How to dial in a threaded part?

I just lean a 1/2" X 12" flex scale against an undamaged section (if there is enough exposed), then toss an indicator to bear on the scale right at the point of contact between the thread and scale. Can't go too many revs before the scale walks away, but you can go one turn forward then one turn back. If it becomes a problem, a properly placed mag base will hold the scale.
 
What is often called "picking up" an existing thread for single pointing. Indicating it is easy as mentioned above by using an indicator point that will span the lead of the thread.

Picking up a thread is a last resort.

Once indicated the more difficult task of placing the tool in the correct position with the lathe gear train begins, this will be far more annoying.
 
All good info. As far as repairing/following an existing thread. I would set the compound at 90° or parallel to the work. Move the compound until tool bit is dead center in the V of the thread. Then on each pass just dial in more cross feed…Dave
 
chips&more said:
All good info. As far as repairing/following an existing thread. I would set the compound at 90° or parallel to the work. Move the compound until tool bit is dead center in the V of the thread. Then on each pass just dial in more cross feed…Dave
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With a lathe that allows turning the chuck by hand after engaging the 1/2 nuts just engage them and turn the spindle by hand until you reach the thread,, crank the cross feed in then adjust the compound until the tool is in the center of the thread.

If not turn the spindle on, engage the 1/2 nuts then turn the spindle off and adjust the tool with the compound,

This is not so easy with a machine that has no gear train and can not be stopped without losing position, if you have an easy way of doing so please let me know what it is.
 
I engage the half-nuts, let the lathe coast to a stop somewhere in the range of the threads, then with the threading tool loose, push it into a good thread if there is one, or pick the best spot, then snug the toolholder screws. Back out a bit and tighten the screws. Seldom is this more than a couple of thousandths out. Same basic method with internal threads; engage the nuts, stop the spindle and with the threading bar loose, push it into the thread then hold it in the toolholder until you get it locked down. Of course, on an internal thread you have to make sure you have enough bar hangout, but not excessive.

CNC is a different story.
 
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