Question on drill and tap

[corvette8n]

I want to d&t for a 2-56 screw, I have the tap but need the drill, my local hardware store was unable to help. What size drill do I need and where can I get it. I an trying to drill a leaf sight which I think is some kind of spring type steel.

[jhrosier]

The tap drill size is #50 (0.070")

http://www.efunda.com/designstandards/screws/tapdrill.cfm

Jack

[Willbird]

The formula for tap drills is not too terrible to remember.

Take the dia of the tap then subract the LEAD from it. IN this case it would be dia-1/56. This is dead easy on Metric taps. M6 x1.0 uses a 5.0mm tap drill :-). For other threads that the size is denoted with threads per inch just divide 1 by the tpi. 3/8-16 then uses 3/8 minus 1/16 ........

Bill

[Junior1942]

"lead"???????

[oneokie]

"lead"???????

"lead" = "pitch"=tpi= threads per inch

[jhrosier]

"lead" = "pitch"=tpi= threads per inch

If you want to get teknickle, the lead is the pitch times the number of starts.
The pitch is always the distance between the individual threads. (TPI.)
The lead is the distance that the thread advances in one turn.
Multiple start threads advance at a rate determined by the product of the pitch and the number of starts.
The only multiple start thread that I recall on a firearm is the safety lever on a Lee Enfield.

Just thought that you might want to know.:coffee:

Jack

[Bad Water Bill]

jhrosier
That was great. Now how about one in metric PLEASE.

[Red River Rick]

Metric is even easier. Major diameter minus the pitch. ie: M6 x 1, 6 - 1 = 5; M8 x 1.25, 8 -1.25 = 6.75.

RRR

[jhrosier]

jhrosier
That was great. Now how about one in metric PLEASE.

:-D Lee Enfields are all inch, not metric.

Sure hope it stops snowing so's I can go shooting. I think I'm getting wacky.

Jack

[Red River Rick]

:-D Lee Enfields are all inch, not metric.

The threads on the Lee-Enfields are British Witworth form threads, yes, based on the inch system but they have a 55 degree included thread profile and not 60 degree like the "Unified" thread.

RRR

[jhrosier]

The threads on the Lee-Enfields are British Witworth form threads, yes, based on the inch system but they have a 55 degree included thread profile and not 60 degree like the "Unified" thread.

RRR

Thanks,
I stand corrected.:drinks:
It is obvious that we all have way too much time on our hands today.:-D

Jack

[Franklin Zeman]

Most taps have the tap size and the required drill size on the shank.

[HotGuns]

Most taps have the tap size and the required drill size on the shank.

I dont think so.

I have several thousand taps at work and none of them have the drill size on it.

[JIMinPHX]

The formula for tap drills is not too terrible to remember.

Take the dia of the tap then subract the LEAD from it. IN this case it would be dia-1/56. This is dead easy on Metric taps. M6 x1.0 uses a 5.0mm tap drill :-). For other threads that the size is denoted with threads per inch just divide 1 by the tpi. 3/8-16 then uses 3/8 minus 1/16 ........

Bill

I always thought that for 60 degree sharp-V thread-form threads you subtracted .866 x pitch from the major diameter, not full pitch. Sine of 60 = .866

Then there are also the little details about cutting 65% threads, 70% threads, class 3, etc.

This is for common cut taps, not roll forming taps.

[JIMinPHX]

From Machinery's Handbook -

[R.M.]

Just Google "Tap Drill Sizes" and there's lots of charts available.