Making Round Threading Dies

[old toolmaker]

I am making a 1" O.D. 3/8-20 L.H. die. The only commercial dies I could find are made to order and cost $90. The basic die dimensions are found in Machinery's Handbook. The first 2-3 threads are to be tapered and form relieved behind the cutting edge to provide graduated cutting action until it reaches full depth. I am planing to cut the form relief on the lathe using a milling spindle mounted on the compound with tapered cutter similar to a 60 degree countersink. After heat treat I will sharpen using my Quorn and a mounted point in the 4 holes.
My question is: Is there a better way to provide the form relief than what I have planned?

 

[Bill Gruby]

I will definately be watching this one.


"Billy G"

 

[4GSR]

Got to ask, what in the world uses 3/8-20 left hand thread on it?

 

[francist]

Woodworking handscrew clamps, for one.

-frank

Edit: oops, 3/8" - 16, sorry

 

[mikey]

Could you bore a taper with your compound?

Odd thread - could you not screw cut it on the lathe?

 

[old toolmaker]

Got to ask, what in the world uses 3/8-20 left hand thread on it?

I am extending the cross slide travel of a mini lathe having an imperial feed screw 3/8-20 L.H. The new feed screw will be longer than the original (9.5" overall with 5" threaded). I will screw cut it in the lathe between centers using a steady rest and just want the die on hand in case I get a little taper and need to size it. I may never need the die, but it would be an interesting little project.

 

[old toolmaker]

Could you bore a taper with your compound?

Odd thread - could you not screw cut it on the lathe?

Yes, I can bore a taper with the compound but that will just give me a taper. I want to provide form relief behind the cutting edge on the first three threads. If you have one, just take a look at a split round adjustable die and you will be able to see what I am talking about.

Dick

 

[mikey]

Yes, I can bore a taper with the compound but that will just give me a taper. I want to provide form relief behind the cutting edge on the first three threads. If you have one, just take a look at a split round adjustable die and you will be able to see what I am talking about.

Dick

Hi Dick,
I have Mohr button dies and I don't see a relief behind the threads. Here is a screen shot of a Mohr die:


Looks to me like they simply ground a taper. Not sure if I'm seeing what you're seeing, though.

 

[chips&more]

I would make the thread with a follower right on the other side or all around in front or back of the 60° tool bit. Both following together. And both on the tool post. The tool bit would advance on its own translating set-up and not with compound or cross. With this method no taper in threads. And work is not between centers. Good Luck…Dave.

 

[old toolmaker]

Hi Dick,
I have Mohr button dies and I don't see a relief behind the threads. Here is a screen shot of a Mohr die:

View attachment 257776
Looks to me like they simply ground a taper. Not sure if I'm seeing what you're seeing, though.

I think I can see the form relief in your picture if I look hard.
Here is a picture of a Greenfield die I have. I think you can see what I mean from this picture. It is a little more pronounced than the tap you have.
Dick