Making threading taps and dies

[Wannabe2]

I am interested in trying my hand at making a tap and die and was wondering if there are any rules/formulas available in relation to making them. Some of the things I'm looking for are tap flute sizes and position, die lead-in tapers, die flute(?) position, any pitfalls.

 

[Bernd]

I believe you'll find all those answers in the "Machinery's Handbook". That's a book every machnist should have in is tool box.

Bernd

 

[Alphawolf45]

Harden and temper the tap and dies is of far greater importance than flute size and location or lead in taper......Do a proper heat treating job with it and everything else can be wrong and it'll probably still thread a few holes.. If I bust the end off a tap I grind it back by eyeball and go back to work with it, apparently the form isnt hyper critical 'cause I get reasonable use of some very ugly taps...I made some taps and dies for gunsmith jobs, if I get'em hard enough they will cut.
.

 

[Mcgyver]

Harden and temper the tap and dies is of far greater importance than flute size

perhaps that may be so in certain smaller sizes, but I have to disagree as a general statement. The flute does a couple a couple of things, its placement needs to be off centre slightly to so positive rake is created (if using a ball end mill) but why size is very important is that the threaded area left, after the flutes are cut, has to be relatively small or that tap won't work. There’s no relief on the back of the threads so if you don't minimize this the tap won't turn.

here's one i made where the flutes weren't large enough - wouldn't work

That error was pointed out to me and i re did them with large flutes and smaller thread area and it worked perfectly

Taper doesn't matter imo, look up the tolerances on the mating piece an make to suit, ie tap has to cut a thread slightly larger than the high tolerance size of a male thread.

 

[Alphawolf45]

perhaps that may be so in certain smaller sizes, but I have to disagree as a general statement.

It is hard to make a general statement that cant be countered. I didnt mean too imply that a newb couldnt botch one up too bad to use...But with a bit of effort/experience it aint a tough job is it?

 

[Mcgyver]

...But with a bit of effort/experience it aint a tough job is it?

not unless you get the flute size/placement wrong

 

[Wannabe2]

I get reasonable use of some very ugly taps.

I can relate to this. I made one hugely ugly tap. Didn't harden and temper it correctly. Tried it in aluminium and it twisted. Looks a bit like a twist drill now. Re-hardened it and it did the small job I wanted to do but as a guy I used to work with would say "It's rough but honest".

What I was trying to do was make a few 12-28 gib screw lock nuts that are missing off my taper attachment and since I didn't have a tap or die of this size, was unlikely to need this size too much, I thought I'd have a go at making one. I know I could probably go out and buy one for a lot less than the time I've spent on this but it's all experience.

For the tap I screw cut the thread and taper in the lathe and used a ball endmill to create the flutes. I tried to position the 3 flutes on centre and equidistant. First mistake by the sound of it.
Messed up the tempering (second mistake) and it's very very ugly but it did the job. I wouldn't want to push it too far though.
I then started looking at making a die but wasn't sure about the tapers. Found one site that suggested 45 deg on the stamp side and 60 deg on the back side but on a small die this doesn't leave much left for thread cutting. Wasn't sure about where to position the flutes on the die but you are saying I should be positioning these to create a positive rake.

Mcgyver is also saying to keep the cutting surface small. This is another area I have been going wrong trying to keep it large. Third mistake.