Drill Size for 1/4 - 20 Tap?

[ddavelarsen]

Thought I had a table that would tell me this, but if so I can't find it. Any help appreciated!

Dave

 

[simmonsk]

One chart says #9 .1960"
Another says #7 .2010
Enjoy...Ken:barf:

 

[Sylvester]

#7

 

[ddavelarsen]

Thanks gents; two votes for #7 are good enough for me.

Dave

 

[Chuck Gedraitis Knives]

I always use a #6, that way it is a little easier to tap. I hate it when they break off, espically the 1-72 ones I use.

 

[T. Erdelyi]

Here are some links with all kinds of tap/drill charts


http://www.pos.net/reference/tap1.htm

http://www.toolmanmike.20m.com/tapchart.htm

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

 

[ddavelarsen]

T. Erdelyi, thanks for the links. Nice Deadie Bear avatar, too!

The larger hole would certainly be safer, and for my purposes will probably work fine. Thanks again to all,

Dave

 

[tom mayo]

number 7 is the preferred drill.

It depends on what you are tapping. If it is Titanium you might want to make the hole a tad bigger, most anything else I would go with the recommended drill. How deep??

In knifemaking that is a BIG hole........more threads per inch is way better.

 

[Arlee]

that depends on if you are using a cutting or form tap.Cutting taps use a No 7 drill (.201).Form taps make stronger threads but are harder to use especialy in aloy steels and S.S.and use a No 1 drill(.228)they are best used in blind holes where you may have trouble with chip removal or with thin stock less than .125 thk. Because of the stronger thread they produce as the metal is actualy cold forged to form the thread.Also I agree with going over size for the tougher aplications but dont go to large as most drills cut a little big to start with unless you pre-drill with a smaller drill first,and its alot harder to make a big hole smaller than a small hole bigger.
So start with the recomendid drill size in some scrap material of the same stuf you will be using till you get the fill for whats going on.Hope I didn't get to far off track for you.This usually works for me.

Arlee

 

[Dan Gray]

in most sizes
you also have a Class A fit this
fit will need a wrench to put it in all the way.
it has it's places.

 

[ddavelarsen]

Well, I ended up using a #1 drill, the tap just didn't want to start in the #7 hole. I went about 3/8 into the bottom of a SS pommel. All the bad stories I've heard about working with stainless for fittings seems to be true. But the sense of permanence I'm already getting from it far outweighs any adjustments I have to make in the work. If this turns out anywhere near the way it looks like it's going to, I'll be hard to convince to use anything else from now on. Stainless steel is cool.

Dave