Triple threaders

[Paul in OKC]

Well, with all the talk of the triple start thread buy lately I decided it was time to play. Having more time than money, and access to my work machines, I made a three start tap and die. 'Tap' is from a piece of drill rod, die is from some heat treated 4140 scrap. Both heated red hot and dropped in oil. Size is 1/2" by 8 tpi, triple lead basically 24 threads per inch. Advances 1/8" per full rotation. Practice material is basic plastic for the die threads piece, and what I believe is hard rubber from one of my bowling ball experiments. This the second attempt. First one the tap worked well, the die was split and as it was tight I expanded it and snapped it in two. No question about hardness! Anyway a fun experiment. Now to get after the pen! I took a gamble on my sizing and did not split this one, although I drilled and tapped it and will use a small cut off wheel if I need to. But first shot is a good fit.

 

[Curly]

Bummer about splitting the split die.

I remember reading that after quenching you can temper the steel by putting it in a 400F degree oven for about an hour. Maybe worth a try especially if it could help stop the cracking.

Did you use manual machines or CNC to make the triple starts?

 

[Paul in OKC]

Did them on a manual.

 

[Curly]

Indexing off the chuck jaws, a gear at the other end, or another way? I haven't tried to single point a thread on the lathe much less a triple start. So far just taps and dies.

 

[randyrls]

I remember reading that after quenching you can temper the steel by putting it in a 400F degree oven for about an hour. Maybe worth a try especially if it could help stop the cracking.

Yep; Steel that is hardened is like glass until it is tempered. The physics reason is that quenching "loads" stress into the piece. Tempering releases the stress, but can change the dimensions of the piece as can quenching as well. An extreme example of internal stress is a Ruperts Drop

Paul; That is an interesting experiment!

 

[Paul in OKC]

My first tap I threaded between centers and used the drive dog to index off the chuck. Worked well. Second one just turned the compound to zero, parallel to the axis, set the lathe to 8 tpi, and moved it the amount for a 24 pitch thread (.0417, or as close as possible) for both the tap and the die. Ran the threads a little over on depth. The internal was tough because of tool size. I had tried to grind off a tap to one 'tooth'. Fortunately we have a very small indexable threaded at the shop.
If you would like to do some, I have a formula software I use at the shop that gives ID and OD and thread height and pitch info. PM me for any size and I can give the numbers.