machinist question

machinist question

Nobody
Nobody

July 11th, 2012, 8:07 pm #1

i need to tap a hole for 4-40 screws, but what drill size to clean up the hole do i use? have the tap, but i don't want to put too much pressure on the tap by taking off too much material off with it.
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MarkT
MarkT

July 11th, 2012, 10:08 pm #2

Search for tap drill chart and you can find several answers:

http://www.championscrew.com/form_tap_drill.htm
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sniper1rfa
sniper1rfa

July 11th, 2012, 10:10 pm #3

i need to tap a hole for 4-40 screws, but what drill size to clean up the hole do i use? have the tap, but i don't want to put too much pressure on the tap by taking off too much material off with it.
If it's a cut tap and you're tapping by hand I would go with a #42. #43 through #41 would be acceptable, but a 43 is a bit tight (75%) and a 41 is a bit loose (50%)
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sniper1rfa
sniper1rfa

July 11th, 2012, 10:11 pm #4

Search for tap drill chart and you can find several answers:

http://www.championscrew.com/form_tap_drill.htm
that chart is for form taps, not cut taps. Those holes will be far too loose for a cut tap.
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sniper1rfa
sniper1rfa

July 11th, 2012, 10:13 pm #5

If it's a cut tap and you're tapping by hand I would go with a #42. #43 through #41 would be acceptable, but a 43 is a bit tight (75%) and a 41 is a bit loose (50%)
Rather than the wire-size drills you could use a 3/32 which is basically identical to a #42.
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Nobody
Nobody

July 12th, 2012, 1:22 am #6

this is for a quick and dirty little project. i am no machinist, and was looking for a drill size, preferably in standard that i can drill out the hole, then run the tap in by hand. the #41 or #42 meant nothing to me. its a one end tap(taping one side of a through hole), so i didn't need to get a bottom tap or anything else than the taper tap i have.

3/32nds, i think i can find a drill bit for that.
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Nate
Nate

July 12th, 2012, 7:32 am #7

If it's a cut tap and you're tapping by hand I would go with a #42. #43 through #41 would be acceptable, but a 43 is a bit tight (75%) and a 41 is a bit loose (50%)
Until today, I had no idea what form tapping was, and thought it was only possible to do external threads through forming methods. I have so many things to read now...
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FireFrenzy
FireFrenzy

July 12th, 2012, 12:25 pm #8

the "drop everything you are doing to help out with someone elses project" thing...
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sniper1rfa
sniper1rfa

July 12th, 2012, 10:35 pm #9

this is for a quick and dirty little project. i am no machinist, and was looking for a drill size, preferably in standard that i can drill out the hole, then run the tap in by hand. the #41 or #42 meant nothing to me. its a one end tap(taping one side of a through hole), so i didn't need to get a bottom tap or anything else than the taper tap i have.

3/32nds, i think i can find a drill bit for that.
Wire sizes, letter sizes, and fractional sizes.

Wire sizes typically start at 80 and got to 1, increasing in size with decreasing number. A #80 drill is 0.0135", and a #1 is 0.228".

Letter size drills are A-Z, and pick up where the wire sizes left off. "A" is 0.234" and "Z" is .413".

Fractional sizes are just that - fractions of an inch, in steps of 1/64". Fractional sizes start at 1/64" and go to whatever the biggest drill you can imagine is.

Drills smaller than the smallest wire size are generally just spec'd out in decimal-inch and are generally hard to find through custom order.

It's common to see drill indexes sold which have all three types of drills in one case, such as the one here:http://www.amazon.com/Steelex-D1137-Dri ... B0000DD1VS







Metric drills start at some fraction of a mm and carry on up through some large number of mm. It's a lot simpler.
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sniper1rfa
sniper1rfa

July 12th, 2012, 10:37 pm #10

nt
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