On Friday 08 September 2017 14:41:37 andy pugh wrote: > On 8 September 2017 at 19:19, Gene Heskett <[email protected]> wrote: > > Since I've no clue what the tpi or tpmm is on that nominally 8mm > > screw driving the X carriage > > Is this a ballscrew or the original feed screw? > Small ball screw. Backlash, currently well corrected, is .0021".
> If it is the original screw then it might be worn. > OEM screw and nut both well toasted. Nut had been repaired with a helicoil once, and was quite near stripped a second time. The taper attachment was removed, and a new shaft fitted with roller thrust washers now anchored on the front and rear faces of the original crankshaft bushing screwed into the front face of the saddle. Its turning in needle bearings and the X motor is driving that new shaft. This is what the tapered rear of that newly made shaft I was taking about is using to grab the end of the screw and drive it. The taper and matching tapered nut has a several ton per square inch grip on the screw, which is also coated with green threadlocker. The ball nut, which has no flanges or threads on it, is in a cage I made and has no play as its driven against the inside face of the cage with some 3mm screws. The only give in that is the heavy felt washers compressed against both ends of the nut by those screws. The whole thing has a sealed with goop opening in the bottom, and the bolt hole in the top that attaches it to the crossfeed slider, and I also sealed up the bottom of the saddle below the screw, and the slot in the top of the carriage. The rear of the saddle is sealed about 20 thou past the end of the screw, so the only swarf entry point is the bolt access slot in the top of the saddle if I am working at small diameters, but if I note its uncovered, I'll stop and move the QCTP inward on the crossfeed enough to push it back and cover it up again. I can also rotate the block of iron that fills up where the bent and broken compound feed was, so I have over 4" of adjustment in the toolholders position available. Usually mounted such that the tool tip is within the cross slides footprint on the saddle so there shouldn't be any tipping forces to lift one side or the end against its ways. > Setting up the linear scale and making a screw-mapping file might > help. Thats true. One has to assume the linear scale is sufficiently accurate to correct the screw. But is it? A $40 Chinese scale that I believe has a data port, possibly even be powered from an otg usb port. Its display is remoteable by 2 or 3 feet of cable. Which then makes me ask, do we have a module that could talk to it? Its not in the 7i90 firmware in any version, strictly a bit at a time unless an encoder module in the firmware could be highjacked, a unk bit of trivia. And would be the last one in the current configuration. All big if's. So it handling the data from a local usb port, it may be subject to the same missed events the local keyboard and mouse are subject to on the pi-3b. I'll see if I can rig it from the saddle to the crossfeed in the next days & see if it calls my dial a liar. And advise what I found of coarse. Rock64's, 2nd shipment should have shipped the 6th. But I haven't made the trek to the mailbox yet today. :( Thanks Andy. 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
