A while back someone mentioned that they would like a spindle lock on the SX3. I too thought that it would be a nice improvement. I was mainly interested in being able to lock the spindle for scratch engraving. I wasn't so much wanting a brake that could be used to slow the spindle to a stop. I think that could be better done with dynamic braking and would require a relay or two.
Following are a couple of pictures of what I have done and one drawing.
OM