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Tolerance standard for drilled holes Don
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Posted by: tcyr

01/25/2010, 17:51:57

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Thanks for posting your chart for the standard tolerance for drilled holes. My company has the same chart in our Engineering Practices Manual. Problem is, no one uses it beyond the design stage. There is no note or specification or standard called out on drawings so drilled holes are treated like any other feature by QA and Production.

This causes a lot of inefficiencies. For example, to draw a clearance hole for a fastener, there either has to be a tolerance specified for that hole or an interference condition could exist if the tolerance in the drawing tolerance block is used to define minimum hole size.

Is ignoring drilled hole tolerances common for other companies? Or has something been lost somewhere in the history of design and manufacturing so that the engineering community is truly ignorant of it? I don't see any specification that I can refer to that might lend credence to the existence of an accepted standard.








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: Tolerance standard for drilled holes
: Tolerance standard for drilled holes -- tcyr Post Reply Top of thread Engineering Forum
Posted by: Tunalover

02/10/2010, 13:44:01

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There has to be some variance called out on the field of the drawing. No machinist is going to look up a standard size tolerance in a spec called out in the title block. My company doesn't use standard drill sizes let alone standard drill size tolerances but I do. I use the Air Force-Navy Aeronautical Design Standard AND10387 which lists standard drills by size and provides size tolerances. If you can't find the standard I can fax you a copy (it's one page) if you reply with your fax number and name.







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: Tolerance standard for drilled holes
: Tolerance standard for drilled holes -- tcyr Post Reply Top of thread Engineering Forum
Posted by: Kelly Bramble

01/25/2010, 19:10:43

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Actually there are several ANSI specs. that suggest industry standard tolerances.

These industry standard tolerances are based on a variety of criteria - such as function (application) or manufacturing process capability. In general, tolerances are based on function first then the design is optimized for manufacturability.

Engineers Edge has several pretty good and proven standard tolerance charts here:

/tolerance_chart.htm








Modified by Kelly Bramble at Mon, Jan 25, 2010, 19:11:38


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Posted by: jboggs

01/26/2010, 07:37:22

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I assume QA is referring to some standard tolerance guide on the drawing title block somewhere. See if you can get a reference to the drilled hole standard added to that part of the title block, or to some standard note. That makes it part of the drawing. It is in the best interests of both Engineering and QA to have some well defined (if not written) agreement on how drilled holes will be interpreted.







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