On Wednesday 28 October 2020 05:22:12 Roland Jollivet wrote: > Hi All > > I'm wondering about probing, maybe someone can shed light; > > I want to make a touch probe, and looking at the classic Renishaw > tripod style, an obvious limitation is the lobing error. > Is this appreciable (<5um?) or is it dwarfed by taper-mounting and > spindle error? > > So I'm wondering why M19 Pxx isn't used, to always turn the probe > towards the most sensitive direction? Or is it? This could also > negate any spindle related error when touching off on opposite sides. > > Alternatively, I could also make a very sensitive one-direction-probe > and always use M19 Pxx when touching off, much as one does with a > lever dial indicator. > (and have a separate Z probe) > > Roland > > PS, I don't have a M19-able spindle or probe yet, so I might be off in > my assessment..
A technique I've been using for years is a copper wire, about 10 ga from a piece of romex, mounted in a 3/4" dia piece of teflon stuck in an r8 collect of that size. I use it to find the center of a hole in order to make that the reference zero for the rest the currently loaded program. To remove any error caused by the bending of the wire, I do three things. 1. I put a .1uf cap to ground on the wire wrapped around the probe wire so it will be discharged by a momentary contact and held at a logic zero long enough for lcnc to detect it. 2. I run the spindle at 2 to 4 hundred revs, usually in reverse so the probe wire describes a circle as perfect as the spindle bearings are. 3. I probe each holes quadrant twice, once rapidly to find the wall of the hole, back off 10 to 20 thou and repeat the contact search at much lower speeds. This is done once each 90 degrees. the second contact is recorded in each case. Then the machine in moved to the mathematical center of the 2 directions x & y and left there where I can touch off both axises. And I usually repeat to see if its accurate enough. By this method, I can locate the hole, repeatedly to an error of a couple tenths of a thou. I've used it to make double sided circuit boards where each hole was only drilled about 40 thou into the board, turned the board over in the pallet, and then drilled from the other side and the holes meet in the middle of the board thickness with no detectable offset. I do tlo measurements directly from the tool, by mounting a piece of pcb, copper up, someplace on the table, or top of a jig, as long as you know where it is, and connecting the probe wire to the copper, lower the tool, turning backwards until contact, the reverse doesn't cut, or even mark the copper, but your g32.8 data is the tlo you can apply in your gcode. Watch for signs of z sled stiction and re-oil the post with vactra-68 if needed. This, if the sled is moving smoothly, can be accurate to a tenth of a thou. Similar results in metric. I do have dials, but this uses the workpiece, dials not needed. For precise work in wood, I use a half of a brass cube someplace on the jig locating the wood, and probe the two sides and bottom with the cutting tool, turning backwards of course. And write the code to comp for tool radius. I've found when cutting green and green style box joints, that a slight reduction in tool rad will result in a joint that fits perfectly dry and needs a minimal amount of Elmers or Titebond for a truly excellent glue joint with no squeezeout to clean up. Elmers preferred because of its longer setup time when driving all the screws in a 1x12 end joint. Thats how I do it. But I've never claimed to be a trained machinist. I am a C.E.T. and this is all intended to keep me out of the bars in my dotage. 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
