On Monday 18 February 2019 02:31:46 jrmitchellj wrote: > Perhaps victims of the Trump tariffs! > > --J. Ray Mitchell Jr. > jrmitche...@gmail.com > > > > "No problem can be solved from the same level of consciousness that > created it"Albert Einstein > > On Sun, Feb 17, 2019 at 4:00 PM Gene Heskett <ghesk...@shentel.net> wrote: > > On Saturday 16 February 2019 20:01:38 Gene Heskett wrote: > > > On Saturday 16 February 2019 14:28:33 Chris Albertson wrote: > > > > 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. > > > > > > The disadvantage there is the rc charge time. This means among > > > other things a relatively leasure velocity to the first trip, and > > > a much slower 2nd approach, where as in using the dc circuit, one > > > usually uses a rotating with the spindle probe so even if it has > > > some runnout, the contact surface is recorded an by the first > > > contact discharging a .1 ufcapacitor, which takes long enough to > > > recharge that the contacts logic zero, is captured and reported to > > > LCNC instantly even if by the time the servo thread actually reads > > > it, the contact has been lost again for .9 milliseconds. The rf > > > circuit, cannot possibly respond in that time frame unless the > > > closing velocities are also very slow. The DC method is inherently > > > the faster method, but does require a very low ohmage connection > > > in order to fully discharge the cap on a 10 microsecond contact. > > > And we definitely DON'T have a low resistance circuit on this > > > machine. > > > > > > I have one of this old tony's contacts about 75% made, but out of > > > a brass tube instead of a steel probe and I'll take the machine > > > out of it by grounding the workpiece, and wiring the tube straight > > > to the probe input, using the same old cap for storage. The brass > > > is long enough it can hit and be bent 1/4" without damage as it > > > will just spring back. > > > > > > But its been a long day today. I'll figure out something thats > > > hopefully repeatable. > > > > Got that done, almost worked when using brass against the edge of > > this alu panel, so I thought I'd get fancy, and found a steel sewing > > pit with the rounded backend sewing pin and soldered it into the tip > > of the tube. Disaster, I can see it sliding along on jerks as I run > > it back and forth touching the edge of the alu, but the only place > > its making actual contact is where the brushed finish is damaged, > > anyplace else needs a 10lb push with my finger to break thru the > > aloxide and actually make a contact. Would probably work with most > > anything metallic except the alu. To do this would need a 1kv > > supply, limited to 1 microamp so as not to eat up the probe too fast > > and measure the voltage electrostaticly. > > > > Last week there were at least a dozen guys selling imitation > > Reneshaws for 69$/copy. But I'll be darned if I can find one on > > fleabay today.
Finally found one and bought it. They sure are BIG though, 2.1" in diameter and 4+" long. And Z motion is certainly limited with that installed! Bought a t.l.o. setter and a big bag of teeny homing switches. This thing has blocks of solid cambric for crash stops, looks like a 2.5mm thick switch glued in there ought to make a serviceable homing switch. Now we sit and wait, bored out of my skull till stuff gets here. Sigh. > > > And I've got to figure what to do Monday as my lady adds another > > > year to her journey on this ball of rock and water, making it to > > > her 79nth. > > > > > > Something she'll appreciate without any physical effort. With > > > copd, there's not much of that left. Sigh... > > > > > > That said, I think the DC method can be made to work with a > > > separately wired probe, with both the ground on the workpiece and > > > the hot on the probe wired independently from the machine. Run the > > > probe cable as a shielded wire in the cable chain. At least this > > > chain can be opened to add more wire, something none of the other > > > cable chain I've bought can do. Nice! > > > > > > > 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 > > > > <ghesk...@shentel.net> > > > > > > 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 > > > > > Emc-users@lists.sourceforge.net > > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > Cheers, Gene Heskett > > > > 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 > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
