8" wide tool shouldn't be too much for aluminum, if your lathe is solid. I make forming tools to cut round or vee belt grooves in pulleys somewhat narrow and wiggle them in so only the end or one side takes a chip at any instant, reducing the forces and chatter. jsw |
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"Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. Is this better? http://www.wescottdesign.com/temp/wheel.jpg Aha. Yes, that does it. It's a Smithy lathe, and a form tool is what I was thinking about, except that instead of applying it radially it'd be applied axially -- which means that the ratio of cutting speeds from inside to outside would be huge. I actually sorta-kinda used a forming tool for the tire profile, then cut the hub by hand -- I just want something that'll do a more consistent job of it. -- http://www.wescottdesign.com Ok. I get it. Form tools are tricky in a couple of ways. There are basically two types: conventional tools, with a positive rake throughout, and skiving tools, which have zero rake. The former type lead to some very tricky problems of geometry, which would be made much worse by approaching the work axially. They're often held in a special dovetail toolholder. So, to be practical, the thing to try probably is a skiving tool -- a form tool with no top rake. That allows you to use a flat top on the tool that you just cut back for the form, and then cut front clearance and, if necessary, some local side clearance -- either left or right, or both on one tool. This is still a tricky operation, as you can imagine by thinking about what you're trying to accomplish. It's usually done on optical profile grinders or wirecut EDMs. However, I've made little skiving tools, on the order of yours, just by grinding away with a Dremel. I had lots more spare time in those days. The difference in cutting speed across the face would be a problem in steel, but your molds (compression molds?) look like they're aluminum. The only problem there is possible chatter or roughness near the center, made worse by the zero top rake. My experience with facing tells me it could be perfectly Ok. Just keep the tool sharp and lube it with something to enhance surface finish near the center. I'd run the tool pretty fast, because you can get away with a lot using HSS in aluminum, which should help your finish near the center. Form tools usually require some experimenting, anyway. Just try it and see what happens. (Hubbing, sometimes called "hobbing" and described above, is likely to present more problems than form-cutting, IMO.) -- Ed Huntress |
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Why not just get or make a master pattern and then make an epoxy mold
from that? -jim Tim Wescott wrote: On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image I'm not so much interested in the flange around the outside as the wheel profile on the inside. Per Pete and Karl I guess I'm looking for a form tool, but one that gets applied in the axial rather than the radial direction. I'm not so interested in cutting the mating flanges -- that's both easy enough and persnickety enough that I should do it by hand. It's getting the tire and hub shapes cut repeatably that interests me. So I guess the real question is: should I be able to do this with a form tool, assuming enough rigidity in my lathe? -- http://www.wescottdesign.com |
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On 04/09/2011 10:52 AM, jim wrote:
(top posting fixed) Tim Wescott wrote: On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. snip Why not just get or make a master pattern and then make an epoxy mold from that? -jim Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). So I like the idea of using something that's nicely heat conductive. I could look around for a heat conductive epoxy (JB Weld may work, even -- I understand that it's metal filled). But it's hard to beat aluminum for heat conductivity and easy machining (well, brass maybe). And it looks purty. I'm inventing the process, at least as applies to 3-D molding. I may be the 90000th person to do this, but _I_ haven't heard of anyone doing this. I've heard of folks molding Depron sheets around forms, by binding the sheet to the form with Ace bandages, then heating. It's what inspired me to try this -- but this is something that I'm cooking up** out of my own head as I go. * The foam is Depron, which is a close-cell polystyrene foam sold as insulation in Europe, but used for model airplanes the world over. ** Pun not intended, but welcomed with open arms. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
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On 04/09/2011 10:20 AM, Ed Huntress wrote:
"Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. Is this better? http://www.wescottdesign.com/temp/wheel.jpg Aha. Yes, that does it. It's a Smithy lathe, and a form tool is what I was thinking about, except that instead of applying it radially it'd be applied axially -- which means that the ratio of cutting speeds from inside to outside would be huge. I actually sorta-kinda used a forming tool for the tire profile, then cut the hub by hand -- I just want something that'll do a more consistent job of it. -- http://www.wescottdesign.com Ok. I get it. Form tools are tricky in a couple of ways. There are basically two types: conventional tools, with a positive rake throughout, and skiving tools, which have zero rake. The former type lead to some very tricky problems of geometry, which would be made much worse by approaching the work axially. They're often held in a special dovetail toolholder. So, to be practical, the thing to try probably is a skiving tool -- a form tool with no top rake. That allows you to use a flat top on the tool that you just cut back for the form, and then cut front clearance and, if necessary, some local side clearance -- either left or right, or both on one tool. This is still a tricky operation, as you can imagine by thinking about what you're trying to accomplish. It's usually done on optical profile grinders or wirecut EDMs. However, I've made little skiving tools, on the order of yours, just by grinding away with a Dremel. I had lots more spare time in those days. The difference in cutting speed across the face would be a problem in steel, but your molds (compression molds?) look like they're aluminum. The only problem there is possible chatter or roughness near the center, made worse by the zero top rake. My experience with facing tells me it could be perfectly Ok. Just keep the tool sharp and lube it with something to enhance surface finish near the center. I'd run the tool pretty fast, because you can get away with a lot using HSS in aluminum, which should help your finish near the center. Form tools usually require some experimenting, anyway. Just try it and see what happens. (Hubbing, sometimes called "hobbing" and described above, is likely to present more problems than form-cutting, IMO.) Ed: Thank you -- this is just the sort of discussion I was looking for. You forgot to mention that "rake" applies both to the face and the outside edges (I learned that already, as I made a partial tool for the tire portion of this, and had to put rake into it already). I'll give this a whirl, and see how I do. I think I'm going to attempt a conventional tool, as I'm going to have to think backwards and sideways just to get zero rake around the corners, I may as well think a bit skewed as well to get positive rake. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
Duplicate Boring
"Tim Wescott" wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. Is this better? http://www.wescottdesign.com/temp/wheel.jpg Aha. Yes, that does it. It's a Smithy lathe, and a form tool is what I was thinking about, except that instead of applying it radially it'd be applied axially -- which means that the ratio of cutting speeds from inside to outside would be huge. I actually sorta-kinda used a forming tool for the tire profile, then cut the hub by hand -- I just want something that'll do a more consistent job of it. -- http://www.wescottdesign.com Ok. I get it. Form tools are tricky in a couple of ways. There are basically two types: conventional tools, with a positive rake throughout, and skiving tools, which have zero rake. The former type lead to some very tricky problems of geometry, which would be made much worse by approaching the work axially. They're often held in a special dovetail toolholder. So, to be practical, the thing to try probably is a skiving tool -- a form tool with no top rake. That allows you to use a flat top on the tool that you just cut back for the form, and then cut front clearance and, if necessary, some local side clearance -- either left or right, or both on one tool. This is still a tricky operation, as you can imagine by thinking about what you're trying to accomplish. It's usually done on optical profile grinders or wirecut EDMs. However, I've made little skiving tools, on the order of yours, just by grinding away with a Dremel. I had lots more spare time in those days. The difference in cutting speed across the face would be a problem in steel, but your molds (compression molds?) look like they're aluminum. The only problem there is possible chatter or roughness near the center, made worse by the zero top rake. My experience with facing tells me it could be perfectly Ok. Just keep the tool sharp and lube it with something to enhance surface finish near the center. I'd run the tool pretty fast, because you can get away with a lot using HSS in aluminum, which should help your finish near the center. Form tools usually require some experimenting, anyway. Just try it and see what happens. (Hubbing, sometimes called "hobbing" and described above, is likely to present more problems than form-cutting, IMO.) Ed: Thank you -- this is just the sort of discussion I was looking for. You forgot to mention that "rake" applies both to the face and the outside edges (I learned that already, as I made a partial tool for the tire portion of this, and had to put rake into it already). Well, if you're plunging the tool straight in, the rake (if any) is on the top of the tool, and the relief, for clearance, is on the front and, theoretically, both sides. But real-world skiving tools typically have no side clearance. The side clearance appears automatically as a result of front clearance and angles in the shape you're cutting. But sometimes not. It depends on the geometry of the cut. You can think through it. Watch for decreasing clearance on the outside of the tool, due to the radius of the workpiece. I'll give this a whirl, and see how I do. I think I'm going to attempt a conventional tool, as I'm going to have to think backwards and sideways just to get zero rake around the corners, I may as well think a bit skewed as well to get positive rake. Good luck. You can project the finished workpiece shape onto the top of the tool, with rake, by using a CAD program. Watch out for the effectively changing center height as you plunge the tool, if you choose to use top rake. It's like patting your head while rubbing your stomach. g -- Ed Huntress -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
Duplicate Boring
On 04/09/2011 02:19 PM, Ed Huntress wrote:
"Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. Is this better? http://www.wescottdesign.com/temp/wheel.jpg Aha. Yes, that does it. It's a Smithy lathe, and a form tool is what I was thinking about, except that instead of applying it radially it'd be applied axially -- which means that the ratio of cutting speeds from inside to outside would be huge. I actually sorta-kinda used a forming tool for the tire profile, then cut the hub by hand -- I just want something that'll do a more consistent job of it. -- http://www.wescottdesign.com Ok. I get it. Form tools are tricky in a couple of ways. There are basically two types: conventional tools, with a positive rake throughout, and skiving tools, which have zero rake. The former type lead to some very tricky problems of geometry, which would be made much worse by approaching the work axially. They're often held in a special dovetail toolholder. So, to be practical, the thing to try probably is a skiving tool -- a form tool with no top rake. That allows you to use a flat top on the tool that you just cut back for the form, and then cut front clearance and, if necessary, some local side clearance -- either left or right, or both on one tool. This is still a tricky operation, as you can imagine by thinking about what you're trying to accomplish. It's usually done on optical profile grinders or wirecut EDMs. However, I've made little skiving tools, on the order of yours, just by grinding away with a Dremel. I had lots more spare time in those days. The difference in cutting speed across the face would be a problem in steel, but your molds (compression molds?) look like they're aluminum. The only problem there is possible chatter or roughness near the center, made worse by the zero top rake. My experience with facing tells me it could be perfectly Ok. Just keep the tool sharp and lube it with something to enhance surface finish near the center. I'd run the tool pretty fast, because you can get away with a lot using HSS in aluminum, which should help your finish near the center. Form tools usually require some experimenting, anyway. Just try it and see what happens. (Hubbing, sometimes called "hobbing" and described above, is likely to present more problems than form-cutting, IMO.) Ed: Thank you -- this is just the sort of discussion I was looking for. You forgot to mention that "rake" applies both to the face and the outside edges (I learned that already, as I made a partial tool for the tire portion of this, and had to put rake into it already). Well, if you're plunging the tool straight in, the rake (if any) is on the top of the tool, and the relief, for clearance, is on the front and, theoretically, both sides. But real-world skiving tools typically have no side clearance. The side clearance appears automatically as a result of front clearance and angles in the shape you're cutting. But sometimes not. It depends on the geometry of the cut. You can think through it. Watch for decreasing clearance on the outside of the tool, due to the radius of the workpiece. I'll give this a whirl, and see how I do. I think I'm going to attempt a conventional tool, as I'm going to have to think backwards and sideways just to get zero rake around the corners, I may as well think a bit skewed as well to get positive rake. Good luck. You can project the finished workpiece shape onto the top of the tool, with rake, by using a CAD program. Watch out for the effectively changing center height as you plunge the tool, if you choose to use top rake. It's like patting your head while rubbing your stomach.g Whoops -- I was seeing "rake" and thinking "clearance". Skiving is probably the right way to go, unless I _really_ want to get busy with the dremel tool. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
Duplicate Boring
"Tim Wescott" wrote in message ... On 04/09/2011 02:19 PM, Ed Huntress wrote: "Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Hobbing? P.S. Not the gear-making process, this one: http://tinyurl.com/hobbing Well, the cavity is cylindrically symmetrical, so I'm not sure that "hobbing" is the right term. It's probably been a screw machine operation since 1920, or at least some sort of tracing operation. Sigh -- I'm always behind the curve. I must be dull tonight, but I can't visualize what you're doing. Are you talking about some kind of forming in the axis of a spinning tube, or turning the outside diameter to a profile? Let me know if you can see this, it should explain: http://www.hippocketaeronautics.com/...rum/index.php? action=dlattach;topic=5869.0;attach=53766;image Sorry, that isn't working for me. Or I don't know how to get there. I'll wait and see what others come up with. It sounds like you want to do some kind of form-tool operation, in which case, as someone mentioned, the key is the length of contact for the cutting edge. I've seen some really long ones -- the whole length of a chess piece, for example -- performed on South Bend 10" lathes with complete success. But I may be on the wrong track. I'll wait. Is this better? http://www.wescottdesign.com/temp/wheel.jpg Aha. Yes, that does it. It's a Smithy lathe, and a form tool is what I was thinking about, except that instead of applying it radially it'd be applied axially -- which means that the ratio of cutting speeds from inside to outside would be huge. I actually sorta-kinda used a forming tool for the tire profile, then cut the hub by hand -- I just want something that'll do a more consistent job of it. -- http://www.wescottdesign.com Ok. I get it. Form tools are tricky in a couple of ways. There are basically two types: conventional tools, with a positive rake throughout, and skiving tools, which have zero rake. The former type lead to some very tricky problems of geometry, which would be made much worse by approaching the work axially. They're often held in a special dovetail toolholder. So, to be practical, the thing to try probably is a skiving tool -- a form tool with no top rake. That allows you to use a flat top on the tool that you just cut back for the form, and then cut front clearance and, if necessary, some local side clearance -- either left or right, or both on one tool. This is still a tricky operation, as you can imagine by thinking about what you're trying to accomplish. It's usually done on optical profile grinders or wirecut EDMs. However, I've made little skiving tools, on the order of yours, just by grinding away with a Dremel. I had lots more spare time in those days. The difference in cutting speed across the face would be a problem in steel, but your molds (compression molds?) look like they're aluminum. The only problem there is possible chatter or roughness near the center, made worse by the zero top rake. My experience with facing tells me it could be perfectly Ok. Just keep the tool sharp and lube it with something to enhance surface finish near the center. I'd run the tool pretty fast, because you can get away with a lot using HSS in aluminum, which should help your finish near the center. Form tools usually require some experimenting, anyway. Just try it and see what happens. (Hubbing, sometimes called "hobbing" and described above, is likely to present more problems than form-cutting, IMO.) Ed: Thank you -- this is just the sort of discussion I was looking for. You forgot to mention that "rake" applies both to the face and the outside edges (I learned that already, as I made a partial tool for the tire portion of this, and had to put rake into it already). Well, if you're plunging the tool straight in, the rake (if any) is on the top of the tool, and the relief, for clearance, is on the front and, theoretically, both sides. But real-world skiving tools typically have no side clearance. The side clearance appears automatically as a result of front clearance and angles in the shape you're cutting. But sometimes not. It depends on the geometry of the cut. You can think through it. Watch for decreasing clearance on the outside of the tool, due to the radius of the workpiece. I'll give this a whirl, and see how I do. I think I'm going to attempt a conventional tool, as I'm going to have to think backwards and sideways just to get zero rake around the corners, I may as well think a bit skewed as well to get positive rake. Good luck. You can project the finished workpiece shape onto the top of the tool, with rake, by using a CAD program. Watch out for the effectively changing center height as you plunge the tool, if you choose to use top rake. It's like patting your head while rubbing your stomach.g Whoops -- I was seeing "rake" and thinking "clearance". Skiving is probably the right way to go, unless I _really_ want to get busy with the dremel tool. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Yes, keep it as simple as you can. Don't forget that the workpiece radius will take care of clearance on the inside-facing features of the tool, but you'll need extra clearance on the outside-facing features, because of the radius of the workpiece. Making these tools is almost a lost art, although dovetail form tools with top rake are still common in production. With CAD and a CNC wirecut EDM or CNC/optical profile grinder, the whole process of making them in simpler in commercial toolmaking. But you can make perfectly good skiving tools by hand. -- Ed Huntress |
Duplicate Boring
"Tim Wescott" wrote in message ... On 04/09/2011 02:19 PM, Ed Huntress wrote: "Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Since you got me started on this, g here are two other things to consider. First, on regular skiving tools, which plunge in from the side of the work, it's common when cutting steel to set the top of the tool 0.002" or so above the centerline to get some effective top rake, or, more commonly, 0.002" *below* the centerline, to avoid the need, in shallow cuts, for front clearance. When wire EDM first came on the market, a lot of tools were made this way, because you couldn't tilt the wire on those early ones. They just left them square on the ends, with no clearance. This probably means little when cutting aluminum and plunging from the end is no place to try it, anyway. But if you like working with these tools and try them from the side, particularly on steel, keep it in mind. The other point, about your workpiece material: It looks like you're machining wrought barstock, probably 6061 or 2024. I don't know the figures for 6061 but in 2024, the thermal conductivity in the T3 or T4 state is roughly half that of the same material in the annealed state. I'm sure you won't be annealing the material just from heating the foam, but if you have in mind to anneal the tool first, to get better conductivity, keep in mind that the material will revert to the tempered state in a couple of hours if you don't give it a full anneal. Neither of things probably matter, but I hate to leave details hanging around, just in case. d8-) -- Ed Huntress |
Duplicate Boring
On Sat, 09 Apr 2011 18:27:27 -0400, Ed Huntress wrote:
"Tim Wescott" wrote in message ... On 04/09/2011 02:19 PM, Ed Huntress wrote: "Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Since you got me started on this, g here are two other things to consider. The other point, about your workpiece material: It looks like you're machining wrought barstock, probably 6061 or 2024. I don't know the figures for 6061 but in 2024, the thermal conductivity in the T3 or T4 state is roughly half that of the same material in the annealed state. I'm sure you won't be annealing the material just from heating the foam, but if you have in mind to anneal the tool first, to get better conductivity, keep in mind that the material will revert to the tempered state in a couple of hours if you don't give it a full anneal. Neither of things probably matter, but I hate to leave details hanging around, just in case. d8-) It is, indeed, 6061, heat treated to some three or four-digit code with a "T6" at the beginning. So I'm assuming that for my purposes it's T6. I'm mostly thinking of heat conductivity in competition with plastic or wood. Since the current process involves clamping up one mold with a pair of vice grips and tossing the assembly in the oven for half an hour, I can't claim that speed is of the essence. Before I start worrying about the thermal conductivity of the aluminum I should think about better ways to conduct heat _to_ the aluminum, like fins and a fan in the oven, or immersing the mold in boiling water, instead of putting it in a still-air oven. I'm still tickled that I can make a wheel for a 7-gram rubber power plane that barely registers on my 100mg-per-step scale -- it'll take me a while to get past that. -- http://www.wescottdesign.com |
Duplicate Boring
"Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 18:27:27 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On 04/09/2011 02:19 PM, Ed Huntress wrote: "Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Since you got me started on this, g here are two other things to consider. The other point, about your workpiece material: It looks like you're machining wrought barstock, probably 6061 or 2024. I don't know the figures for 6061 but in 2024, the thermal conductivity in the T3 or T4 state is roughly half that of the same material in the annealed state. I'm sure you won't be annealing the material just from heating the foam, but if you have in mind to anneal the tool first, to get better conductivity, keep in mind that the material will revert to the tempered state in a couple of hours if you don't give it a full anneal. Neither of things probably matter, but I hate to leave details hanging around, just in case. d8-) It is, indeed, 6061, heat treated to some three or four-digit code with a "T6" at the beginning. So I'm assuming that for my purposes it's T6. Yes. The other codes have meaning, but they aren't relevant here. I'm mostly thinking of heat conductivity in competition with plastic or wood. Since the current process involves clamping up one mold with a pair of vice grips and tossing the assembly in the oven for half an hour, I can't claim that speed is of the essence. Before I start worrying about the thermal conductivity of the aluminum I should think about better ways to conduct heat _to_ the aluminum, like fins and a fan in the oven, or immersing the mold in boiling water, instead of putting it in a still-air oven. How hot does it have to be? I'm still tickled that I can make a wheel for a 7-gram rubber power plane that barely registers on my 100mg-per-step scale -- it'll take me a while to get past that. That's very cool. Do you know who Bob Hatschek is? (Or have you heard of the Hatschek Hook?) He held some free-flight glider records at one time, and he got me interested in indoor rubber. I made some with film-covered wings about 20 years ago but it was only a passing interest. The Hatschek Hook, which was a towline release hook for competition gliders, and which Bob sold worldwide, is the only product I ever knew of that was made exclusively on a Unimat. g Bob was an editor at _American Machinist_ in its glory days. -- Ed Huntress -- http://www.wescottdesign.com |
Duplicate Boring
On Sat, 09 Apr 2011 22:39:06 -0400, Ed Huntress wrote:
"Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 18:27:27 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On 04/09/2011 02:19 PM, Ed Huntress wrote: "Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Since you got me started on this, g here are two other things to consider. The other point, about your workpiece material: It looks like you're machining wrought barstock, probably 6061 or 2024. I don't know the figures for 6061 but in 2024, the thermal conductivity in the T3 or T4 state is roughly half that of the same material in the annealed state. I'm sure you won't be annealing the material just from heating the foam, but if you have in mind to anneal the tool first, to get better conductivity, keep in mind that the material will revert to the tempered state in a couple of hours if you don't give it a full anneal. Neither of things probably matter, but I hate to leave details hanging around, just in case. d8-) It is, indeed, 6061, heat treated to some three or four-digit code with a "T6" at the beginning. So I'm assuming that for my purposes it's T6. Yes. The other codes have meaning, but they aren't relevant here. I'm mostly thinking of heat conductivity in competition with plastic or wood. Since the current process involves clamping up one mold with a pair of vice grips and tossing the assembly in the oven for half an hour, I can't claim that speed is of the essence. Before I start worrying about the thermal conductivity of the aluminum I should think about better ways to conduct heat _to_ the aluminum, like fins and a fan in the oven, or immersing the mold in boiling water, instead of putting it in a still-air oven. How hot does it have to be? Damned if I know. I _do_ know that if I bake it for 30 minutes at 150 degrees it forms, but doesn't seem to do so as well. If I bake it for 30 minutes at 200, it works better. I should try 250 -- I expect I'll melt the plastic, but that'll be a learning experience, right? -- http://www.wescottdesign.com |
Duplicate Boring
"Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 22:39:06 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On Sat, 09 Apr 2011 18:27:27 -0400, Ed Huntress wrote: "Tim Wescott" wrote in message ... On 04/09/2011 02:19 PM, Ed Huntress wrote: "Tim wrote in message ... On 04/09/2011 10:20 AM, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote: "Tim wrote in message ... On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote: "Tim wrote in message ... On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany wrote: On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott wrote: I want to make a bunch of identical molds, for 3/4" diameter model airplane wheels. I'm envisioning a tool that's 3/8" across, that I just sharpen up, grit my teeth, and push into a spinning piece of aluminum to make my desired profile. Is this a sensible thing to consider? Is there some other way (short of CNC machining) to easily duplicate cavities in the ends of a bunch of aluminum tubes? Since you got me started on this, g here are two other things to consider. The other point, about your workpiece material: It looks like you're machining wrought barstock, probably 6061 or 2024. I don't know the figures for 6061 but in 2024, the thermal conductivity in the T3 or T4 state is roughly half that of the same material in the annealed state. I'm sure you won't be annealing the material just from heating the foam, but if you have in mind to anneal the tool first, to get better conductivity, keep in mind that the material will revert to the tempered state in a couple of hours if you don't give it a full anneal. Neither of things probably matter, but I hate to leave details hanging around, just in case. d8-) It is, indeed, 6061, heat treated to some three or four-digit code with a "T6" at the beginning. So I'm assuming that for my purposes it's T6. Yes. The other codes have meaning, but they aren't relevant here. I'm mostly thinking of heat conductivity in competition with plastic or wood. Since the current process involves clamping up one mold with a pair of vice grips and tossing the assembly in the oven for half an hour, I can't claim that speed is of the essence. Before I start worrying about the thermal conductivity of the aluminum I should think about better ways to conduct heat _to_ the aluminum, like fins and a fan in the oven, or immersing the mold in boiling water, instead of putting it in a still-air oven. How hot does it have to be? Damned if I know. I _do_ know that if I bake it for 30 minutes at 150 degrees it forms, but doesn't seem to do so as well. If I bake it for 30 minutes at 200, it works better. I should try 250 -- I expect I'll melt the plastic, but that'll be a learning experience, right? Yeah, it sounds like it's the right time for some experiments. And if the right temperature turns out to be 212 F, you may have a couple of problems solved at once. -- Ed Huntress -- http://www.wescottdesign.com |
Duplicate Boring
On Sat, 09 Apr 2011 13:47:57 -0700, Tim Wescott
wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Take care. Good Luck. Brian Lawson, Bothwell, Ontario. |
Duplicate Boring
On 04/10/2011 03:19 PM, Brian Lawson wrote:
On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits & bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
Duplicate Boring
On Mon, 11 Apr 2011 09:53:05 -0700, Tim Wescott
wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits & bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. The only blow molding I'm familiar with is for extremely high production of containers like milk bottles, shampoo bottles, etc. A parison is extruded, clamped in the mold, then the parison is blown against the mold with air. Usually a bunch of molds are arranged on a wheel or other contraption, and open and close around the parisons automatically. Spits out containers at a high rate. There may be a lab analog of this process for testing, don't know. Foam sheet is turned into cups in thermoforming machines. Large plastic sheets are shaped into various objects via vacuum forming. There are hobbyist versions of that process. Other processes include rotomolding (large tanks), injection molding (solid parts), injection blow molding, injection stretch blow molding, etc. Pete Keillor Pete Keillor |
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On Mon, 11 Apr 2011 09:53:05 -0700, Tim Wescott
wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits & bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". |
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On 04/11/2011 10:14 AM, Spehro Pefhany wrote:
On Mon, 11 Apr 2011 09:53:05 -0700, Tim wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits& bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. So what do you call molding with styrofoam beads? * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
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On Mon, 11 Apr 2011 11:26:15 -0700, Tim Wescott
wrote: So what do you call molding with styrofoam beads? EPS (Expanded Poly Styrene) molding. I looked into setting up a line once, and it was too much hassle- required a boiler to heat the beads etc., but I think this process might actually be possible on a table top using your aluminum molds. Worth looking into. Alternatively maybe some kind of reaction molding (RIM) that leaves the wheels full of bubbles but with a tough skin. Getting the materials in sensible quantities for you could be a challenge. * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. |
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"Tim Wescott" wrote in message ... On 04/11/2011 10:14 AM, Spehro Pefhany wrote: On Mon, 11 Apr 2011 09:53:05 -0700, Tim wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits& bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. As others have said, blow molding is a process carried out with solid resins in a semi-liquid state. I've never heard of anything that small being blow molded, nor have I heard of doing it with styrene beads, but technology marches on and I mostly don't. So what do you call molding with styrofoam beads? Molding polystyrene beads. g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, and it's close-cell material. Molding the beads produces a porous material.) Molding polystyrene beads is done by filling a mold with them and then injecting steam or hot air. I don't think you want to go there. -- Ed Huntress * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
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Ed Huntress wrote:
"Tim Wescott" wrote in message ... On 04/11/2011 10:14 AM, Spehro Pefhany wrote: On Mon, 11 Apr 2011 09:53:05 -0700, Tim wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits& bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. As others have said, blow molding is a process carried out with solid resins in a semi-liquid state. I've never heard of anything that small being blow molded, nor have I heard of doing it with styrene beads, but technology marches on and I mostly don't. So what do you call molding with styrofoam beads? Molding polystyrene beads. g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, and it's close-cell material. Molding the beads produces a porous material.) Molding polystyrene beads is done by filling a mold with them and then injecting steam or hot air. I don't think you want to go there. * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. -- Tim Wescott what about rotational molding? that's usually done with powder, and the wheels would be hollow when done. |
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"chaniarts" wrote in message ... Ed Huntress wrote: "Tim Wescott" wrote in message ... On 04/11/2011 10:14 AM, Spehro Pefhany wrote: On Mon, 11 Apr 2011 09:53:05 -0700, Tim wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits& bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. As others have said, blow molding is a process carried out with solid resins in a semi-liquid state. I've never heard of anything that small being blow molded, nor have I heard of doing it with styrene beads, but technology marches on and I mostly don't. So what do you call molding with styrofoam beads? Molding polystyrene beads. g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, and it's close-cell material. Molding the beads produces a porous material.) Molding polystyrene beads is done by filling a mold with them and then injecting steam or hot air. I don't think you want to go there. * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. -- Tim Wescott what about rotational molding? that's usually done with powder, and the wheels would be hollow when done. That's for things like industrial drums and plastic kayaks. I don't think you'd have much luck in such small sizes. If it were me, the first thing I'd try is pressing the wheels out of Styrofoam (closed-cell) or beadboard (open-cell) with hot mold halves. It doesn't take a lot of heat to make polystyrene pliable. You'd have maximum density at the wheel tread, and a bit of skin on the outside. You probably could get away with a low-density polystyrene foam. -- Ed Huntress |
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"Ed Huntress" wrote in message ... "chaniarts" wrote in message ... Ed Huntress wrote: "Tim Wescott" wrote in message ... On 04/11/2011 10:14 AM, Spehro Pefhany wrote: On Mon, 11 Apr 2011 09:53:05 -0700, Tim wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits& bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. As others have said, blow molding is a process carried out with solid resins in a semi-liquid state. I've never heard of anything that small being blow molded, nor have I heard of doing it with styrene beads, but technology marches on and I mostly don't. So what do you call molding with styrofoam beads? Molding polystyrene beads. g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, and it's close-cell material. Molding the beads produces a porous material.) Molding polystyrene beads is done by filling a mold with them and then injecting steam or hot air. I don't think you want to go there. * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. -- Tim Wescott what about rotational molding? that's usually done with powder, and the wheels would be hollow when done. That's for things like industrial drums and plastic kayaks. I don't think you'd have much luck in such small sizes. If it were me, the first thing I'd try is pressing the wheels out of Styrofoam (closed-cell) or beadboard (open-cell) with hot mold halves. It doesn't take a lot of heat to make polystyrene pliable. You'd have maximum density at the wheel tread, and a bit of skin on the outside. You probably could get away with a low-density polystyrene foam. Correction, to avoid confusion: Beadboard, and other products made from compacted polystyrene beads (such as coffee cups), are *not* open-cell. The finished product usually is somewhat porous, but the beads themselves are closed-cell. Styrofoam is extruded, close-cell foam, and it's not made from compacted beads. Also BTW: you might need some mold release on those mold halves if you're going to trying heating them and pressing the wheels out of sheet. PVA (polyvinyl alcohol, available at boat-repair supply places and craft shops) might be the right thing. It's used as the primary release agent for polyester resin, which is loaded with styrene monomer. But considering that the pressed sheet won't be liquefied, vaseline petroleum jelly -- Ed Huntress |
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On 4/11/2011 2:40 PM, Ed Huntress wrote:
Molding polystyrene beads.g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, You may be looking for the word "Extruded". Kevin Gallimore |
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"axolotl" wrote in message ... On 4/11/2011 2:40 PM, Ed Huntress wrote: Molding polystyrene beads.g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, You may be looking for the word "Extruded". Kevin Gallimore Styrofoam is indeed extruded, but the generic definition for EPF is "expanded." Extruded foam was expanded in the process of making it. You'll see both definitions for EPF in the industry literature. -- Ed Huntress |
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On 04/11/2011 11:49 AM, Ed Huntress wrote:
wrote in message ... Ed Huntress wrote: "Tim wrote in message ... On 04/11/2011 10:14 AM, Spehro Pefhany wrote: On Mon, 11 Apr 2011 09:53:05 -0700, Tim wrote: On 04/10/2011 03:19 PM, Brian Lawson wrote: On Sat, 09 Apr 2011 13:47:57 -0700, Tim wrote: SNIP Because the process is to put a flat piece of foam in the mold, clamp it, then chuck it in an oven to heat. The foam* softens and expands to meet the edges of the mold. Then you take it out of the oven and let it cool, and voile! A part (or a mess -- it's best to enter any sort of casting process with your eyes open). SNIP I've never done it, but it reads like what you want to do would be achieved with blow molding. You could even put "tread" on the tire then. Interesting thought. Probably beyond the sophistication I was aiming for (mostly hand tools, with bits& bobs turned on the lathe). And I think blow molding is for styrofoam beads, which isn't what Depron is. I'm not sure that I've seen styrofoam beads that are small enough for a wheel that's 3/16" thick and 3/4" diameter. Blow molding is what is used to make plastic bottles. Basically a thick plastic goober* is extruded vertically (the plastic has to be of a type that has a viscosity high enough that it doesn't drool off the nozzle). The mold clamps around the parison (sealing off the bottom end) and then it's inflated with compressed air through the top. After it cools a bit, a nice sharp knife called a moil** slices off a bit at the top (usually the top of the neck where the closure goes), the mold opens and the bottle falls out. The tab at the bottom is stripped off automatically or manually. I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. * It's called a "parison", a term borrowed from a French term "paraison", relating to glass blowing. ** not joking, that's what it's called-- at least it's not spelled "mohel". Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. As others have said, blow molding is a process carried out with solid resins in a semi-liquid state. I've never heard of anything that small being blow molded, nor have I heard of doing it with styrene beads, but technology marches on and I mostly don't. So what do you call molding with styrofoam beads? Molding polystyrene beads.g (Styrofoam is a trademark name for EPF -- expanded polystyrene foam, and it's close-cell material. Molding the beads produces a porous material.) Molding polystyrene beads is done by filling a mold with them and then injecting steam or hot air. I don't think you want to go there. * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. -- Tim Wescott what about rotational molding? that's usually done with powder, and the wheels would be hollow when done. That's for things like industrial drums and plastic kayaks. I don't think you'd have much luck in such small sizes. If it were me, the first thing I'd try is pressing the wheels out of Styrofoam (closed-cell) or beadboard (open-cell) with hot mold halves. It doesn't take a lot of heat to make polystyrene pliable. You'd have maximum density at the wheel tread, and a bit of skin on the outside. You probably could get away with a low-density polystyrene foam. Right now I'm cold-pressing, and then heating. I'm not sure if I want to go to the trouble of hot-pressing -- but, maybe it's the way to go. Hmm. More complications... (And there's no sign of the product sticking to the mold). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |
Duplicate Boring
On Mon, 11 Apr 2011 11:26:15 -0700, Tim Wescott
wrote: big snip Ah -- that wouldn't work, and once again I'm confused in my terminology. The application is very weight-sensitive: indoor rubber power competition rules call out a seven gram minimum weight for this sort of plane*, and that minimum is _very_ hard to build down to. I've got a pair of wheels that look injection molded, but have about the same wall width as most of the blow molded things I've seen. They weigh in at 600mg for the pair, while my wheels weigh in at less than 100mg each. So what do you call molding with styrofoam beads? * AFAIK, just about anything with wheels and a minimum weight calls out 7 grams -- 14 grams for outdoor. I think vacuum forming might give you something useful for relatively light weight. Heat up a sheet of something formable clamped in a frame via IR (think toaster oven), pull it out, place it over two male half molds, suck down. Cut out halves and glue together when cool. On the other hand, it probably won't be as light as some rims bent up and glued out of graphite prepreg tape, with graphite spokes and graphite tube hub (maybe cure in the same toaster oven). If your target complete model weight is 7 grams, anything molded will be pretty heavy by comparison. Pete Keillor |
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Spehro Pefhany wrote:
I don't know how you'd do this without a rather complex machine- but the molds are relatively easy because the pressures are very low by molding standards. It might be "complex," but it doesn't necessarily have to be "big" - Many years ago, there was an amusement park in Excelsior, MN, with a way kewl wood coaster, fun house, arcade, and all that other fun amusement park stuff that's illegal today because it's too dangerous for our oh-so- fragile little darlings. One of the things in the arcade was a box no bigger than a jukebox, that for a quarter would blow-mold a little plastic unicorn shelf knick-knack right before your very eyes. It would close the mold, shoot the goo, run cooling water through the mold, open the mold, and scrape the little unicorn off the platen down into the pick-up bin. I'd think the only "complex" part would be figuring out the right temperatures and pressures for the molding process itself - the rest is just sequencing. :-) I once made a process sequencer with a stack of garolite cams that I cut on the rotary cable, and a bank of industrial-grade microswitches. :-) Cheers! Rich |
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Tim Wescott wrote:
So what do you call molding with styrofoam beads? I dunno, but do they have that in an aerosol form, like that expanding urethane stuff? Good Luck! Rich |
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