How did it end up working out? I have this imperceptible jump when I'm threading. Installing new lead screw and half clamps. If it solves it I'm going the DRO route. Thread on threading issues on G0709.
https://www.hobby-machinist.com/threads/grizzly-g0709-threading-problems.88801/
I don't look at the DRO when threading because I use the compound for each pass, not the cross feed. My DRO is on the cross feed and longitudinal feed, no readout on the compound.
I'm a 29.5 deg. guy (or a pinch over 60 deg. on the Grizzly because of the different coordinate system). I start by cranking the compound back to ensure I have enough travel to complete the thread. I can't recall ever making a next pass with the compound and discovering that the compound was extended out and ran out of travel, but that's because of always starting the compound turned back. Then crank forward on the compound to take out the backlash and Zero the compound.
Next, I advance the threading tool on the work until it just touches. Zero out the cross feed. Back out the cross feed one turn and crank the longitudinal back past the start of the thread. Turn the cross feed in a turn to zero.
Also on the initial set up, the thread dial indicator is swung into the lead screw. I usually just stick with "1" as my target and stay with the same number. For the first pass, I'll jog the lathe until the number is just short of coming around. The spindle is stationary at this point, move the longitudinal crank away from the headstock until I see the number and engage the half nuts. If I went a little past the target, move the carriage toward the head stock to hit the number as long as the tool isn't on the work. Lightly crank the longitudinal away from the headstock to check for backlash in the half nut and ensure I'm actually on the target number. Turn on the lathe and make a scratch pass.
If it's an oddball thread or metric that requires leaving the half nuts engaged, I'll kill power well short of the mark and either jog or manually turn the chuck to the end of the thread. Back out the cross feed a turn and reverse the spindle back to the start of the thread.
If I disengaged the half nut, I'll back off the cross feed a turn, crank back to past the start of the thread (lathe off), turn the cross feed back in a turn to Zero, advance the compound for the next pass. Then either jog the lathe to get the thread dial number to come around or move the longitudinal until the number comes around and reengage the half nuts. Power up for the next pass.
I also NEVER disengage/reengage the feed reverse lever as this sets up the spindle relative to the lead screw. If the feed reverse lever is disengaged and the headstock turns at all, you'll split the thread.
Bruce