On 8/25/2014 8:58 AM, Gene Heskett wrote: > Do not underestimate the rotational rigidity of an 8oz piece of 1.5" or 2" > tubing in 22ga steel, such as that used for a swing set leg. For shorter > runs, alu tubing in 1/16" wall thickness is available in up to 1" od and 8 > feet long at your local lumber yard. One could also use EMT conduit, > comes in 10' lengths but its at least 2 gauges heavier. With suitably > machined steel inserts super glued into the ends to bring it down to a > size suitable for bearing mounts and couplings to allow for thermal growth > lengthwise, the rotational mass is fairly low, and torsion induced > twisting would be well below being a concern. > > The mass of a solid rod can easily be reduced 90%. And 95% isn't > impossible.
If you want more Z height, you can raise the gantry rails (as this table is made) or use a drive chain at each end down to drive the pinions on the racks. Or skip racks and leadscrews and use stationary chains looped up around idlers to the drive shaft as high as you want. https://www.youtube.com/watch?v=vETkf1sqo3M Yet another way to drive a tall gantry with low side rails would be a vertical shaft at each end with bevel gears to go around the top corners and mounting racks and pinions vertically at the bottom. Still another method is to use a leadscrew or ballscrew along both sides and connect *both* ends with chains. One motor in the middle of one end can drive it. I once saw pictures of a very old metal lathe that had a leadscrew on the front and back of the bed, with both ends geared together. Same concept, the power drive gears only had to go to one leadscrew gear from the spindle at the headstock end. The double shafts and gearing ensured the carriage could not twist at all on the bed. There's so many ways to mechanically link two sides of a gantry, and if you still have issues with it getting out of square then it wasn't built rigid enough. This Torchmate has an aluminum gantry and the motors are only NEMA17 size with cogged belts on reduction pulleys. I'd have to count teeth to know how much reduction. Rapids are plenty fast and it's not intended to push anything but a plasma cutter, so huge amounts of torque aren't needed. The cross drive shaft is ~3/4" ACME rod, driven at one end, with rack and pinion at each end. Could be ACME threaded rod was used to have a torsionally stiffer rod while somewhat reducing weight. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
