Hi all, Since I’m cheap I’d prototype with a fiberglass tube and fill with urethane foam. How much does the modulus change between a rectangular tube and elliptical geometry? Box with corner braces that are viscous damped. It all comes down to load and frequencies. I’m just the aging dummy in the corner. ;-)
> On May 13, 2024, at 2:36 PM, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > > >> On May 13, 2024, at 1:45 PM, Todd Zuercher via Emc-users >> <emc-users@lists.sourceforge.net <mailto:emc-users@lists.sourceforge.net>> >> wrote: >> >> Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam >> on a gantry router without adding too much mass? What is there now is a 4" >> x 8" rectangular 3/8" walled extrusion that is 145" long. >> >> Under normal jogging commands the two servos control the ends of this gantry >> reasonably well, but while the axis is homing the thing shakes and wobbles >> terribly bad. Also If I put a dial indicator in the center of the bridge >> and hit the bridge forward or backward it will flex and wobble enough to >> displace the dial indicator +/-0.03 and it takes nearly a dozen wobbles to >> dampen it. But on the ends the servo's only have a few thousandths of give. >> >> I'm less concerned about the actual stiffness and more worried about >> dampening the wobble. > > > What is the extrusion made of, I assume it is some kind of aluminum alloy. > The simplest but expensive option is to replace it with a stronger/stiffer > material with the same dimensions. Of course Titanium comes to mind but > that is maybe not in the budget. Carbon fiber could work and it is > possible to DIY carbon fiber beams with just hand tools. I have made 4 > meter long racing kayaks with carbon, using just a paint brush and scissors > in one weekend. > > The first class way is to make a female mold and polish it well so the part > looks nice. The cheap way is to make one like they make surfboards. You > start with a foam block, shape it then wrap it in fiber and resin. > > The neat thing about carbon composite is that you are not limited to the > extrusion shape. I would make the entire beam a compound curve with no flat > or straight or cylindrical sections, Maybe like a very elongated American > football but with ovil cross section. > > I like to use the car hood story. A flat sheet of sheet steel is bendable by > hand. But after they stamp it into the shape of a car hood it becomes rigid. > So rather then a square tube, way not oval but with a larger diameter in > the center where all the bending force is? > > The way you make it is to first make a full-size model out of wood and bondo. > Do a test-fit and give it an automotice grade paint finsh and then paste wax. > Make a fiber glass mold, then from that your part. Yes that is a lot of > work. This is why you have an aluminum extrusion there now, because that was > easy and cheap. > > > > > > >> >> Todd Zuercher >> P. Graham Dunn Inc.<http://www.pgrahamdunn.com/index.php> >> 630 Henry Street >> Dalton, Ohio 44618 >> Phone: (330)828-2105ext. 2031 >> >> >> _______________________________________________ >> 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 <mailto: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
