Determining drill bit size for a tap?

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06-30-2003, 11:00 PM

jmd

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Determining drill bit size for a tap?

I am using a 13/16-16 tap. What size drill bit do I need? Charts I've found so far online jump from 3/4 to 7/8.

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06-30-2003, 11:12 PM

jmd

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Re: Determining drill bit size for a tap?

okay for 3/4-16 thread, it's an 11/16" bit
for 7/8-14 thread, it's a 13/16" bit.

any reason I woulddn't be safe w/ a 3/4" bit?

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06-30-2003, 11:42 PM

2xLS1

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Re: Determining drill bit size for a tap?

Use some dial calipers to measure the inside threads of the tap.

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07-01-2003, 08:09 AM

ScottyG

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Re: Determining drill bit size for a tap?

jmd:
A 20mm thread uses a 47/64" drill. Since 13/16 is slightly larger than 20mm, and 3/4" is slightly larger than 47/64" this further supports the use of a 3/4" drill.

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07-01-2003, 10:17 AM

jmd

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Re: Determining drill bit size for a tap?

Don on the Monte Carlo mailing list posted this nice link on bit sizes:

http://www.haascnc.com/Training/Hype...imal_Chart.pdf

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07-01-2003, 10:32 AM

Cal

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Re: Determining drill bit size for a tap?

You may want to go slightly bigger than what the charts say in some cases depending on the material you're trying to tap. If it is something gummy like stainless steel, for example.

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