Slotting Saw Arbor for Unimat

[PJs]

Definitely safer...a lot of spun mass there...wouldn't be pretty if something went hinky. Your new arbor is a beaut, and will be much closer coupled than the old way! Thanks for the comparison. ~PJ

[mklotz]

PJs,
The only challenge with cutting metric threads on this lathe is that the split nut has to stay engaged and the motor reversed for each threading pass.

Well, although it's the inherited wisdom, it's not exactly true, at least in some cases. Consider the following truism...

If we disengage the half-nuts and move the carriage a distance to the right that is an integer multiple of the thread pitch AND also an integral multiple of the leadscrew pitch, we can reengage the half-nuts without losing registration on the thread we're cutting.

Such a movement, once calculated can be accomplished accurately in a variety of ways including a DI and a "stick" cut to the correct length working against a stop fixed to the lathe ways.

If you're interested in trying this, there's a program (STICK) on my site that will calculate the required displacement.

Sometimes the required length is too long to be practical and one will have to resort to the "keep the half-nuts engaged" method but when it does work it's a real time saver.

Here's an example output from STICK...

THREAD CHASING OFFSETS

Type of leadscrew thread (M)etric or [I]mperial? I
Leadscrew pitch [8 tpi] ? 8
Type of thread [M]etric or (I)mperial? M
Pitch of thread being cut [1 mm] ? 0.5

Move carriage 2.500 in = 63.5 mm to right to recapture thread