NPT - NPS Rethreading

[jpthorpe1041]

I have an SL10 and a bunch of fittings that come in as 3/8 NPT and I need to rethread them to 3/8 NPS. Whats the best way to go about this? I have just put them in a round collet and just recut the threads but its pretty ugly and the threads are miserable. Only other idea I could think of would be to use a hex collet and line the threads up but I didn't know if you could make the spindle stop in the same place each time? Well any thoughts would be helpful, thanks for your time - James

[KenFoulks]

What type of NPS thread are you trying to cut?
Are you turning the part first, to take out the taper?
What material is it made of?
What RPM are you running?
What style insert are you using?

[jpthorpe1041]

It is going to be 3/8-18 NPS
We did not cut the taper off first
it is made of hardened steel
and we are using hertel carbide npt threading insert

[KenFoulks]

NPSC, NPSM, or NPSL?
Can you upload a before and after picture?
What RPM did you use?

[KenFoulks]

Forgot one: SPSH?

Also, internal or external?

[KenFoulks]

Does your lathe have M19 spindle orientation option?

[gizmo_454]

I am not sure if this is even possible, assuming you are OD threading. Correct me if I am wrong, but if you have a part threaded with NPT, both major diameter and pitch diameter at the small end of the thread will be too small for NPS. At least, for the first few threads.

I would venture to say that you MIGHT be able to turn NPS into NPT, if and only if you can get the machine aligned correctly to pick up the thread in the right place. But going the other way, I just don't think it will be ok, assuming you are OD threading. Again, please correct me if I am wrong.

Mike

[legmt]

James to pickup a thread on cnc is easy if you think about it. Even Pipe thread..Set RPM to about 50. Pick your Z start point and set zero.. Set X point away from parts as not to touch it with tool... Cycle start ,,let machine turn a few Revolution until you are about half way finished Z travel... Hit Emergency stop... Set or record Z position, Use jog handle to move tool into groove as good as you can get it, and record Z position... Now the amount of Z movement since emergency stop action has to be either subtracted or added to starting point,, and the rest is X axis movement... Simple,, I can pickup a thread in about a minute or so.. And remember to just sneek up on the x...And don't forget most important part,,, the amount you add or subtract from your z start point has to be added or subtracted from total length.....
LEG

[jpthorpe1041]

To answer questions:

External threads
tried at 200rpm
The m19 - says I have it but it won't let me activate it
and the small end of the threads will be cut off so it doesnt matter the beginning of the thread is to small.

[jpthorpe1041]

legmt - that makes a lot of sense I knew that there had to be soemthing along those lines you could do. The only thing is you would have to do this for each one right? THats why i wanted to get it in th ehex collet and stop it in the same spot every time.

[legmt]

James it makes no difference what collect you put it in... Doing it in a hex collect,,, You would have to get length and thread start point the same on every part anyway.. So you might as well forget about the collect and just use the thread pickup routine, On yeas, every part...