Hi Russ

The question of brakes on servo systems is one that has a number of solutions that have evolved to suit different applications. For some the use of the commercial friction brake is not viable either on the grounds of cost or weight. A simple low cost 'brake' can be provided by a relay or solid state switch to short the windings. This is not perfect as there will be some movement. The movement is less than half the full step angle. The application of a steady DC supply has also been used where for safety reasons the stepper has to be removed from automated controls for safety reasons. Both the application of the short circuit condition or the use of a steady state DC supply could obviously be interlocked with the machine guards for additional operator safety.

The application of DC to the windings of an AC motor woll bring it to rest but offers no motion resistance when the spindle has stopped turning. This is often used where there are high speed fans with air filters that need to be serviced but when removed leave the blades exposed. A simple rectifier and interlock switch does the trick for these types of application and depending on the type of spindle motor might help with rapid tool changes.

I have tried to find out more about the motors you have and think they are 200 steps per rev. You might like to try connecting all the motor leads together and try and rotate the spindle as this may well be enough to stop the ball screw rotating under the static load.

Hope this helps keep it simple. On very big servo systems in addition to a brake there is often a pin that is inserted to make sure there is no unwanted motion when the drives are being serviced. The safety pin being sized to cause the drive components to fail but leave the load suspended safely. I raise these alternatives as there are a lot of simple servos out there that might be candidates for a retrospective mod.

Regards

Pat