Now wait, you can use the thread dial with odd pitch threads[3 1/2 for
instance], as long as you always return to the same number, it makes no
sense to me that metric would be any different.
Second, if you could not do that, could you not put witness marks on the
leadscrew, chuck, and set an indicator or stop on the back of the
carriage, and it would HAVe to be in the same spot, no?

Stan-O wrote:
Tim, one note that you might want to remember on your lathe, it will
make you life easier.

Even though you do not have a thread chasing dial, you can still
dissengage on threds that are a multiple of the leadscrew.

For example if your lathe has 4 TPI, you can thread
4,8,12,16,20,24,28,32 etc and disengage because the lathe will follow
the same path every time you fully engage the half nut.

Your lather probably has 6 or 8 TPI leadscrew so you can figure out
multiples and save you self some time and grief.

-S