Would a better solution ( or an as_well_as solution) be to have two saddles spaced widely apart? Or maybe we should all just save up and buy a Tormach. Slant-bed doesn't solve the basic problem, but its a good way to go.
Marcus On 29 Sep 2014, at 03:35, Gene Heskett wrote: > On Sunday 28 September 2014 21:54:25 andy pugh did opine > And Gene did reply: >> My lathe is rubbish. That's just a fact. Luckily the lathe is a rather >> clever mechanism and even a bad one can make decent parts due to >> fundamental precepts of geometry. >> >> What I noticed today was that the saddle can twist. I think I have the >> rear gibb a bit tight for anywhere more than 5" from the chuck. The >> fact that there is a gibb is my own upgrade, the OE arrangement was >> some cast iron plates with screws that were not quite tight onto a >> painted surface (did I mention that my lathe is rubbish?) >> >> So, I started thinking, and it occurred to me that whilst the >> traditional lathe solution to the fact that the leadscrew is offset >> from the point of action of the tool is to have a saddle with long >> wings, you could have a short saddle that only controls in X with dual >> ballscrews to keep X perpendicular to Z. >> >> I _think_ that this makes some things easier, as you can have a short >> saddle which makes missing the head easier, and leaves more room for >> the screw covers. And, you can adjust the X-Y squareness, which is >> normally impossible. >> >> Apart from the extra cost, what is the drawback? > > The requirement for a totally backlashless coupling between the screws? > > I too have a similar problem with my toy 7x12. And because the gibs are a > cast iron bitch to adjust, I've considered pulling the no longer used > rack, and adding an at least as long as the H wings bar front and back and > putting small ball bearings on some sort of adjusters to ride the bottom > of the front lip and back lip, which should reduce the friction from > trying to keep the gibs tight enough. Its slightly compounded on this > early 7x12 as the angle faces on the front of the way, and the angle cut > in the saddle didn't match by several degrees. With a front gib pulled up > tight, and the rear one off, the back of the H is lifted, originally about > 3/16", now maybe 5 thou. > > I milled that out to a better fit and its wearing in nicely over the last > 5 years, nearly stabilized. But with a QC toolpost, the offset from the > hold down bolt causes the tool to overhang the front of the H and heavy > cuts lift the right of it a thou or 2. > > OTOH that does seem like an awful lot of work as I'd still have a sows ear > lathe. > > Bolton has an 11x28 (23 between centers) with a variable speed motor that > sells bare for about $3000 USD. The B290VF. Marked down some now. $2721 > w/6" 4 jaw & backplate. What can this group say about it? Good or bad? > > Is it worth putting ball screws in it? > >> This isn't the same as a central leadscrew, by the way, that's nice, >> but in that scenario too, the scew can't keep the saddle square. > > > 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> > US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS > > ------------------------------------------------------------------------------ > Slashdot TV. Videos for Nerds. Stuff that Matters. > http://pubads.g.doubleclick.net/gampad/clk?id=160591471&iu=/4140/ostg.clktrk > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Slashdot TV. Videos for Nerds. Stuff that Matters. http://pubads.g.doubleclick.net/gampad/clk?id=160591471&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
