I'm in the autobody repair business and as far as I know most of the airbag impact sensors on cars that are in the front on the frame rails or some times in the airbag controller in the car have very nice gold contact switches.  Usually it is a gold plated steel ball held by a magnet and two contacts about a 1/4 away, so when the car hits something hard enough the ball will pull away from the magent and short the contacts and BAM you have a blue nose.  I think the parts from a sensor should make a nice precise touch sensor.  I will give it a try as soon as I get the mill to that stage.  You can get the sensors from any you-pull-it junk yard place.  I might have a few around the shop.

Interesting idea Dennis, let us know the results when you have tried it.