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True Position Tolerance VS Callout Tolerance
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Posted by: brice arnold

12/09/2005, 17:33:27

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I have a drawing with a hole position callout of .001". I spoke with a machine shop about the production of this part and they informed me the the true position tolerance for a .001" callout is actually .0003565". Upon asking about this he could not go into detail but informed be that it is a fairly common factor (.3565) which is applied to positioning tolerance and involves a series of calculations.

Is there anyone familiar with this factor, that could offer a better explination? Also, does anyone know of a source for these calculations? I have some simple GD&T booklets which make no mention of this factor.






Modified by brice arnold at Fri, Dec 09, 2005, 17:34:57

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Re: True Position Tolerance VS Callout Tolerance
Re: True Position Tolerance VS Callout Tolerance -- brice arnold Post Reply Top of thread Forum
Posted by: traingdt

12/10/2005, 10:37:23

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The factor that the machine shop told you about is probably meant to convert diametrical tolerances to x-y tolerances, since that is what machines "think" in. But two points: first, I think the factor would be .0003535. This is calculated by assuming that the .001 position tolerance was a diameter; then cut that in half so the tolerance is now .0005 in any radial direction. Then use the Pythagorean Theorem to break that into vertical and horizontal components: .0005 = sqrt(x^2 + y^2).
But the second point: realize that by doing this, they are cheating themselves out of a small portion of the tolerance zone. (Sketch a circular area and then a triangle from the center to the edge.) They are bounding themselves within a square zone that is inscribed within the full circle. But I suppose that's the tradeoff in converting back to x-y coordinates.






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Re: True Position Tolerance VS Callout Tolerance
Re: True Position Tolerance VS Callout Tolerance -- brice arnold Post Reply Top of thread Forum
Posted by: randykimball

12/09/2005, 19:19:52

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Try this...

http://www.engineersedge.com/calculators.htm




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