I am trying to thread a 1 inch npt OD thread on the back side of a part since I have a internal thread on the front, to do it in one operation. I only have right hand tools and programed it to thread from the turret to spindle, plunging into the part on the big part of the thread and threading toward the spindle going down in x. The gauge fits fine but the thread looks sloped or angled. Is this because I am not threading from small end to large end on npt thread?
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Npt threading on hardinge 6/45 lathe
- Thread starter Staggs007
- Start date
- Replies 5
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Can you post your code? I have threaded external NPT threads on the back side from the big diameter to the small diameter like you are trying to do, and it worked ok. I don't really know what you mean by the thread looking sloped or angled. What kind of insert are you using?
I can look at my code tomorrow and post it. Basically, the taper has to be in the other direction from a standard tapered thread. Instead of going from small to big in the diameter, you're going from big to small. So, I think your R or I needs to be positive instead of negative.
Also, the threads do get a little cropped when using a cresting insert like the one you posted to do this kind of back side threading. Since the insert is specifically for making a tapered thread, the cresting portion before the V is a little higher than the cresting portion behind the V. It basically follows the taper. The problem when using this insert on the back side is that the taper is going the other way, so the cresting part of the insert behind the V is digging in and over-cutting. For the parts I was making, it was ok. You could see that the threads weren't as sharp, but they were crude parts. It probably wouldn't fly, though, if you were making more precise pipe threads like NPTF where the major needs to be closely held.
Also, the threads do get a little cropped when using a cresting insert like the one you posted to do this kind of back side threading. Since the insert is specifically for making a tapered thread, the cresting portion before the V is a little higher than the cresting portion behind the V. It basically follows the taper. The problem when using this insert on the back side is that the taper is going the other way, so the cresting part of the insert behind the V is digging in and over-cutting. For the parts I was making, it was ok. You could see that the threads weren't as sharp, but they were crude parts. It probably wouldn't fly, though, if you were making more precise pipe threads like NPTF where the major needs to be closely held.