Hi Chuck,
I agree leaving the half nuts engaged is the easiest way to cut threads. I resurrected an old Boxford lathe and installed a VFD driven motor. It has been set up to accelerate and decelerate fairly slowly. This makes it very awkward when running a thread up to a shoulder as the lathe continues to rotate after the OFF button is pushed. It became clear that I needed to disengage the half nuts to stop threading instantaneously. The lead screw is imperial but I cut both metric and imperial threads. I didn't have a thread dial but made one as shown in the picture.
I made it out of PVC as it was only supposed to be a prototype but it worked so well I use it as is. Note that the gear needs to be angled to match the thread angle of the lead screw. I have attached a drawing of it.
I came across this on Youtube which shows how to use a thread dial for cutting both metric and imperial threads.
The procedure is as follows:
After setting the tool to cut the correct depth, start the lathe in the forward direction and when the thread dial reads 1, engage the thread nut.
When the tool has advanced to the end of the thread, disengage the half nut and turn the motor off.
Withdraw the tool to clear the work.
Start the lathe in reverse and when the thread dial reads 1 engage the half nut.
Run the lathe in reverse until the tool clears the work.
Turn the lathe off but leave the half nut engaged.
Set the tool to the new depth and start the lathe in the forward direction.
Repeat till the thread is cut to size.
I hope this is helpful.
Regards,
Alan
