I recently upgraded my mill to use Clearpath Servo motors. The motors I used are the CPM-SDSK-2341S-RLN which are 828 oz-in of torque.
The motors run really well. They are powerful enough for the mill, and are absolutely silent when they run – this was really surprising. I’d never realized how much noise the steppers made.
I swapped out 400 oz-in steppers for these servos. Interestingly, when I first installed the servos, they had trouble moving the table. This was before calibration, and also before I adjusted the power supply to output the full voltage (there’s a selector switch in the power supply for various input voltage levels). Once I adjusted the ways, lubricated the ways, and tuned the motors, the mill ran really well. I’ve been able to do heavy cuts and have never noticed an issue. I’ve been able to speed up the “rapid” speed of the mill to 100 inches/minute, from the previous setting of 40.
Teknic states that the servos can be one-half the rated torque of a stepper motor, but I’m skeptical, based on my experience.
The servos each have a USB port, and come with a windows application for tuning the motors. When the application runs, you can see the torque, maximum torque, speed, direction, etc. In the tuning mode, you first define a range of motion for the motors – say a 20 to 50 turn range where the motor can run safely. Then it enters a tuning mode where it applies different levels of torque, moves the mill slowly and quickly in each direction, and does loud jarring movements where the motor slams the shaft. It does this to analyse the resonance of the machine. It is scary to watch. It’s like your mill is being hammered with a sledge hammer! In fact, it loosened the set screws on the Lovejoy connectors (which were too small anyway). The tuning takes about 20 minutes per axis.