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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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#1
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Turning an O-ring groove in piston
So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? |
#2
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Turning an O-ring groove in piston
"Bob La Londe" wrote in message ... So what's the spproscribedsp prescribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? LOL. Silicone o-ring for modest heat. Upto about 325 degrees. |
#3
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Turning an O-ring groove in piston
Bob La Londe wrote: "Bob La Londe" wrote in message ... So what's the spproscribedsp prescribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? LOL. Silicone o-ring for modest heat. Upto about 325 degrees. Most O-rings I look at are seated in square grooves. I believe you need the extra space afforded by the square groove to allow the O-ring to deform and seal properly. For a piston though, you should probably be looking at cup seals and the like on McMaster.com. |
#4
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Turning an O-ring groove in piston
In article ,
"Bob La Londe" wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? Most o-ring grooves are square - there's little or no need to match the profile of the ring, just get the size right so the ring compresses adequately to work... If you want a round bottom, and you are HSMing rather than production, just use a round-nosed tool and take it easy, unless you've gone and decided to work in stainless where you can't take an easy cut, in which case you'll need a machine that will stand a real cut. Roughing out with a V does not reduce the power needed to make the final cut at full radius, and making the cut in any normal material is not likely to dull the tool much. -- Cats, coffee, chocolate...vices to live by |
#5
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Turning an O-ring groove in piston
On May 7, 9:29*am, "Bob La Londe" wrote:
So what's the proscribed method? *I expect I need a pretty consistent radius bottom. *What's the best way. *Make a rough semi V lathe bit, and then make a decent round one to finish? The Parker O-Ring Handbook (9 Mb) discusses some of the design criteria for o-ring grooves. See Section 4: http://www.parker.com/literature/ORD...g_Handbook.pdf |
#6
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Turning an O-ring groove in piston
"Pete C." wrote in message
ster.com... Bob La Londe wrote: "Bob La Londe" wrote in message ... So what's the spproscribedsp prescribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? LOL. Silicone o-ring for modest heat. Upto about 325 degrees. Most O-rings I look at are seated in square grooves. I believe you need the extra space afforded by the square groove to allow the O-ring to deform and seal properly. For a piston though, you should probably be looking at cup seals and the like on McMaster.com. Not an engine piston. A modest temp single stroke hand injection pump piston. After I posted I was thinking a square groove might work better. Thanks. I have not grooved the piston itself yet. |
#7
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Turning an O-ring groove in piston
On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? Check this out:- http://www.parker.com/literature/ORD...g_Handbook.pdf Pretty much all you need to know about static and dynamic O-ring seals. "The shape of the seal groove is unimportant as long as it results in proper compression of the seal between the bottom of the groove and the cylinder wall, and provides room for the compressed material to flow so that the seal is not solidly confined between metal surfaces" |
#8
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Turning an O-ring groove in piston
Bob La Londe wrote: "Pete C." wrote in message ster.com... Bob La Londe wrote: "Bob La Londe" wrote in message ... So what's the spproscribedsp prescribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? LOL. Silicone o-ring for modest heat. Upto about 325 degrees. Most O-rings I look at are seated in square grooves. I believe you need the extra space afforded by the square groove to allow the O-ring to deform and seal properly. For a piston though, you should probably be looking at cup seals and the like on McMaster.com. Not an engine piston. A modest temp single stroke hand injection pump piston. After I posted I was thinking a square groove might work better. Thanks. I have not grooved the piston itself yet. Not engine piston, they use very different seals, think hydraulic piston as most of those use some variety of cup seal. |
#9
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Turning an O-ring groove in piston
On May 7, 11:04*am, "Denis G." wrote:
On May 7, 9:29*am, "Bob La Londe" wrote: So what's the proscribed method? *I expect I need a pretty consistent radius bottom. *What's the best way. *Make a rough semi V lathe bit, and then make a decent round one to finish? The Parker O-Ring Handbook (9 Mb) discusses some of the design criteria for o-ring grooves. *See Section 4:http://www.parker.com/literature/ORD...g_Handbook.pdf The other big name in o-rings is Apple. I am sure they also have information on the web about grooves for O-rings. Dan |
#10
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Turning an O-ring groove in piston
Pete C. wrote:
Bob La Londe wrote: "Bob La Londe" wrote in message ... So what's the spproscribedsp prescribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? LOL. Silicone o-ring for modest heat. Upto about 325 degrees. Most O-rings I look at are seated in square grooves. I believe you need the extra space afforded by the square groove to allow the O-ring to deform and seal properly. For a piston though, you should probably be looking at cup seals and the like on McMaster.com. Correct. Most O-rings are intended to be seated in nearly square (rectangular) grooves. Rubber is essentially like a fluid ... it is nearly incompressable. When pressure is applied it DEFORMS, but does not compress significantly. That's why it's used for some kinds of one-sided-mold stamping operations. It applies a uniform pressure just like a hydraulic fluid. Assuming a square groove with a round O-ring, the groove should be about the same width as the O-ring's diameter, and bit less in depth than the ring's diameter. Then, when the cover-plate (or whatever) moves to put pressure on the O-ring, it deforms, swelling sidewise to press against the sides of the groove as well as the bottom. It effectively makes a three-point seal in the groove, with one seal against the closing element. A round-bottom groove doesn't allow the ring to deform properly, and it will "mushroom" out of the groove, deforming oddly, since there's no other place for it to deform into. Now, it's true that a round bottom groove CAN work, for low-pressure or unusal applications, where the O-ring is not overly deformed, but it's not what's usually recommended. Check most any o-ring manufacturer for specs. Dan Mitchell ============ |
#11
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Turning an O-ring groove in piston
"Spehro Pefhany" wrote in message ... On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe" wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? Check this out:- http://www.parker.com/literature/ORD...g_Handbook.pdf Pretty much all you need to know about static and dynamic O-ring seals. "The shape of the seal groove is unimportant as long as it results in proper compression of the seal between the bottom of the groove and the cylinder wall, and provides room for the compressed material to flow so that the seal is not solidly confined between metal surfaces" That paragraph pretty much sums it up and describes one of my problems on my first tests. I guess I need to go make some square lathe tips in the right sizes. I was going for an exact fit round groove. |
#12
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Turning an O-ring groove in piston
"Pete C." wrote in message
ster.com... Bob La Londe wrote: "Pete C." wrote in message ster.com... Bob La Londe wrote: "Bob La Londe" wrote in message ... So what's the spproscribedsp prescribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? LOL. Silicone o-ring for modest heat. Upto about 325 degrees. Most O-rings I look at are seated in square grooves. I believe you need the extra space afforded by the square groove to allow the O-ring to deform and seal properly. For a piston though, you should probably be looking at cup seals and the like on McMaster.com. Not an engine piston. A modest temp single stroke hand injection pump piston. After I posted I was thinking a square groove might work better. Thanks. I have not grooved the piston itself yet. Not engine piston, they use very different seals, think hydraulic piston as most of those use some variety of cup seal. Ok... if I ever go to high production (if I do remind me I'm a hack) I'll look at that. Most of the "commercial" models of this are using an o-ring. |
#13
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Turning an O-ring groove in piston
On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? Use a rectangular groove. Lots of information (11 meg download) in "The Sealman's O-Ring Design Handbook" http://www.physics.harvard.edu/servi...g_handbook.pdf |
#14
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Turning an O-ring groove in piston
On May 7, 10:39*am, " wrote:
On May 7, 11:04*am, "Denis G." wrote: On May 7, 9:29*am, "Bob La Londe" wrote: So what's the proscribed method? *I expect I need a pretty consistent radius bottom. *What's the best way. *Make a rough semi V lathe bit, and then make a decent round one to finish? The Parker O-Ring Handbook (9 Mb) discusses some of the design criteria for o-ring grooves. *See Section 4:http://www.parker.com/literature/ORD...g_Handbook.pdf The other big name in o-rings is Apple. *I am sure they also have information on the web about grooves for O-rings. Dan Thanks, I found them and bookmarked them for future reference (though you have to register to read their technical library). |
#15
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Turning an O-ring groove in piston
Don Foreman wrote:
On Fri, 7 May 2010 07:29:29 -0700, "Bob La wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? Use a rectangular groove. Lots of information (11 meg download) in "The Sealman's O-Ring Design Handbook" http://www.physics.harvard.edu/servi...g_handbook.pdf What everybody said. I've had good luck with a cutoff tool ground to the proper width and the corners lightly stoned. If you want the seal to hold a high vacuum, the bottom of the groove will probably have to be polished. In general I prefer to design with metric O-rings as there's a much wider range of sizes. |
#16
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Turning an O-ring groove in piston
On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? No..use the round one to start and finish with. If you have a tool and cutter grinder and can make some fixtures..you can turn out a decent half round tool On the other hand...unless you are handling really high pressures...you CAN often times get away with a simple V groove. Gunner -- "First Law of Leftist Debate The more you present a leftist with factual evidence that is counter to his preconceived world view and the more difficult it becomes for him to refute it without losing face the chance of him calling you a racist, bigot, homophobe approaches infinity. This is despite the thread you are in having not mentioned race or sexual preference in any way that is relevant to the subject." Grey Ghost |
#17
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Turning an O-ring groove in piston
"Bob La Londe" wrote in message ... "Bob La Londe" wrote in message ... So what's the spproscribedsp Ah, you caught yourself ! Proscribe means to ban, veto, bar, forbid, exclude, make illegal, disallow, rule out etc. Prescribe would be a better choice. In any case, thanks to your question, I'm about to learn something. Ivan Vegvary |
#18
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Turning an O-ring groove in piston
"Bob La Londe" wrote in message ... So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? It has been a few years, but like others have said, just go with a square groove. Seems to me we would make the groove same width as the o-ring, and the depth 90% of the thickness, .250 thick ring, cut the groove .225 deep. Now that depends on your clearance from the piston and cylinder wall too, so I suppose you should go with the cylinder diameter, minus 2x of 90% of the o-ring thickness. so .250x90%x2 subtracted from the cylinder diameter. |
#19
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Turning an O-ring groove in piston
On 5/7/2010 11:04 AM, Denis G. wrote:
On May 7, 9:29 am, "Bob La wrote: So what's the proscribed method? I expect I need a pretty consistent radius bottom. What's the best way. Make a rough semi V lathe bit, and then make a decent round one to finish? The Parker O-Ring Handbook (9 Mb) discusses some of the design criteria for o-ring grooves. See Section 4: http://www.parker.com/literature/ORD...g_Handbook.pdf http://www.allorings.com/ I like this site. Click on "O-Ring Gland Design" Randy |
#20
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Turning an O-ring groove in piston
What's that Lassie? You say that Greg O fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue by Fri, 7 May 2010 18:03:41 -0500: It has been a few years, but like others have said, just go with a square groove. Seems to me we would make the groove same width as the o-ring, and ... No. The width of the groove should be equal or greater than the width of the O-ring. -- Dan H. northshore MA. |
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