Thinking about this as an electrical engineer, I'd say don't use DC. DC current is as you say blocked by paint and oil films. Use AC. I think a low radio frequency. Then the DC insulators would act like capacitors and pass AC. even while blocking DC. To detect contact use an AC voltage sensor, typically a diode and small capacitor.
I don't know if this is done commercially but the AC method should in theory by MUCH more reliable. You can even use very long cables if you use strong filters tuned to the frequency. Notice how well the current passes from an AM radio station to your radio even over a miles-long air gap. My guess is that a 100 KHz signal would go right through paint. On Sat, Feb 16, 2019 at 9:46 AM Gene Heskett <[email protected]> wrote: > > Greetings all; > > I've just found that because everything it painted before assembly, > apparently including the inside of the spindle motor mount, that a > ground to the bed frame can be anywhere up to 2 or more thousand ohms to > almost anything else on the 6040, and apparently even includes the > spindle bearings as part of the first 50 or so ohms. > > The net result is that using the workpiece as one contact, the the tool > in the spindle as the other for the alignment function is fraught with > enough variables I could break a tool against the edge of the workpiece, > even damaging the workpiece, before a contact is detected. Since there > isn't Z room enough for one of those $65 spindle mounted contact > detectors, and it would take at least ten feet of ground braid strung > thru the cable chains to arrive at a decent ground on the motor housing, > which wouldn't solve the problem entirely because of the oil film in the > spindle bearings, how the heck do I arrive at a reliable connection that > only responds to a contact between the tool and the workpiece? > > A flying ground lead one could bring up and clip onto the tool would > probably work, but sure resembles something Robe Goldburg would dream up > as it would need to be long enough to reach the tool regardless of where > it is on the table. > > That, or using a much higher voltage limited to a few microamps so as not > to constitute a shock hazard. But basically use it to measure the air > gap. I could make that work even before a physical contact was made but > thats not a tasty idea in the long view either. > > Any other ideas out there? Hopefully something that doesn't involve > changing tools to use. > > Thanks all. > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
