They are on ebay. Yousearch for "ball screw" and they come up. Here is an example: https://www.ebay.com/itm/SFU1204-RM-Rolled-Ball-Screw <https://www.ebay.com/itm/SFU1204-RM-Rolled-Ball-Screw-C7-w-1204-Flange-Single-Ball-Nut-End-Machined-CNC/182984364227?hash=item2a9ab7d0c3:m:mRPMtPkRsQJgkW_GJutMw2Q&var=690294923392> Here is another: ebay.com/itm/CNC-SFU1605-Ball-Screw <https://www.ebay.com/itm/CNC-SFU1605-Ball-Screw-SET-L300-2000mm-Ballnut-Housing-Coupler-BK-BF12-US/352275520560?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D52885%26meid%3D42d4afe676a5420b9da6da9c19401ec2%26pid%3D100005%26rk%3D5%26rkt%3D12%26sd%3D182984364227%26itm%3D352275520560&_trksid=p2047675.c100005.m1851>
Notice the number "1204" this means 12mm diameter by 4mm pitch. the other common size is 1605. You can look up there specs on Google by searching for SFU1204 specification and find the data. When you do yo find that even a 12mm screw has some inside strength like 1,000 pounds or soothing but that does not matter the real limit is how fast you can spin the screw before it "whips". Yo can NEVER remove the nut. So design accordingly. the other thing is that the balls are held in compression. there is a spring inside the nut so there is rolling resistance because the balls are under load. This is good because it removes backlash but I bet you'd see balls shooting all over the shop if the nut came off the end. The 1204 size is nice because with a normal 400 step motor it you run half steps the each is exactly 0.005mm and that is good enough for a milling machine. (works out to two 10ths in US units) One more "got-ya" the two "flats" on either side of the nut are not flat it is a taper. It is good they did this but I did not notice at first. On Fri, Oct 5, 2018 at 8:11 AM Dave Cole <linuxcncro...@gmail.com> wrote: > Chris, > > Do you have a link for these "new style ball screws" ?? > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
