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drill bit size for cutting threads ?
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RCT
Posted 10/16/2012 20:49 (#2644080)
Subject: drill bit size for cutting threads ?



S.C. Minn

Looking for a chart that would show me what size hole to drill for each size of tap I would use to tap threads.
TIA 

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Matt NCOK
Posted 10/16/2012 20:57 (#2644108 - in reply to #2644080)
Subject: RE: drill bit size for cutting threads ?



http://kwikwing.redirectme.net/R&K-Shop/Decimal&TapSizes/StarrettDe...
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exit
Posted 10/16/2012 20:59 (#2644112 - in reply to #2644080)
Subject: Re: drill bit size for cutting threads ?


Athens, Ga
http://www.engineershandbook.com/Tables/taphole.htm
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SD-455
Posted 10/16/2012 21:37 (#2644196 - in reply to #2644080)
Subject: RE: drill bit size for cutting threads ?


Northeast Indiana (Auburn)		Rule of thumb divide the number of threads per inch into 1 then subtract this number from the thread size. example 3/8-16 thread, divide 1 by 16= .0625, subtract .0625 from .375(3/8")= .3125(5/16" drill size. 1/2-13 thread =.500-.077=.423 drill. 1/4-20 thread is .250-.050= .200 drill. Metric size 24mm X 1.5 pitch take the pitch from the size 24-1.5=22.5mm drill.

Edited by SD-455 10/16/2012 21:38
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PaKettle
Posted 10/16/2012 21:38 (#2644206 - in reply to #2644080)
Subject: RE: drill bit size for cutting threads ?



Lenawee Co Michigan		Most drill indexes have that info stamped on the front drill rack.
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Gerald J.
Posted 10/17/2012 04:34 (#2644842 - in reply to #2644080)
Subject: Re: drill bit size for cutting threads ?



Most tables are for 50% thread depth which ignores extrusion of the thread and can lock up the tap which usually breaks the tap in the hole. I prefer 75% which will be strong enough to strip the bolt before the threads in the hole. I did a paper on it displaying charts a couple years ago. Its at http://www.geraldj.networkiowa.com/papers/CSVHF2010/tappingupdate.p...

Gerald J.
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