# Thunder Laser - Chuck Rotary with Lightburn - HELP

Hi - I have a Nova35 Thunder Laser. I use Lightburn. We are trying to setup our chuck rotary attachment. What should the steps per rotation be ? Does this ever change ? We set our circumference of our object which was a tumbler cup with a 4" circumference. At 12,000 the design was stretched too much. We set it to 8,000 and it came out perfect. We then put a 3" tumbler in to engrave, set the circumference to 76.2mm, using 8,000 still and the design was stretched again. I am confused.

With a chuck rotary, the steps per rotation value should never have to change. However, if your tumblers are tapered, you would need to set the circumference for the point you’re engraving at, because it will affect how far the surface needs to travel.

Also, you said 3" tumbler, and then you said “set the circumference to 76.2mm”. The diameter of a 3" tumbler is 76.2mm, but the circumference is 239.4mm (diameter * Pi). If you used the wrong number that would certainly make a mess of things.

Haha oooooppppseeee YES that part makes sense !

Is there standard steps per rotation that we should use for the chuck or do we need to play with it ?

There’s no standard - It’s motor steps x micro-stepping x gear reduction on the rotary, and all of those can vary between machines. Motor steps is almost always 200 or 400, so the steps/rotation number is usually a nice round number, but it doesn’t have to be because some rotaries use weird gear reduction numbers.

Draw two horizontal lines “circumference” millimeters apart, like this:

Run that on the rotary - If you have your steps count correct, the two lines will overlap. If the 2nd line falls short, you need to increase the step count. If the 2nd line goes past the first one, you need to decrease it.

So in short play with that number ?

Edited my post above - yes, trial and error is usually the simplest way to figure it out, but you only need to do it once.

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