On Friday 05 October 2018 23:24:38 Chris Albertson wrote: > A third option is a REALLY long belt. It is long enough to make a > double pass on each side and needs about 8 pulleys but you only need > one motor. I saw one of these once but it used a kevlar cable, not a > belt > > I think the shaft is move simple but but you need precision mechanics > to adjust it. It is ever comes apart for service you'd need some good > measuring tools to align it. But with two motors the adjustment > misdone in software and the mechanic doing the service only needs to > get it "close" by eyeball with a tape measure. find adjustment is > later in software. > > My dirt cheap 3D printer uses two motors and parallel screws and I use > basically a sheet of paper as a feeler gauge and I can reset alignment > in abut 30 seconds to about 0.005 mm. > > Any design can work as long as you have a designed on squaring method > that can be done with simple/cheap tools > > All the talk about the long axis but I think the REALLY hard part is > the Z axis. Lets say you make a cut that is 0.15 mm deep and 3 meters > long. Will it remain exactly 0.15mm deep over that long distance? I > bet you a buck not. > No takers on that bet Chris.
If indeed its that critical, one would need a dynamic distance detection method of some sort riding the work pretty close to the tool, which would be outputting the instant offset, and would be driving the Z to maintain that distance in real time. And the success of that would be in building it to not be material sensitive, or subject to getting tangled with the cuttings. Because it has to operate in a pretty noisy environment, I'd design it with a hardened ball pointed lever, sitting the ball quite close to the tool, and pivoting a couple inches away from the cutter, with the far end moving a ferrite slug in and out of a coil which was part of an oscillator running at 100+ kilohertz, and some sort of a frequency discriminator, possibly a crystal referenced phase locked loop, using the pll's error as the signal into an offset module. With the correct gain, I'd say you could make a working correction circuit that would reduce a 5mm error to +- .01mm, which might be close enough. That wouldn't care how long or wide the bed and workpiece are but the lever should be constrained from dropping over the edge of the workpiece and being caught and destroyed. That implies a bigger ball. The ferrite slug could be moved by a small wire thru a hole in the shielding so other electrical noises wouldn't bither it too much, or were fast enough that the drive motor will function as a noise integrator. This could be centered in the control range by useing a screw the pivot point up and down with a hand knob, on the levers pivot point height. With the tool stopped, adjust the slider with the rest of the circuit live, so the tool touches the work or holds a paper slip, then dial an offset in with a sum2 to drive the tool to the desired depth. And apply just enough shop air to keep the contact area 99% clean. Theres probably a few more ways to skin that cat, as all of this would have to be moved with the z drive, but thats what I'd try since the electronics are fairly well understood here at the coyote.den. Making the hardware would take me some longer than some of you. But I'd get it done as long as I'm still looking at the green side of the grass. ;-) Not having the real estate for a big gantry machine would slow me down I expect. -- 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
