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
