Worm gear for a homemade rotary table

If you drove with a stepper motor rather than a hand crank, you could program in a nice round number for your gear ratio. At eight microsteps/step it would take 93 microsteps to move the table 1º. Actually 93-1/3 so you would never be in error by more than 12 seconds of arc.

An Arduino, a stepper, driver, and a power supply and your set. If you picked your parts carefully, it could be done for less than $50.
 
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One could cut a spur gear with 40 teeth for that 40:1 ratio, but I doubt it makes any difference in the universal world of mathematics. Multiples with more prime factors will give more flexibility. 21:1 is 7*3*3, which does not have a 2*2=4 factor. That will limit you for sure, but 12:1 or 20:1 or 24:1 sure has a lot of workable indexing options. Any ratio that goes into 360 evenly (1, 5, 30, 40, 180, whatever) is a good candidate for a simple degree wheel RT, without need for indexing plates.

I think the backlash compensation scheme on my Kamakura RT would work well against that worm gear. The gear would be bored and shafted on one side to work your handwheel. Against the opposite side, a simple plunger and spring would force the worm gear toward the handwheel side to squeeze the backlash out of the gear pair. You'd have to look at some pics of various RTs to make sense of what I said, but I think those parts are suitable for it if the OP were to pursue the idea further.
 
Why not just buy a 40:1 ratio set of worm and gear from your local bearing house or online stock gear source?
 
The worm gear was just something I remembered I had after robbing parts off the old blower. I do actually have a box of stepper motors and a couple of arduino kicking around
 
One revolution of the worm advances the gear one tooth. 21 teeth so 21:1. That would be an odd number for an RT. Also an RT usually has a mechanism for taking up any slack to reduce backlash. This would be hard to accomplish with your gear set. However, if you are willing to do the math and only turn the table in one direction for its final setting, it could work.
I'm pretty sure it's 22 teeth, not 21 (counted twice, just to be sure). Nevertheless, it would still be an unusual number for an RT.
 
I've just pulled the trigger on a 3 axis DRO for my mill. Aliexpress 11-11 sale.
Should I decide to proceed with the rotary table it should help out a little. But on the flip side it might make necessity a little less.

Before I had the lathe I thought I knew of a million things I would make if only I had a lathe. Got the Lathe and thought seems everything I want to make on the lathe would be better if only I had a mill... now I'm stumped. Seems the only things I can think of to make is more tooling for the lathe and mill. lol I'm soon gonna have to show the wife these things are useful
 
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