Chasing Thread on 8L

Is it possible to chase or pick up a thread on an existing, threaded work piece in the 8L? And if so, how is it done - through the conversational thread program ? Tried most of day and was not successful. Tried adjusting the led length and that wasn’t the answer, unless it is a trial and error procedure.

Any suggestions would be helpful.


Welcome to the Tormach Forums!

Unfortunately, there would be a fair amount of trial and error to accomplish this. You would likely need to manually orientate the material in the spindle, to try and line up the start point of the thread. And then match it as best you can in conversational. I would suggest lots of ghost passes while messing with the values in pathpilot. This by no means, would a be a ‘simple’ process.

Thank you, Sam. I thought that might be the answer.

Thread timing is simple on a CNC Machine. The start point and spindle are timed to repeat tool engagement.
Making the thread deeper or shallower has no effect on timing, just depth.
So, set up to cut a thread.
Use the slowest speed possible - 180 RPM. Turn off the coolant in the program so you can see.
Clean the guard so you can see.
run the thread cycle and watch closely. Unfortunately you can not pause mid cycle. I tired. (I did hit stop and it appeared the spindle and tool stopped a the same time - need to do a real test to see if it is accurate)
If the pitch is .0625 (16tpi) and the tool is about 30% to the left then change the start z position about .020.
Cut the thread with small DOC. Watch to see which side of the tool the 1st chips form and how close the the other side the tool is. Stop the program. Adjust the starting point to center. Run it again. (rinse and repeat sort of)

You should be able to chase the thread reasonable quick - maybe 3-5 false starts. Likely the same speed as on a conventional lathe once you get the hang of it.

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Thank you, Tom for the suggestion. I will try that in combination with Sam’
s suggestions of ghost passes.


Place another piece of stock in the machine. Run the threading toolpath just long enough to see the cut thread. Look at the piece and find the exact spot the thread ends. Place that spot straight up in the chuck. Remove the stock and place the part to be chased. Align the end of the thread in the straight up position. Reset zero on the end of the stock. This will be as close as you can get with the eye to the same clocked position. Put a large positive offset in the x column offset and run the tool path. You may have to adjust slightly clockwise or counter clockwise to match the tool with the V of the thread. If you had a manual lathe I would suggest using that.

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That is an interesting approach. I’ll give it a try. Thankyou for the response.