The paper trick, often referred to as using cigarette papers (they're thin, uniform in thickness, and were in everyone's pocket at one point), is the most common way to do touch-offs (the official name for this action).
If you need more precision, there are electronic devices (as mentioned) and there are also rigs that use a dial indicator. The latter can be built if you have a spare indicator (there is a nice bit about how to do this on the Industrial Hobbies web site), or you can buy a handy little gadget to do it that is built into a cube exactly 2" high. You move down until the need moves, read of the value, and the offset is exactly 2.<value>". You can set the little cube atop your workpiece or the machine table depending on what sort of offset you're trying to determine.
eBay seller 800watt offers these little cubes on eBay for circa $30. Just do a search on "presetter" under the Business and Industrial category and you'll see a variety of such things. Auction #140026272002 is one such. Just put that auction number in the eBay search to see it.
A related approach is to preset the tooling in the holders at a known height, use the tool offset table in your CNC software, and just tell the program the known height. You can either measure the heights with a height gage, or buy a tooling system from an outfit like Tormach that offers a system designed to keep them all at the same height.
So there's really two issues. One is finding "Work Zero" and one is accounting for different tool lengths. You're CNC software will let you attack these separately (nice if you have multiple tools that want to run quickly for production) or treat it all as one event.
Best,
BW  |