The attached pic is a view of an air motor to drive a lathe turret. The two screws, marked, are four inches apart. The section is three inches high.

The airmotor is just an armature with the steel cross-slide block seving as the housing. There is some room for metal removal here.

Is there any chance of finding a servo motor this small? What would be a good vendor? It only has to turn a turret and there's a huge gear reduction. I have no clue how to calculate the torque requirement.

Karl

The break-away torque can be measured if you can attach a lever or some means of a attaching a spring scale and pull the scale until movement is apparent and note the scale value and then calculate the oz/in from the length of the arm, hopefully there is some practical way of attaching an arm etc?
Al.

I could do that once I disassemble the whole unit. Big job. Right now I'm just trying to decide if I should rebuild a worn out air motor turret index unit or try a redesign. Is there a good selection of servos that will fit in a tight spot like this?

Karl

I don't know the cost factor but for compact custom design the frameless motor is pretty compact. http://www.aerotech.com/products/motors/s.html
Down to 50mm.
Al.

this is the kind of motor that maxon or micro-mo would make. www.maxon.com or www.faulhaber.com

Both companies also supply gearboxes.