On Friday 13 September 2013 22:11:07 Cecil Thomas did opine: > Andy, > That solution has occurred to me and it might be the way I'll go. I > have the stepper and the gecko to drive for it and room in the > control box. The speed knob is connected to the rheostats by a chain > drive (similar to bicycle chain and sprockets) I can just put a > sprocket on the stepper and engage it into the chain at a convenient > location. > > I can even hide it inside the machine so no one will know it's > there. Also there will be no impact on full manual operation. I'll > have to do a little dance with variables to convert an "S" value into > equivalent rotary or linear motion so the stepper won't know what > it's really doing. > > The default lathe setup has only 2 axes. It is not obvious to me how > to add the third axis for the speed knob. Can I add the third axis > in the .ini file without messing up anything???? > That I think depends on what you want to do with your lathe. Most will have sufficient room on the back side of the spindle to allow an encoder disk (there are lots of patterns to carve those for the grabbing out on the net) to be mounted and read by opto interrupters, which in turn tell linuxcnc where in the rotation cycle and which direction the spindle is turning. So in your case you could use a stepgen(erator) module to drive the controlling stepper so as to drive the stepper to the desired speed. This same circuitry can also be used to 'servo' the speed, as if you are 2cm from the start end of a thread you are cutting, and the spindle will respond to the cutting load by slowing a bit, but you'll see the rheostat moving to effect a correction quite quickly.
This is sufficient to allow you to cut threads of any size and pitch with no gears mounted in the headstock, using the canned gcode cycle G76. The coupling of the carriage movement to the spindles rotation is at least as tight as the old handful of change gears methods. Threads are downright purty if the tooth is sharp. Now, the control you are describing can, just as easy as adding a relay under gcode control (M3-M4) to reverse the motors field polarity, be made into a reversible spindle, all under gcode control. At that point, you can also consider rigid tapping using the G33.1 canned cycle because that same electronic gearing is active for the carriage motion in both directions with a small free period as the carriage moves to the right of the starting point. Taking pity on my teeny little taps (I go down to 0-80's), I wrote a peck drill wrapper that adds a half a turn to the depth until the depth has been achieved. I haven't broken a tap yet, but you can probably hear that faint thumping sound of me, knocking on wood. ;-) The .hal file gets fairly complex to do all that. I am doing all that on my tricked 7x12 FWIW, with one remaining bug in my .hal file, I noted about a month ago that I can't start the spindle in reverse, but can start it, then reverse it before its turned more than a couple degrees. That was one condition that my G33.1 function checks didn't catch. :) My .hal file is 265 lines long, but I doubt that is the largest .hal file in /this/ crowd. > Andy Pugh said > > >It's a very Heath Robinson[1] solution, but a small stepper motor > > moving the rheostats would work and would not risk breaking anything. > > Thanks again, > Cecil > ------------------------------------------------------------------------ > ------ How ServiceNow helps IT people transform IT departments: > 1. Consolidate legacy IT systems to a single system of record for IT > 2. Standardize and globalize service processes across IT > 3. Implement zero-touch automation to replace manual, redundant tasks > http://pubads.g.doubleclick.net/gampad/clk?id=51271111&iu=/4140/ostg.clk > trk _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users 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://gene.homelinux.net:6309/gene> should be up! "Oh my! An `inflammatory attitude' in alt.flame? Never heard of such a thing..." -- Allen Gwinn, [email protected] A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ How ServiceNow helps IT people transform IT departments: 1. Consolidate legacy IT systems to a single system of record for IT 2. Standardize and globalize service processes across IT 3. Implement zero-touch automation to replace manual, redundant tasks http://pubads.g.doubleclick.net/gampad/clk?id=51271111&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
