The Home Machinist!

We had to make some acme thread nuts today, Thay were 1 1/4 5 tpi by 4 inch longin cast iron. As the tap took 2 weeks to get and cost was almost $200.00 I didnt want to hurt it so I put a .100 round nose top notch insert in the boring bar and roughed the thread to about .060 deep (full depth is .100) as the nut was a 1/2 inch longer than what the tap was built to cut I wanted to reduce the tapping load as much as possible. Then I got out the bacon fat and tapped the hole, removed it from the lathe....The part was junk....I forgot to say that this a 2 stage tap, The first part of the two stage is the roughing tap and the cutting edge is more like a vee tap than a acme so when I roughed the thread that was a sqr. shape
It was out of time as the tail stock pushed the vee thread to the front shoulder of the sqr. thread, as the tap pulled though it stayed out of time the full lenth of the nut. On the other nuts a roughed with the round incert to .050 and then swithed over to a vee shape. Then the threads of tap dropped in to the vee threads I had roughed and stayed in time...Phil in Mt

The main thing is that you learned.
Just done an ACME internal thread today myself. The 1/2"-10 nut that adjusts the stroke on my Atlas shaper. It had a bunch of slop in the thread and was knocking a bit so it was definitely time for a new one. No ACME taps available so I roughed it out of a piece of 2" dia bronze and single point screw cut it. I had to make a tool up out of drill rod and harden it, but it's all finished now with no discernable slop on the screw. Hopefully its cured the knocking.