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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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tap formula
My son spent another week in Tebis training last week...
http://en.wikipedia.org/wiki/Tebis So, I asked him what he learned. He's now so far into tooling design I can hardly follow it. he's now lead CAM programmer for his company. But he did tell me this little fact. For a tap drill size you subract the recipricle of the lead from the nominal size. ie. for a 3/8 x 16 thread subrtract 1/16 from 3/8 and use tap drill size 5/16. For metric taps subtract the lead. ie. for M10 x 2.0, 10 -2 = 8 mm tap drill size. I had always just looked at my handy tap chart. |
#2
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tap formula
On Fri, 06 Sep 2013 15:23:33 -0500, Karl Townsend
wrote: My son spent another week in Tebis training last week... http://en.wikipedia.org/wiki/Tebis So, I asked him what he learned. He's now so far into tooling design I can hardly follow it. he's now lead CAM programmer for his company. But he did tell me this little fact. For a tap drill size you subract the recipricle of the lead from the nominal size. ie. for a 3/8 x 16 thread subrtract 1/16 from 3/8 and use tap drill size 5/16. For metric taps subtract the lead. ie. for M10 x 2.0, 10 -2 = 8 mm tap drill size. I had always just looked at my handy tap chart. Cool tip! Saved and remembered (hopefully.) Thanks, Karl. -- It is common sense to take a method and try it. If it fails, admit it frankly and try another. But above all, try something. -- Franklin D. Roosevelt |
#3
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tap formula
On 9/6/2013 8:10 PM, Larry Jaques wrote:
On Fri, 06 Sep 2013 15:23:33 -0500, Karl Townsend wrote: My son spent another week in Tebis training last week... http://en.wikipedia.org/wiki/Tebis So, I asked him what he learned. He's now so far into tooling design I can hardly follow it. he's now lead CAM programmer for his company. But he did tell me this little fact. For a tap drill size you subract the recipricle of the lead from the nominal size. ie. for a 3/8 x 16 thread subrtract 1/16 from 3/8 and use tap drill size 5/16. For metric taps subtract the lead. ie. for M10 x 2.0, 10 -2 = 8 mm tap drill size. I had always just looked at my handy tap chart. Cool tip! Saved and remembered (hopefully.) Thanks, Karl. -- It is common sense to take a method and try it. If it fails, admit it frankly and try another. But above all, try something. -- Franklin D. Roosevelt that cool tip follows from 6 degree thread pitch - 1/2 base times height - it's in all the handbooks. |
#4
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tap formula
On 9/7/2013 1:20 PM, . wrote:
that cool tip follows from 6 degree thread pitch - 1/2 base times height ... You mean 60 degree, of course. And "... 1/2 base times height" is the area of a triangular thread cross section & has nothing to do with diameters. The height of the triangle is P/2 * SQRT(3)(where P = pitch), which is the difference between the major & minor _radii_ of a _triangular_ form thread. The difference in diameters is then P*SQRT(3) which is quite a bit larger than P (1.7 times). But the standard thread form is not a triangle - the crest and root are both truncated. So by a happy cancellation of inaccuracies (the pitch being to small a difference for triangular threads and the standard thread not being triangular), the pitch is a close-enough difference between major & minor diameters. I suppose that if one went through the geometry of the truncations, the difference would come out being (almost)equal to the pitch. But it certainly does not come from the height of a 60 degree triangle whose base is equal to the pitch. Bob |
#5
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tap formula
"Bob Engelhardt" wrote in message ... On 9/7/2013 1:20 PM, . wrote: that cool tip follows from 6 degree thread pitch - 1/2 base times height ... You mean 60 degree, of course. And "... 1/2 base times height" is the area of a triangular thread cross section & has nothing to do with diameters. The height of the triangle is P/2 * SQRT(3)(where P = pitch), which is the difference between the major & minor _radii_ of a _triangular_ form thread. The difference in diameters is then P*SQRT(3) which is quite a bit larger than P (1.7 times). But the standard thread form is not a triangle - the crest and root are both truncated. So by a happy cancellation of inaccuracies (the pitch being to small a difference for triangular threads and the standard thread not being triangular), the pitch is a close-enough difference between major & minor diameters. I suppose that if one went through the geometry of the truncations, the difference would come out being (almost)equal to the pitch. But it certainly does not come from the height of a 60 degree triangle whose base is equal to the pitch. Quicker to simply look at a chart than to convert say 1/13" or 1/11" into a decimal format... I've had most of the common tap drill sizes memorized nearly forever anyways although frequently I'll use a slightly larger size, depending on the actual job |
#6
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tap formula
"PrecisionmachinisT" wrote in message news:cq2dnU9ZJ5D_ibHPnZ2dnUVZ_vGdnZ2d@scnresearch. com... I've had most of the common tap drill sizes memorized nearly forever anyways although frequently I'll use a slightly larger size, depending on the actual job Same here, a larger hole makes hand tapping so much easier and cuts down on tap breakage. A common internal thread, drilled so that it results in 50% of full thread will break the external thread, before the internal thread will strip. A common internal thread drilled out so that it contains 100% of full thread is only 5% stronger than a 75% height of thread, yet it requires 3 times the power to tap. http://www.kennametal.com/kennametal...rill-size.html Best Regards Tom. |
#7
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tap formula
On 9/6/2013 11:10 PM, Larry Jaques wrote:
On Fri, 06 Sep 2013 15:23:33 -0500, Karl Townsend wrote: My son spent another week in Tebis training last week... http://en.wikipedia.org/wiki/Tebis So, I asked him what he learned. He's now so far into tooling design I can hardly follow it. he's now lead CAM programmer for his company. But he did tell me this little fact. For a tap drill size you subract the recipricle of the lead from the nominal size. ie. for a 3/8 x 16 thread subrtract 1/16 from 3/8 and use tap drill size 5/16. For metric taps subtract the lead. ie. for M10 x 2.0, 10 -2 = 8 mm tap drill size. I had always just looked at my handy tap chart. Cool tip! Saved and remembered (hopefully.) Thanks, Karl. -- It is common sense to take a method and try it. If it fails, admit it frankly and try another. But above all, try something. -- Franklin D. Roosevelt Do you have "CRS" disease? (can't remember ****) Welcome to the ---whatever it is! |
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