Threading Dial Question

[Logan Novice]

The last lathe I had (a mini lathe) had a threading dial that tracked whenever it was engaged with the lead screw.
My Logan lathe has a threading dial that will track when engaged with the lead screw if:
the carriage is operated by hand
It will not track if:
the half nut is engaged
What am I missing here?

 

[RJSakowski]

The threading dial is not supposed to rotate when the half nuts are engaged.

 

[RJSakowski]

OK, an explanation. When the half nuts are engaged, the carriage is tracking the lead screw at the same rate as the thread dial gear so the advance of the lead screw thread is in sync with the movement of the carriage.

When the half nut are disengaged and the lead screw is turning the lead on the screw rotates the gear on the thread dial. Similarly, movement of the carriage will rotate the gear, You can hold the thread dial stationary by manually moving the carriage at just the right speed.

If you think about it, when threading ,as you engage the half nut on a particular dial setting, it holds that dial setting until you disengage the half nut. As you back the carriage to make another passm the thread dial rotates and when you're ready to start the next pass, you wait for the thread dial to hit your dial setting.

 

[benmychree]

And the rule for using the thread dial when threading is:
engage on any line, (including any numbered line) for even threads, engage on (any) numbered line for odd threads. engage in opposite numbers for half threads, and on one number (only) for quarter threads.
Also, if the thread to be cut is a factor of the lead screw, the half nuts can be closed anywhere it will engage. For instance with a four TPI lead screw, the half nuts may be closed anywhere for 2,4,8, 16, 32 TPI, etc.

 

[Logan Novice]

OK ... all of that makes sense. Now it's time to thread the chamber of that rifle barrel. Thank you

 

[RJSakowski]

And the rule for using the thread dial when threading is:
engage on any line, (including any numbered line) for even threads, engage on (any) numbered line for odd threads. engage in opposite numbers for half threads, and on one number (only) for quarter threads.
Also, if the thread to be cut is a factor of the lead screw, the half nuts can be closed anywhere it will engage. For instance with a four TPI lead screw, the half nuts may be closed anywhere for 2,4,8, 16, 32 TPI, etc.

This is not true for all lathes. The Grizzly 602 has a 12 tpi lead screw and for threads evenly divisible by 3, engage on any of the twelve marks on the dial. For half threads (11-1/2, 13-1/2, etc.) any two marks separated by 6 (1,7; 2,8; etc.). For all other threads, marks separated by 3 (1,4,7,10; 2,5,8.11, or 3,6,9,12).