What size stepper motor is needed for rotary axis?

[Dale gribble]

I'm in the process of Building a rotary axis, so my thinking is to use a large stepper motor nema 34. I'm thinking of driving the motor via a 10 micro stepping Gecko as I've had good results on my router motors. I'm re-using a manual table indexer,

My questions are:

What torque motor do I need?

Do I need a brake or will the holding torque of the motor be enough?

If a brake is needed what do you recommend?

Whats the ideal gear ratio or is it min angle per step?

Anybody who can help or has been there and built one your information would be gratefully received.

Kind regards

Dale gribble

[ger21]

All your questions depend somewhat on the answer to the others. First, you need to know how big (diameter) the parts you'll be cutting are, and how much force you need at that diameter. Then you figure out how much torque you need to achieve that, and depending on gear ratio, choose a motor to match.

[Dale gribble]

Thanks Gerry for your reply, what I failed to mention was that, I will be cutting large parts 6" to 8" diameter. Like other hobby builders I'm looking for ball park figures. As i will be cutting parts i haven't designed yet it's hard to calculate to forces needed as there are 100's of variables involved. I have read most of the forum's on rotary axis. But it is hard to work out how accurate these builds are. I built my first router around a year ago now, but if I were to build another one again their is a lots of things I would improve on. I was looking for some insight on thoughts of people that have built rotary tables.

Kind regards

Dale

[vger]

Dale,

I built my own rotary from scratch for use with my router. I used 1/2 10 ACME as worm screw and hobbed my own worm wheel from brass with 180 teeth. That meant with full step (200 steps/rev) I got 1/100 degree steps. I used a small NEMA 23 stepper running at 1 amp and it's durn near impossible to get the table to stall by hand. Of course with 180 to 1 reduction the torque of the motor is multiplied by almost that (minus friction). Using worm drive also means there was no need for a brake.

Steve

[Dale gribble]

Thanks Steve,

My rotary table does come with a worm drive but I discounted it due to it having large backlash, but I can see these have a lot of advantages like no brake and simple design build, I'll see if I can lap my gears to reduce to backlash and maybe spring load the meshing of the gears to eliminate the backlash. Also I realise a don't need such a big motor as I thought.

Kind Regards

Dale