On 01/22/2014 05:58 PM, Jeshua Lacock wrote: > > > Hmmm, what machine are you referring to? I just checked and I have full > 8x12x3 inches of travel for the mill. Well, yours seems to have the adjustable head height, ours doesn't. It also sounds like yours may be overall a larger machine that ours. > I have been using it to lathe hardened steel shafts and has been turning like > a dream so far. Haven't yet milled anything though. Yes, it seemed it made a better lathe than a mill for us, too. But, since I have a Bridgeport mill and now a 3500 Lb. Sheldon lathe, maybe I'm just prejudiced. > I figured backlash was common to just about all reasonably priced mills, and > I was wondering what folks did with them to compensate with CNC. The X and Y on my 150 Lb minimill was surprisingly low. See http://pico-systems.com/minimill.html I usually only use it at shows to demo my CNC hardware and LinuxCNC, so it is lightly used, but backlash is still just a couple thousandths of an inch. > I just checked the backlash on my Z and with the micro-adjust knob I can > not feel any discernible backlash. I certainly can feel backlash on the Z > quick feed and on the X and Y leadscrews. Well, that's where the backlash is, so twiddling the fine feed knob is misleading you. What you need to do is put a dial test indicator on the quill and push up and down and see how much the indicator moves. > Eventually I would like to replace them with anti-backlash ballscrews. I > would like to get the machine up and running first if I can expect reasonable > results from it. I think I read somewhere a while back someone compensated > for the backlash in software and virtually eliminated the problem without > having to replace the leadscrews. No, that is a fantasy. For X-Y positioning work, ONLY, you can sort of eliminate backlash, but the fact is the screws don't constrain the table, so cutting forces can move it over the range of the backlash. Even without cutting forces, the motors would have to move at infinite speed to get from one side of the backlash to the other to create correct motion. So, in my opinion, backlash compensation is a fantasy that doesn't work in actual practice. > Speaking of anti-backlash ballscrews, have you guys seen this printable: > > http://www.thingiverse.com/thing:125529 Threadless? Then, what gives you predictable movement? Nothing, I gather. So, you can move left or right, but without a measuring device on the table, you have no idea how much it has moved. > > > Yeah I was planning on going with Gecko. Good to know, thanks Jon! > > I guess the biggest uncertainty right now is how much torque I might need on > a machine like this. I was guessing something like the first stepper listed > here: > > http://www.kelinginc.net/NEMA23Motor.html > > > 570 Oz-In is a lot, but of course, that is only at standstill. But, they should do fine, especially with a belt reduction. 5 A will require the "big" Gecko 203 drive. For that, you might consider Gecko's servo motors and our PWM servo drives. The price would be pretty close, and the performance will be a lot better. I can advise on specific models, encoders, etc.
Jon ------------------------------------------------------------------------------ CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments & Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
