Ball screws can be had that long, but they aren't cheap and you're in rotating nut only territory.
I've bought custom length screws directly from Hiwin for reasonable amounts of money (a C7 rolled screw and nut cost about half what the machine's OE charges for a replacement lead screw and so far it has lasted more than 3x as long.) https://motioncontrolsystems.hiwin.com/configurator/ballscrews-main-configurator Todd Zuercher P. Graham Dunn Inc. 630 Henry Street Dalton, Ohio 44618 Phone: (330)828-2105ext. 2031 -----Original Message----- From: Roland Jollivet <roland.jolli...@gmail.com> Sent: Thursday, October 04, 2018 3:46 PM To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net> Subject: [Emc-users] Yet another topic about gantry homing The OP said the table is 3.8m long.... On Thu, 4 Oct 2018 at 21:35, Chris Albertson <albertson.ch...@gmail.com> 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 > > > > > -- > > Chris Albertson > Redondo Beach, California > > _______________________________________________ > 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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
