On Thursday 18 August 2016 10:14:53 Todd Zuercher wrote: > I have a machine that I converted from step-motors to servos, and I'm > having a little trouble with the Z axis. It has an anti backlash lead > screw with a 5tpi screw. This sort of worked, but the servo was > working hard to move the head, and I wanted a little higher encoder > resolution for better tuning. So I swapped in a nearly identical 10tpi > lead screw set I happened to have on hand (removed from another > stepper machine to get better speed and perfomance). I thought that > the 10tpi screw should be easier for the servo to turn, but I'm > finding that the opposite is true and the servo can't raise the motor > without counter balance assistance when it could with the 5tpi. Does > that make sense, or is the problem more likely that the 10tpi screw > and nut are worn out and binding?
Need moe info. If the 5tpi screw was a ball screw, and the 10 tpi was acme with a bronze nut or two so backlash can be taken up, then the 10 tpi is likely at least twice as hard, possible 4 or 5 times harder to turn under load. Because of that, my toy HF mill has a parallel wired 425oz motor on top of the totally rebuilt Z drive. Its actually faster than the 262oz turning little ball screws for table motion but I do keep it well lubricated with a grease fitting feeding the space between the nuts. I need more motor voltage as its only 28 volts. I have the 42 volt cure for that, but haven't found a round tuit as I want to put a 5i25 in it at the same time. Too busy working toward the Sheldon being cnc'd ATM. If both are ball screws, then I am puzzled. There really is not a good substitute for ball screws and nuts. So in my machines, that z drive on the toy mill, is the only non-ball screw. With doubled bronze nuts, its quite easy to maintain sub 2 thou backlash and 1 thou can be had right after a re-adjustment of the top nut. But nooks prices for those haven't come out of the stratosphere, I have about $175 in that screw and two nuts, when ball screws from China can now be had in C7 grade for half that. And if backlash in the ball nut creeps in, I've found you can buy oversized balls in 500 count bags on fleabay. Getting the return plugs out in a Chinese nut seems to be a problem so the best is to unscrew the nut & let those balls fall out, then rig it vertical so you can feed the bigger balls into the end of the nut and walk them into the grove, screwing the screw back into the nut as you fill the groves. In a nut with return tubes you can remove, its a bunch easier to get the nut filled up and put the tube back on and walk the last 7 or nine balls to fill the tube into it. BTDT, several times now. 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
