On Tuesday, March 06, 2012 08:29:24 AM Tony Zampini did opine: > Hi everybody, > > I just made my first PC board using EMC2 and my Sherline mill. > I was surprised at how nice it came out. > > One issue came up, however, during the drilling phase. When EMC2 > paused for the tool changes, I didn't see a way to touch off the Z axis > after installing a new drill bit. Is there a way to use "touch off" > while the tool change dialog box is being displayed? > > Thanks, > Tony
I went at that from a different angle Tony. I made a micarta pallet to hold the pcb so that it was insulated, with the pcb pocket milled about 30 thou deep, and in two steps so there was a ledge about 40 thou wide around the edge that the board sat on, but had another 10 thou or so clearance under the middle of the board, and the edges of the board filed so that it had a very close fit, no sideways wiggle room. A 4-40 screw in each corner held the board. Then I set a 3/8" long piece of 1/8" brass tubing from the model makers shop, into the micarta about .2" to the left of the left front corner, with a short wire soldered to it so it could be trapped under a small piece of metal, connecting it and the tubing to a wire from the parport pin 17, which all serves as the contact for a G38.2 probing operation. For an initial probe to calibrate the G55 and G56 offsets which are used to mill the top G55, and bottom G56 sets of co-ordinates, I made a probe from a sewing needle threader by mounting that teeny bit of spring in a 1/8" brass tube, put that in the same 1/8 collet in my spindle. Since that would be very difficult to bend to get dead straight, I bent it so that the folded tip of this fine wire can be seen to have an arrow pointed profile when the spindle is running at about 600 rpm. I added a 2.2 uf tantalum capacitor across the probe cable that would be discharged to hold the logic zero long enough to be detected reliably. The mill is positioned such that this probe wire is sitting roughly in the center of the end of that brass tube, and tholefinder.ngc, a small utility I wrote is run. When it has finished detecting the exact center of the tubing's bore, rehome the X & Y axis's of the mill in G54 co-ordinates. This code has set the G55 and G56 co-ordinates so that both sides of the board will be in registration. This code will need adjusted some to match where you put the tubing into your pcb holding pallet. Get it at the site in my sig, scrolling down to the word 'here' that is a link to "Genes-os9-stf" where you will find a subdir called "eagle", get 3 files from there: tholefinder.ngc tedautoz.ngc bedautoz.ngc. To use the autoz functions, edit them to use a spot on the board that doesn't have any parts and has solid copper connected to the connection you have clipped the probe cable to. I used a spot .2" right of the left edge of the board and .1" in from the front edge, not very far from the left front hold down screw. In the output files from pcb2gcode, edit those, adding a "call tedautoz" as the next statement line after any M06 T# lines, so that it is executed as the next thing after you have clicked ok on the tool change request. Do this to all the *.top.* files, and similarly, add a "call bedautoz" in all the *.bot.* files after each M06 T# call. I store that wire probe in a piece of 5/32" tubing when not in use to protect it from getting bent after it has been "adjusted". It also has a small length of this tubing soldered over the 1/8" tubing to serve as a depth stop when inserting it into the 1/8" collet in my micromill, your sherline might have a different arrangement of course, but the principle is the same. The pcb's I have made have not been marked enough by the probing operations that you can tell where the probes touched. These code routines also assume that you have spindle on-off-speed control from LinuxCNC, which I do. Each of the autoz files also has an adjustable fudge that you can adjust to control the depth of the engraving bits cut, the ideal target being just deep enough to go all the way thru the copper but no more. You'll want an air nozzle directed at the tip of the bit to sweep away the debris, I use the smallest brass tubing for that, with a pressure regulator set for perhaps 20 psi so the compressor isn't running very often. Attached to the mills head so it follows the bit. If you cut too deep of course, and you are using glass board, then you will have very small glass fibers in the air. This isn't exactly healthy for lungs, similar to asbestos in the long term effects on the lungs. I adjust that "fudge" parameter in the autoz files until I can't see copper left at the bottom of the cut line, usually in .0005" increments. Properly fine tuned, I can make a decent board. The rest of the files in that 'eagle' directory are the files I used for the spindle encoder I have installed on my POJ 7x12 "Speedway" lathe. That is a work in progress and will have more pix of the project added as I take them. I call it a POJ for good reason, everything I have taken apart has required additional machining to correct factory defects and make it run smooth. The carriage cross slider was no exception, even the bolt wasn't running level with the slides motion! The gib strip was bent, about 3/8" in the middle, and 50 thou fat on one end, holding that corner of the slide up like it was on a spring. Lots of draw filing to fix that. I might have a usable lathe eventually... Have fun! Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> Old musicians never die, they just decompose. ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! 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