[Cory]

Setting Z offset is much safer if you use a ground pin (.250 and up works great), jog the tool to a height above the part that the pin will NOT fit under, and then attempt to slide the pin under the tool with gentle pressure as you slowly jog the tool up by .001 at a time until the pin can slide under the tool either freely or with light resistance.

You eliminate (almost) any chance of chipping the tool by jogging it into your pin/shim/part, since you are going up instead of down. If you were to jog the wrong way, you have a pin diameter's worth of buffer zone before you hit anything.