Z axis servo brake failure

**srcarr52** · 10-13-2020, 11:15 AM

A few weeks ago my Z axis stopped moving, the brake was no longer being released. After probing wires I determined that the windings inside the brake had failed as it was an open circuit.

Sorry I didn't take any pictures of the servo disassembly but the brake is bolted to the mounting plate of the servo motor. Remove the 3 allen head screws in the center circle and the 4 5/16 head nyloc nuts and pull the bottom plate off. Then use a small gear puller to pull the bearing as it's a slight press fit onto the shaft and then the brake will drop out.

Since the bobbin for the windings is glued into the brake I had to machine a new one from delrin.

Then I used my little CNC lathe to wind the 35g wire because I could run it for a set time at a consistent speed to count the windings. My rough counting of the windings on the original was 2800 wraps, but my calculations said I needed closer to 3800 wraps to get the 13w consumption at 90v which should yield 623ohm. I measured the one on my other mill at 575ohm so there is some wiggle room.

I ended up with around 3600 wraps as I stopped early to leave room on the bobbin for the leads which ended up at 585ohm. Maybe 36g wire would have been better but I measured the original wire at 0.0061" which is 35g.