Speaking of backlash. My tiered old Bridgeport has about 0.002" of backlash in the ballscrews. So if circular interpolation is used there is a small bump at each 90 degrees of the circle. But if I make the finish pass first clockwise and then repeat counter clockwise the imperfections are much smaller. I know from experience with my first CNC machine that's built that actually used leadscrews with lots of backlash the clockwise followed by counter clockwise method was remarkable compared to a single direction final pass.
John On Tue, Aug 3, 2021, 10:10 AM jrmitchellj <[email protected]> wrote: > You might try the run again without the backlash compensation in LCNC to > get a feel of what it is actually doing. > > > --J. Ray Mitchell Jr. > > > “I predict future happiness for Americans, if they can prevent the > government from wasting the labors of the people under the pretense of > taking care of them.” > > THOMAS JEFFERSON > > > On Tue, Aug 3, 2021 at 6:24 AM Gene Heskett <[email protected]> wrote: > > > On Tuesday 03 August 2021 05:31:56 andy pugh wrote: > > > > > On Tue, 3 Aug 2021 at 07:58, <[email protected]> > > wrote: > > > > I draw all this from my own ballscrew conversion of my own mill, > > > > some 20 years ago. If I was doing it again, I would use two nuts, > > > > with spring tension between the pair > > > > > > Springs might not be the best way. The common way to tension double > > > nuts is to (basically) screw them into each other and lock the angular > > > relationship. > > > > > > You _can_ get preloaded single nuts, using oversized balls. That only > > > works if the ball track is the right shape, though, it needs to be a > > > 4-point contact shape. > > > > Which I'd suspect as being subject to rapid initial wear until it was > > just a normal screw with about a thou of backlash. > > > > For me, I bought C7 grade which may have 2 thou but in several years has > > not gotten significantly worse. Protecting the screw from contaminants > > is the most important thing for long life. On my Sheldon, the Z screw, a > > 1450mm long 25mm C7, got sealed bearings on both ends, a collar to clamp > > a bellows to on both ends of both sections, and 2 of the 6 mounting > > holes in the nut were drilled all the way thru so air could get from one > > side of the nut to the other as the nut moved. The nut gets one pump of > > grease a year. Backlash, some of which is in the end bearing, was about > > 1.9 thou 5 years ago and still is. It has not been uncovered in that > > time. I don't have a bellows on the x screw but its channel in the > > carriage is sealed top and bottom unless the carriage is clear in. > > exposing the screw behind the QCTP boss. No compound since LCNC is > > better than mechanical you set by eyeball. Plus it was busted from a > > fallover when I bought it. I keep a rag over the slot in that event. > > > > That faint thumping? Me, knocking on wood, no swarf has gotting into it > > yet... > > > > 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) > > If we desire respect for the law, we must first make the law respectable. > > - Louis D. Brandeis > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
