Any way to float spindle on Z axis

[henrycopeland@bellsouth.net]

A potential customer here who is presently cutting multiple parts from thermoformed ABS sheets. I had to build a mount that allows the router to float on top of the formed sheet since Z on the material varies +- 1 in(on my worn out CNC that I use now). Each sheet comes from vacuum former different from another in Z height dim. Will I have to fabricate a floating device for Shopbot or is there a height sensor that will work?

[hwd_woodworking]

Why couldn/t you use a large bit and z zero off the table. Once the machine knows where the table is you should be able to cut any sheet. In fact even after you z zeroed off the first sheet don't change the parameters of the bit and don't z zero the following sheets.

If they vary a lot you can have say three different programs one for ~each range of materials. Then when you get it in you would know which one to run by the thicknesses.

[davidallen]

if zeroing from the top of the piece won't work, there are some 'floating bits' around. they're generally used to cut circuit boards and are very small in diameter.

what kind of cuts are you doing.

[henrycopeland@bellsouth.net]

Thanks guys. My sheet thickness now is .110 and will be reduced later. I'm using a 1/4" dia upward spiral at about 55 in/min feed. One problem I have on occasion is a wrincle/fold in the plastic sheet where the vacuum didn't pull down into mold. Instant broken bit if not careful. Also am vacuuming shavings at the bit. A fixed bit height will just not work. Maybe I can rig up an ultrasonic range finder to plug into Z control, we'll see. I have to assume the most stupid will be operating this machine.