I had only eyeballed the equations, not plugging in numbers and figured it was a toss-up. Put you can always modify the tube and turn it into a solid. Simply fill it with chopped carbon or glass fiber and epoxy paste, pack it in and let it cure. I've made parts with before and they are very stiff and strong. The random fiber orientation is not as bad as you might think and even short chopped fiber still has 100+ length to diameter ratio. The key is is mix in as much fiber was physically possible while still getting it all to wet-out.
This is a quick way to make parts, faster and stronger than 3D printing. Model makers have been doing this for decades. I was making small parts for flat-water racing kayaks with fiber-filled resin and latex molds So unless the tube needs to have light weight, just fill it and make it a solid. Or use a larger aluminum part On Mon, Dec 5, 2022 at 4:03 AM andy pugh <bodge...@gmail.com> wrote: > On Mon, 5 Dec 2022 at 02:20, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > > and we don't even know the exact kind of steel in the rod. Without > knowing more it is a toss-up. > > You don't need to know, all iron alloys have the same stiffness (to within > a couple of percent). > The shear modulus (G) for steel is 80 and for carbon fibre is around 5. > Steel is a lot stiffer than CF. > > Anyway, with a 2Nm motor you might see 1.7 degrees of twist in an 8mm steel > shaft which is 500mm long. > Playing with numbers it would be 3 x less with a steel tube 12mm dia and > 1mm wall thickness. > To match the stiffness of the steel bar with a _round_ carbon tube it would > need to be 20mm dia and 1.5mm wall thickness. > > https://amesweb.info/Torsion/torsion-of-shaft-calculator.aspx > > Note that there is only any torsional load on the shaft when accelerating, > so the extruder will generally not deviate from the path very much, but > will be lagging along the correct path. > (This is true of milling machines too, the f-error is typically > approximately along the path, so has less effect on part geometry than the > raw numbers would indicate) > > -- > atp > "A motorcycle is a bicycle with a pandemonium attachment and is designed > for the especial use of mechanical geniuses, daredevils and lunatics." > — George Fitch, Atlanta Constitution Newspaper, 1912 > > _______________________________________________ > 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
