You're describing a VERY weak, overly complicated system. Even small machines get pretty sloppy with that sort of linkage. Cross shafts have a ton of inertia and a lot less torsional stiffness than people think. Belt drives have been pretty springy on even the tiny Shapeoko stuff, and it causes a lot of cutting distortion unless you're running it dead slow.
R&P drives work exceedingly well. The only way you'd ever link them would be a torsion axle all the way down the gantry and sub-belts down to the R&Ps- and the correctly done R&Ps do rotate and have their own tensioners. So mechanically complicated and not a mechanically stiff solution either. Danny On 3/31/2016 7:36 PM, Gregg Eshelman wrote: > For convenience and especially for operation by students, newbies and the > generally clueless, build or modify the gantry so both sides are mechanically > linked so it is Not Possible for it to get out of square. > If you have a screw running lengthwise on both sides, Put a chain or belt and > idler across one end and on the other, use a center shaft with three stacked > sprockets so there's a chain to each screw and the third has its own belt or > chain to the motor. > Another method uses racks along the sides and a shaft across with gears on > each end. A variation on that is with a length of roller chain fixed at the > ends then wrapped around sprockets and idlers in the vertical ends of the > gantry, with a cross shaft to drive like with the racks. > Then there's the 'wraparound' gantry with a beam that crosses under the table > with a single drive down the center. The weakness there is the gantry can > still rack a bit freely if the bearing parts are any bit loose or aren't long > enough to stay self aligning. The design also needs a very stiff and strong > table structure due to the impossibility of having any supports except at the > ends. > > Why does anyone want a gantry that's has the built in ability to try and rack > and jam up when it's simple to build one where that isn't possible? > > It simplifies the software and the electronics, eliminating one motor and > driver and the need to home each side of the gantry and tweak the software to > keep it straight. > > > > > From: "dan...@austin.rr.com" <dan...@austin.rr.com> > To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net> > Cc: Dewey Garrett <dgarr...@panix.com> > Sent: Thursday, March 31, 2016 10:13 AM > Subject: Re: [Emc-users] XHC-HB04 on LinuxCNC > > But wouldn't that break the ability to home the gantry's sides independently? > > That's a huge problem. The gantry isn't going to align itself. > > A relevant point of the context here is this is going into a community shop, > with a constant stream of new users with very limited supervision. So "power > down these axes and mechanically align them" doesn't sound like a viable > option. In the past I've had the stops aligned and ran the gantry into the > stops until both sides' steppers stalled... gently. > > ------------------------------------------------------------------------------ > Transform Data into Opportunity. > Accelerate data analysis in your applications with > Intel Data Analytics Acceleration Library. > Click to learn more. > http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
