Thanks for all the responses. To clarify what I'm doing: I had set the
gain on the servo to give a maximum feed rate of 1/2" / second, with a
10v input. I have an op-amp controller feeding the servo 0 - 10v. But
I can get an out-of-bounds condition where the op amp output is 15v.

So I think that I'll put a 10v zener clamp on my controller output for
the forward feed, but use -15v for the more-rapid reverse.

Bob

BTW - this is turning out very nicely & I expect to be writing it up for
the DropBox.