Perhaps victims of the Trump tariffs! --J. Ray Mitchell Jr. [email protected]
"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 <[email protected]> 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. > > > > > > > > > > > > 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 <[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 > > > > 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 > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
