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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Lathe Suggestions
A follow rest mounted on a sturdy tripod maybe?
Just brainstorming. |
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Lathe Suggestions
There are at least three points to deal with. You have to support the
weight of the shaft, you need to keep it straight, and you need to deal with the critical speed. The first two are trivial. By the way, I assume this is an axial stick-out for a through-hole spindle, not a radial stick-out. If you have a 10' radial stick-out you have a serious problem. But the critical speed issue is also a serious problem. If you are getting withing 10% of critical speed you will need to do some real engineering. I envision lots of pillow blocks on a long piece of large box tubing. "Rob Hammond" wrote in message ... Hi all What products / ideas exist that will support a long bar (say 10 ft) protruding from the headstock? I've had suggestions of using 1) plastic tube 2) bearing with sleeve but wonder if these ideas are versatile enough. I guess what I'm asking for is some kind variable diameter i.d. bearing on, perhaps, a vibration absorbing support ...... any suggestions ??? Regards Rob |
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Lathe Suggestions
On Thu, 10 Jul 2003 17:51:15 +0100, Rob Hammond wrote:
What products / ideas exist that will support a long bar (say 10 ft) protruding from the headstock? I've used a bungee cord wrapped around the bar and hooked to a nail in the ceiling. Worked alright at low speeds. -Tom ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Tom Young teyoung at attbi dot com *To reply, remove THIS from address* |
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Lathe Suggestions
Yes, it is very, very important to know how fast the stuff is
turning, exactly what it is made out of and a few other things. We can go into a long enginering discussion about critical speed -- perhaps that is the right thing to do. My point was to bring up the idea, not solve the whole problem -- not enough data was provided. I cannot be more specific without more data. You and I probably agree that the number one issue is a critical speed analysis. Based on a GUESS of the aspect ratio and material, the critical speed is probably very low, like 10 RPM. And yes, people are killed and machinery destroyed by "whipping shafts". "jim rozen" wrote in message ... In article , "frank" says... But the critical speed issue is also a serious problem. If you are getting withing 10% of critical speed you will need to do some real engineering. I envision lots of pillow blocks on a long piece of large box tubing. You need to be more specific about the 'critical speed' problem. What it means is, unless the entire shaft that protrudes is *securely* supported along its ENTIRE length, the machine operator will be confronted with a piece of one inch diamter bar stock that has bent at a 90 degree angle where it emerges from the far side of the headstock, and is WHIPPING around in a huge circle at about 1000 rpm. Anyone and anything in its path becomes so much chopped meat or trash. YOu only need to see this happen once to gain a significant appreciation for the term 'critical.' Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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Lathe Suggestions
Impressive, isn't it? Saw a piece of 3/4" steel pretty much destroy a
coolant system tank and pump and a wooden workbench. Happened real quick, too. (No, I wasn't the one that did it. Just an amazed bystander.) -- Greg "jim rozen" wrote in message ... In article , "frank" says... But the critical speed issue is also a serious problem. If you are getting withing 10% of critical speed you will need to do some real engineering. I envision lots of pillow blocks on a long piece of large box tubing. You need to be more specific about the 'critical speed' problem. What it means is, unless the entire shaft that protrudes is *securely* supported along its ENTIRE length, the machine operator will be confronted with a piece of one inch diamter bar stock that has bent at a 90 degree angle where it emerges from the far side of the headstock, and is WHIPPING around in a huge circle at about 1000 rpm. Anyone and anything in its path becomes so much chopped meat or trash. YOu only need to see this happen once to gain a significant appreciation for the term 'critical.' Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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On 10 Jul 2003 16:32:36 -0700, jim rozen wrote:
You need to be more specific about the 'critical speed' problem. What it means is, unless the entire shaft that protrudes is *securely* supported along its ENTIRE length, the machine operator will be confronted with a piece of one inch diamter bar stock that has bent at a 90 degree angle where it emerges from the far side of the headstock, and is WHIPPING around in a huge circle at about 1000 rpm. Ask me how I know. :-( Gary |
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Ahhhhhhhhh yes, I know exactly what your talking about there. I'll
tell you how I know. Was at work one day, and its supposedly against company policy to do home projects, but we all know how that goes. Decent folks get projects done on the sly others do not. Anyway a fellow came to me and asked if I could machine a shoulder and reduce the round brass stock he had and cut some threads on the end of it. He wanted to make a brass shotgun cleaning rod out of some 5/16" diam brass stock he scrounged. I said sure. I chucked it up in the lathe (about 3 1/2 - 4 feet total length. He was going to get an exact length later and cut it to size. I machined the shoulder, and the lathe was still turning the stock at a "resonable" speed. Someone came in the shop and he got nervous, turned around and bumped into the speed change lever. Lathe ran up in speed, and this brass rod bent in a 90 deg angle and proceeded to catch him in the elbow. It was awfull. It fractured his elbow big time. Not wanting to get me in trouble for his project, he faked a fall out the doorway, at the back of the hanger where the quarry tile at the threshold was always chipping off and had been reported numerous times to the safety office as a trip and stumble hazzard. This action finally got civil engineers to fix the doorway thresholds tile, but his elbow has never been the same since. I have tried numerous times to slip the lathe into a higher rnge but all it did was grind gears, he however managed to do it just by accident. Taught me a lesson, don;t leave anything any longer exctending out of the lathes headstock than necessary, and don't allow anyone around you when your using the machines......**** happens. My pet peave is when someone just walks in and gets nect to you to watch you make chips, or those that proceed to use the chip pan as a foot rest while they shoot the breeze...... On Sun, 13 Jul 2003 15:19:31 GMT, (Gary Coffman) wrote: x-On 10 Jul 2003 16:32:36 -0700, jim rozen wrote: x-You need to be more specific about the 'critical speed' x-problem. x- x-What it means is, unless the entire shaft that protrudes x-is *securely* supported along its ENTIRE length, the x-machine operator will be confronted with a piece of x-one inch diamter bar stock that has bent at a 90 x-degree angle where it emerges from the far side x-of the headstock, and is WHIPPING around in x-a huge circle at about 1000 rpm. x- x-Ask me how I know. :-( x- x-Gary -- Visit my website: http://www.frugalmachinist.com Contents: foundry and general metal working and lots of related projects. Regards Roy aka Chipmaker // Foxeye Opinions are strictly those of my wife....I have had no input whatsoever. Remove capital A from chipmAkr for correct email address |
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In article ,
Gary Coffman wrote: On 10 Jul 2003 16:32:36 -0700, jim rozen wrote: You need to be more specific about the 'critical speed' problem. What it means is, unless the entire shaft that protrudes is *securely* supported along its ENTIRE length, the machine operator will be confronted with a piece of one inch diamter bar stock that has bent at a 90 degree angle where it emerges from the far side of the headstock, and is WHIPPING around in a huge circle at about 1000 rpm. Ask me how I know. :-( In my experience, I've not had any problems by using some PVC pipe not too much larger than the stock in a cradle to constrain the outboard end (and actually the full length outside the spindle. I've got a 1-1/2" ID PVC pipe for 3/4" and 1" stock, and another pipe of the same size with a pair of caps bored to be a nice fit on some smaller PVC pipe for the thinner stuff -- 1/4", 3/16" etc). The pipe is secured to the cradle by a Bungee cord over the pipe. This is enough to keep the end from starting to bend out past some critical diameter. Once it does that, there is no stopping it, of course. I also don't run very fast -- typically 650 RPM for the six foot long 3/4" brass rod, and perhaps a maximum of 1200 RPM for the really skinny stuff. For the 3/4" bar, I also have a Plexiglass bushing which fits in the end of the collet drawbar to keep the bar concentric at that point. I've now finally gotten compressed air, so I may make up some pistons for the pipes to use as stock feed devices, so I don't have to stop the spindle to feed stock. Just add a foot switch -- and keep the PVC leaky enough so it won't develop full pressure, perhaps with an intentional leak at the end of stroke. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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In article ,
Gunner wrote: On 13 Jul 2003 14:01:07 -0400, (DoN. Nichols) wrote: I've now finally gotten compressed air, so I may make up some pistons for the pipes to use as stock feed devices, so I don't have to stop the spindle to feed stock. Just add a foot switch -- and keep the PVC leaky enough so it won't develop full pressure, perhaps with an intentional leak at the end of stroke. Enjoy, DoN. If you are running a turret, its very very easy to make a parts Puller, rather than a pusher and you can simply make up a number of pullers for various sized stock. The advantage of a puller over a pnuematic or hydraulic pusher really comes into play with small diameter stock. I thought that the pullers were better in an ASM or perhaps a CNC with turret -- with some way to activate them automatically. I don't see a way of activating one on my turret. (And aside from that, I'm already using all six stations on the turret, with the feed stop running double duty as a center drill.) 1) Stop/center drill 2) Knurl OD 3) Box tool to reduce a portion of the OD 4) Geometric die head to thread un-knurled portion of the OD 5) Drill for tap 6) Tap (then to the carriage for grooving at the base of the thread and parting off while I break the edges with a file.) Next setup I'll be using one of the multi-tool Aloris holders so I can do the parting of the current one and the grooving of the next in a single pass. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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In article , Gunner says...
I went into a shop a few years ago, where this had been done with a piece of 1. 25" leadloy. The machinist had put the 5' stubb on stands but didnt secure the stands very well. It actually moved that 16" lathe about 4 feet before they managed to get the main power turned off. Screwed up the floor, the walls, several workbenches and the machinists chance to advance in that company...... Apparently it also happened at New Hampshire Ball Bearing as well. With the same results, the guy was instantly fired. But this was a piece of two inch steel they make bearing races out of. Trashed a brand new OKUMA lathe. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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On 13 Jul 2003 19:49:26 -0700, jim rozen
wrote: In article , says... I thought that the pullers were better in an ASM or perhaps a CNC with turret -- with some way to activate them automatically. I don't see a way of activating one on my turret. (And aside from that, I'm already using all six stations on the turret, with the feed stop running double duty as a center drill.) 1) Stop/center drill Whoa stop right there Don! You have just jogged my memory from when I was setting up my turrret lathe. I've only done a few parts on it so far, some were brass thumbscrews for an antique radio, and some were some aluminum thumbscrews for an electric timer. But.... The real question is, *how* do you get the stock stop (in this case, the point of your centerdrill) to hold an accurate length when you snap the collet closed??! The most I can figure out is, one either a) tries to get the variation in length of stock protuding from the collet once it is closed, to be about the same each time, ie. try to keep the error small and constant, but accept it as an overall finished part tolerance, or b) get it close with the stop, and then use a crosslide station, or a facing tool in the turret, to set an absolute length that does not depend on the stock's protrusion from the collet at the beginning of the cycle. I think I was seeing variation on the order of between five and ten thou in length, when I was using the stock stop in the turret station alone. Does this sound about right or is there a secret skill that turret lathe operators know to keep this smaller? Thanks - Jim Lots of guys make the cut off as the FIRST operation, followed by bar advance. One has to make the first part scrap to determine just what the drawback of the collet will be, then all other operations are set to that length. The second operation is generally a facing, which brings it to proper length if the bar is a bit under or over sized, then all other operations are done in order, followed by cutting off, which is the start of the next cycle. This works really well if you are not using dead length collets. Gunner "What do you call someone in possesion of all the facts? Paranoid.-William Burroughs |
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On 14 Jul 2003 07:05:38 -0700, jim rozen
wrote: In article , Gunner says... One has to make the first part scrap to determine just what the drawback of the collet will be, then all other operations are set to that length. OK, so at this point the best tolerance I could do would be +/- 0.005 or so on the O/A length. The second operation is generally a facing, which brings it to proper length if the bar is a bit under or over sized, then all other operations are done in order, followed by cutting off, which is the start of the next cycle. This works really well if you are not using dead length collets. That obviously gets it a lot closer - but it takes another tool location for the facing off. Either on the cross slide or on the turret. Jim Correct. Lots of guys use the crosslide front position for this facing op, With the cut off in the back position, cut off tool upside down for chip control. Add a tool, but get dead nuts accuracy. Gunner "What do you call someone in possesion of all the facts? Paranoid.-William Burroughs |
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In article ,
jim rozen wrote: In article , says... [ ... ] 1) Stop/center drill Whoa stop right there Don! You have just jogged my memory from when I was setting up my turrret lathe. I've only done a few parts on it so far, some were brass thumbscrews for an antique radio, and some were some aluminum thumbscrews for an electric timer. But.... The real question is, *how* do you get the stock stop (in this case, the point of your centerdrill) to hold an accurate length when you snap the collet closed??! First off -- the centerdrill point retracts to below the face of the stop, so it doesn't ding the end of the work while setting length. There was one of these shown in Moultrecht's two-volume _Machine Shop Practice_, so I just made one of my own. Not as nice for stock stop as the ones with a bearing-mounted rotating pad on the end, but it saves me a station. :-) Now -- what I do is to pull the rod stock too far by about a half inch, then apply the lever to the point where there is some drag, and use the turret with the stock stop to push it back (with most of the slack taken out by the lever. If the stock is dragging on the collet, there isn't much travel left in the collet before it locks up. Balance by feel the drag as you approach the end of travel on the turret, and then lock up. There will be some stock movement as you lock up, but it is pretty minimal, and pretty consistent. The most I can figure out is, one either a) tries to get the variation in length of stock protuding from the collet once it is closed, to be about the same each time, ie. try to keep the error small and constant, but accept it as an overall finished part tolerance, or This is essentially what I do -- with the drag technique minimizing the variation. b) get it close with the stop, and then use a crosslide station, or a facing tool in the turret, to set an absolute length that does not depend on the stock's protrusion from the collet at the beginning of the cycle. I tried this, and decided that it wasted too much time when doing a run of parts. As well as wasting a little bit more stock. I think I was seeing variation on the order of between five and ten thou in length, when I was using the stock stop in the turret station alone. Does this sound about right or is there a secret skill that turret lathe operators know to keep this smaller? Well ... I don't know about *secret*. I developed this out of need, and didn't learn it from anyone else, but I suspect that it has been similarly discovered by many others. Of course, there are styles of collets which have zero stock motion when being closed, but I understand that they are a bit less consistent in concentricity, and the 5C with lever is what I have, so I just learned to work with it. :-) Thanks - Jim You're welcome. Now to see what others answered to your question. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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In article ,
Gunner wrote: On 13 Jul 2003 21:31:17 -0400, (DoN. Nichols) wrote: In article , Gunner wrote: On 13 Jul 2003 14:01:07 -0400, (DoN. Nichols) wrote: I've now finally gotten compressed air, so I may make up some pistons for the pipes to use as stock feed devices, so I don't have to [ ... ] If you are running a turret, its very very easy to make a parts Puller, rather than a pusher and you can simply make up a number of [ ... ] don't see a way of activating one on my turret. (And aside from that, I'm already using all six stations on the turret, with the feed stop running double duty as a center drill.) 1) Stop/center drill [ ... ] In lue of the parts stop, make a puller. Simply bore a chunk of Crs or other common metal to .005 smaller than your work, and turn the other end to fit your turret. Then slit the bored end lengthwise. Sounds easy enough to make -- but that leaves me one station short, unless there is a way to combine a center drill with the puller. The swarf from the center drilling might interfere with the puller's operation. Perhaps mill out the rim on the bottom, so it pours out? Extend your work, close the collet. Extend the puller and it will slip over the end of your work piece. Release the collet, and retract the puller to the proper distance. Close the collet, retract the puller a smidge more, pulling it off the workpiece. The first pull is marked or set as your dead stop. Proceed with the rest of your operations. The stub should be long enough now to slide the puller over it, retract, and proceed. The puller is only a friction fit over the end of your bar. Hmm ... the turret that I have has only one stop per station, so getting it *past* the stop to pick up the workpiece and then to a preset position for the actual collet clamping might be a problem. Worth considering if I have a setup which uses fewer stations, so the puller first station, stock stop second, and that leaves four stations which should be enough for some of my multi-part projects. Just this one project which uses all stations plus one. :-) Countless machine shops use a puller every day, even on CNC, particularly for short bars. There it would be particularly nice, as I have to keep a chunk of stock on hand to act as a pusher once the bar is inside the spindle -- or grip it with pliers and pull. :-) The second type of "bar feeder" is one that is gravity fed, and is very easy to make in a home shop. Simply slot a piece of galvanized pipe lengthwise, and make up a slider that fits inside, with a stub protruding through through the slot. Attach a cord to the stub, and at the end closest to the lathe, on the front support, attach a rotating drum, and wrap the cord around the drum, and hang a weight from it. As you slide in the bar, it winds up the weight. Gravity wants to pull the weight down, putting feed pressure on the bar stock. Virtually all of the Traub, Tornos, etc etc Swiss style screw machines use this simple and effecient type of bar feeder. Nice! And its a snap to make any length you have room for. Ah -- the "have room for" question. :-) Six foot bar stock (as I get from MSC) I can handle nicely. Beyond that, I see problems. :-) Thanks, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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