On Sunday 20 May 2018 18:37:54 Frank Tkalcevic wrote: > > I paid abut $30 for a very good 16mm diameter by > > 500mm long zero backlash ball screw and nut. Yes truly "zero" > > there seem to be two ball nuts working in opposition. If there is > > backlash on the > > $30 > > > screw it is less them by dial indicator can show. > > Where did you find these? Most ballscrews on ebay are called > "zero-backlash", but don't have opposed nuts. > And in my experience, need shimming in the thrust bearing assembly as the majority of the backlash, even in single nut styles, have 2 to 4x the backlash in the thrust bearing than in the nuts. I could take up another 4 thou in the big 1450mm long screw moveing the carriage on the sheldon with a little more shimming between the inner races of its AC bearings right now. OTOH, I have less than $200 in that 25mm diameter screw.
I didn't get thrust bearings with the teeny screws I bought 3 of from PMDX. black finished, salvaged out of something, nuts had no mounting provisions so I had to make cages to contain them, but they were small enough to fit in the X1 mill which is very crowded. 8mm maybe. But I was able to source a bag of .001" (.0635 average) oversized balls on ebay, and restuffed the nuts, so with shop made thrust washers and the oversized balls, backlash on that toy mill has been under 2 thou, but the felt washers I put in for ball lubeing(I also rigged a lube manifold to feed vactra to them) and swarf wiping have since collapsed, so I've had to tighten the nut endplay adjustment once and it could use it again as its above 3 thou again. I have never found a similar sized screw for sale on ebay. While g76 threading on the Sheldon yesterday, I found I am going to need a tapered gib on the rear of the carriage, the cutting forces were lifting it and rattling the wrench laying on the rear of the crossfeed cover. Like Gilda was fond of saying, its always something. I think I've seen similar goings on on the front of the carriage too, evidence of a cant of the carriage as its lifted on the v-way, it cuts about 2 thou smaller in one direction, so if and when I find that famous round tuit, I may as well make both. Both front and rear now have full width heavy brass gibs, but bed wear etc over 70 years gives it some wiggle room. Sigh. > ---------------------------------------------------------------------- >-------- Check out the vibrant tech community on one of the world's > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users -- 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
