NPT Internal Threads

[Vinny]

Proxxon doesn't list one available for it, I don't know if you can adapt another one to it. I know for a metric lead screw there are different dials and for cutting imperial threads you need to leave the leadscrew engagled all the time anyway.

For this job you'll need to keep it engaged, but when it comes to the end of the cut you can turn it off and let it coast since there won't be anything in the way. Then you can kist turn the chuck to move it back to the beginning. At 11 /12 or 12 TPI, turning the chuck by hand will still move the carriage pretty fast.

[Wongster]

I'll give it a shot. Just watched Tom's video on thread dial. Great explanation. Another video showed threading with the lead show disengaged at end of every cut. He marked the positions of the spindle, the leadscrew and the position of the carriage to return to at every start of a pass.

[Wongster]

My first successful internal thread! Lol. 12 TPI straight. The tapered pipe ca still be screwed on smoothly. A bit tight when reaching the end.

[Vinny]

YAY!!!!! We knew you could do it!!! So 12 ended up close enough to 11 1/.2?

[Wongster]

Yes sir, it's close enough to screw smoothly onto the male thread.

I took all the measurements from the sample given to me, no knowing how deep to cut or how big the bore should be. The measurements from the sample don't seem to match anything from the chart I found online. So I just test when I think it's deep enough. But for other sizes, I've nothing to test on.

[Mayhem]

I use a program called ME threads, which gives you the minor diameter and all the other associated values for most thread types.  

   

You can look all this up in Machenerys Handbook but I find it quicker and more convenient to do it this way.  The computer in the shop is always on.

It seems like you have to pay for the most recent version, so I have zipped up and attached the exe file for the version I have below.  This version was a FREE download whenever I downloaded it, so I don't think I am doing anything wrong by attaching it.  However, feel free to remove it if needed.