On Friday 05 October 2018 11:12:01 Dave Cole wrote: > Chris, > > Do you have a link for these "new style ball screws" ??
Just do a google search. The prices seem to be in freefall. The 1 start, 25x5x1450mm screw and nut, with bearings I paid right close to $180 usd + ship, about $200, for the Z drive on my 11" sheldon, can now be had for about $80 USD with free shipping. Smaller, & shorter screws are down to beer money, still with free shipping. I'm amazed. And I'd nearly bet the thrust bearings are tight to start with instead of 10 thou of sloppy backlash/endplay in what I bought. I finally did find a round tuit and added 10 thou of shims between the outer races of the AC bearings, a bit much, but I just brought the nut up to a wee bit of preload and locked the screw. Z lash is now around 1.1 thou. > Thanks, Dave > > On 10/4/2018 3:33 PM, Chris Albertson wrote: > > Have you seen the new style ball screws? They are now cheaper then > > belts and have pretty "over kill" specs. > > > > The problem with a 30mm wide belt drive is the need to resist the > > belt tension and a way to adjust it. Not only the tension between > > the two pulleys but there is side load on the motor shaft unless you > > use a flexible coupler and ball bearings on both sides of the drive > > pulley. The lead screw is mechanically simpler because the > > motor can be directly coupled to the screw and for $70 you get all > > the end blocks and mounting hardware. These have made router design > > nearly a "screw driver only" project. No design to even much > > thinking needed. I bought one for the vertical axis of a CNC > > milling machine and I can set there is zero backlash and not adjust > > needed or the life of the machine. Cost me about $35. > > > > A screw give the drive motor a larger mechanical deduction and you > > can likely skip the need for a reduction stage. A screw might > > advance the axis 4mm per revolution but a belt drive moves maybe 30 > > to 36mm per rev. You get more force the resolution with a 4mm pitch > > ball screw. > > > > You can make a one meter square X,Y router base or laser cutter > > today using two pair of supported rails and two screws for under > > $250 plus the motors and your z-axis. > > > > On Thu, Oct 4, 2018 at 11:41 AM Roland Jollivet > > <roland.jolli...@gmail.com> > > > > wrote: > >> The idea of using belts, and gearboxes, and rack and pinions, > >> sounds like a bad recipe. > >> > >> While I did suggest a bar across the gantry, the problem is that > >> you're carrying all those gears, and the motor. > >> I drew a quick concept sketch of how I would do it. Buy > >> cut-to-length belt, probably HTD M5 x 30mm wide for your > >> application. > >> > >> I think this would be quite adequate for a wood router. At the far > >> end of the table, connect the two idler pulleys with a shaft too. > >> Obviously all the pulleys and motors will be below the table > >> height. > >> > >> And; > >> - motor is no longer on the gantry > >> - no skew can happen > >> - easy to get your drive ratio > >> - single motor > >> > >> http://imgbox.com/ccZJF5nH > >> > >> > >> > >> On Thu, 4 Oct 2018 at 17:41, Leonardo Marsaglia > >> <ldmarsag...@gmail.com> > >> > >> wrote: > >>> Hello Les, > >>> > >>> No, I plan to support 50 mm bars every 600 mm more or less. I'm > >>> attaching some pictures of the design I'm working on. (The > >>> adjustable stands for levelling are not in the assembly because > >>> I'm saving resources on this laptop) > >>> > >>> I like the idea of using the rectangular ways but unfortunately > >>> they are quite expensive for this project and also there's the > >>> aligning problem. With the setup I'm trying to do I can adjust the > >>> parallelism on every corner of the machine and also individually > >>> adjust every suport to level the guides perfectly. I'm sending > >>> pictures of everything to clarify what I'm intending to do. Please > >>> note this is under development and some > >> > >> things > >> > >>> are going to change a little bit. > >>> > >>> The idea of welding the frame is out of discussion because I plan > >>> to move and set up this thing in place. Also, I don't have the > >>> means to > >> > >> guarantee a > >> > >>> clean and squared welding for the frame. Instead I decided to do > >>> what you can see in the pictures, having an enormous amount of > >>> bolts to keep the parts rigid and firm. > >>> > >>> No problem about using tubing to lower the inertia. I also thought > >>> about reducing the 3000 max RPM with the worm and gear to 100 RPM > >>> on the shaft and then increase the size of the pinions to have the > >>> linear speed I > >> > >> want. > >> > >>> This way the long shaft doesn't have to withstand the high RPMs. > >>> > >>> I uploaded the pictures because the list doesn't allow me to > >>> attach them. Here's the link: > >>> > >>> https://imgur.com/a/7kLUWsq > >> > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > 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. 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