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How to callout how to drill threaded holes
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Posted by: Hitokiri03

01/06/2011, 14:03:28

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I am making an engineering drawing for a plate that has some holes drilled for a couple different kinds of screws and I don't know how to do a callout for how to drill the hole and co'bore it. The two sizes are 3/8-16 coarse thread and 1/4-28 fine thread. Thanks for the help.







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: How to callout how to drill threaded holes
: How to callout how to drill threaded holes -- Hitokiri03
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Posted by: Kelly Bramble

01/12/2011, 17:38:39

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Well, generally we don't specify the pre-drill hole for tapping. We call out the threaded hole feature end-item requirement e.g.

Arrow pointing to threaded hole feature with 3/8 - 16 UNC -2B

or

5X .250-28 UNF - 2A, .500 MIN FULL THREAD

5X = means there are five holes that must meet this requiremnt.








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: : How to callout how to drill threaded holes
: : How to callout how to drill threaded holes -- Kelly Bramble
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Posted by: tk369

01/19/2011, 09:38:28

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According to my Holo-Krome screw selector guide, a 1/4-28 UNF-2A tap drill is dia .2187. A 3/8-16 UNC-2B tap drill is dia .313.

A typical callout would be:

3/8-16 UNC 2B
TAP DRILL DIA .313

or

1/4-28 UNF-2A
TAP DRILL DIA .2187








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