I'm looking at options for a 4th axis for a small mill (Novamill). I have a cheap belt driven one but the holding and resolution are not great.

So that leaves a modified worm driven rotary table, servo with brake or a harmonic drive.


I also want it to have through hole capacity and use both collet and chuck options. 100mm max. diameter. and be capable of gear cutting

My initial thoughts are:

1. Worm dive is simple but have to live with the backlash and have to adjust periodically.

2. Servo motor and brake seems quite simple and would be good resolution and accuracy. brake can hold for indexing or fixed milling but dynamic milling
would be reliant on the servo holding torque

3. Harmonic drive, Good accuracy and torque but heard that they are prone to damage and can flex out of position under load.

What would be the best choice for good resolution and holding force?