I've been designing a small-ish 5axis based around a bt30 spindle driven by a 2.5hp servo for a little while now. I have already acquired some fairly beefy used Harmonic drives for the 4th and 5th axis and I am having trouble figuring out if it is necessary to incorporate a holding brake.

Since they are supposed to be zero backlash I don't have the need for a holding brake to reduce chatter. If the cutting forces are high enough to require a brake, I would probably already be at the point of damaging the Harmonic drive. At least, that is what I am thinking. Am I completely off?

Here are some specs of the stuff I've already picked up for reference:
10k BT30 spindle
1.8kW Servo for spindle
CSF-40-50 for the 4th axis
CSG-32-50 for the 5th axis

I have zero practical knowledge when it comes to these Harmonic drives.