I want to be able to turn the part clamped in the lathe by a fixed and repeatable degree. One way would be to print a scale and glue it to the lathe chuck. Then have a needle point to that scale and move the part by hand, somehow fix the chuck in place, then drill. The "fix the chuck in place"-part of it I will do. But I somehow didn't like the paper scale idea.
So let's take a look at the rear of the lathe. There is the main shaft (that is holding the chuck on the front) sticking out. It has a drivebelt for .. well... so it turns. And it also has a small ringear to drive the leadscrew. I won't go into detail about that. The important part here is, that there are interchangeable gears here, that are driven by the main shaft.
Or we can use these gears' teeth to count degrees. One tooth equals some amount of degrees. There is math involved. Devide 360° by the number of teeth... You get the gist of it.
Depending on the gear used you could, by counting teeth, get a repeatable degree of rotation on your part up front.
Now I had to make two "things" to make it all work.
First a pin to count the teeth and second a clamp so the main shaft wouldn't move while drilling the part.
The "toothlocker" or counter:
Has a wedge shaped tip that is slightly off center. I can rotate the tip 180° to count "half teeth". And its also possible to lock the pin at some distance to the gear to allow normal operation of the lathe.
The shaft clamp..
Total:
And the first test piece:
I can work with that.