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what size drill bit for 1/4 20 tap?

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Old 02-12-2004, 12:01 AM
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themanimal
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Default what size drill bit for 1/4 20 tap?

I am taping holes for my wing bolts, I have the 1/4 20 bolts and tap but can't remember what size drill bit I need to use.

If its 1/4" I'm going to feel stupid.

Thanks.
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Old 02-12-2004, 12:25 AM
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Default RE: what size drill bit for 1/4 20 tap?

Use a number 7 drill bit. If you don't have one, you will have to pick one up at the hardware store.
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Old 02-12-2004, 12:46 AM
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Default RE: what size drill bit for 1/4 20 tap?

Hole tapping requires odd size bits. This numbered bits are sized by wire gauge. Here is a link that shows a Craftsman set. You can buy them individually if the whole set is not needed.
http://www.sears.com/sr/javasr/produ...id=00906819000

Eric
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Old 02-12-2004, 01:19 AM
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Default RE: what size drill bit for 1/4 20 tap?

A #7 drill bit.
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Old 02-12-2004, 01:44 AM
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Lee Belew
 
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Default RE: what size drill bit for 1/4 20 tap?

themanimal

This might be handy to you the next time you need to drill and tap a hole.

Have fun flying

Lee
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Old 02-12-2004, 09:10 AM
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Default RE: what size drill bit for 1/4 20 tap?

a 3/16" bit is close enough if you're tapping wood.
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Old 02-12-2004, 10:34 AM
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Default RE: what size drill bit for 1/4 20 tap?

OR if you are tapping wood, and you are going to go buy a bit, USE A NUMBER 8 INSTEAD OF 7....I have found that going down one size when tapping wood works VERY WELL....A #7 gives you the proper contact percentage for metal.
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Old 02-12-2004, 01:05 PM
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Default RE: what size drill bit for 1/4 20 tap?

Cafeen's right, if it's wood a 3/16 will work. A 13/64 is better yet. (it's only 2 thousanths of an inch larger than a #7 -- That's about the thickness of a human hair) (No, not a RED hair)
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Old 02-12-2004, 04:16 PM
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Default RE: what size drill bit for 1/4 20 tap?

you'd be suprized how small a drill will work if tapping wood. You can get away with a 1/8 inch drill for a 1/4-20 tap in a pinch. Its a bit harder to tap out the hole... you have to back out and clear the chips a lot.

One time, I actually drilled and tapped in one step. It worked but it was very slow.

A good tap and die set will list different pilot drill sizes for different materials to get the best threads. When you are cutting threads in soft metal (brass and similar), part of the metal bulges in toward center, so you don't want quite as large a hole diameter as when doing steel or cast iron.
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Old 02-12-2004, 07:14 PM
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Default RE: what size drill bit for 1/4 20 tap?

Most quality taps have the recommended drill size stamped right on them.
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Old 02-12-2004, 08:43 PM
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Default RE: what size drill bit for 1/4 20 tap?

ok ok. Who would have thunk that everyone would be soo interested in taps and drill sizes.

I used the 3/16 and it worked like a charm. There are many times where I tell myself, its a model airplane, not the space shuttle so just make it work and save yourself some time and money.

Thanks again,
brian
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Old 02-13-2004, 12:58 AM
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Default RE: what size drill bit for 1/4 20 tap?

Quote:
ORIGINAL: themanimal

There are many times where I tell myself, its a model airplane, not the space shuttle so just make it work and save yourself some time and money.

Yeah but why not spend the time and do it right, then having to spend time again fixing what wasnt right the first time?
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