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
