Internal threading on a cnc mill

[jime]

Looking at internal threading a .950” hole, about .5” deep. The thread are a very truncated “v”, 20 tpi (looks almost like an acme), the major diameter will be about .962”.

Has anyone experience cutting these on a CNC mill? I was going to make a tap (about $250), but was wondering about doing them on the mill. I have many to do, but over a long period of time. I was wondering which way would be most cost effective.

Jim

[fpworks]

Jim,
Without a doubt, I would certainly threadmill those threads. As long as the threads are still 60 degrees, you could use an off the shelf threadmill for 7/16-20 threads to acccomplish this. I just checked the price at $115.

Threadmilling is also a much more secure process with larger threads, and the threads turn out a lot prettier.

I would imagine that inspecting the major diameter is going to be the expensive part, if you have to buy a gauge...I hope you have a part with the external threads!

Justin

[jime]

Justin,
I've got to turn the shank and thread it on the lathe.
Wouldn't I have to grind the tips off the threadmill to get the
truncated major diameter?
Thanks!
Jim

[fpworks]

Jim...sorry, I didn't think through it and thought your minor diameter was to be truncated.

Yes, you would have to grind the OD of the threadmill. I imagine this would be fairly inexpensive for a threadmill manufacturer, since it would be a modified standard item, and not a full special.

So, your minor diameter is 0.950 and the major is 0.962? If that is the case, you will still have enough thread on a ground down 7/16-20 threadmill.

I've had good luck with threadmills from these guys: www.threadmillsusa.com

[jime]

Thanks Justin, I'll check 'm out.

[machineconcepts]

You can also check out the indexable threadmills, they may offer an insert with the trunification you desire.