On Fri, Mar 25, 2022 at 7:19 PM gene heskett <[email protected]> wrote:
> On Friday, 25 March 2022 16:59:37 EDT Thaddeus Waldner wrote: > > I would suggest that you calibrate the xy shrinkage, and z shrinkage in > > your printer slicer, instead of compensating for it in your design. > > Cura doesn't make that obvious as how to do that, I think the only way is "M92" g-code. https://marlinfw.org/docs/gcode/M092.html Place this is the boilerplate that goes before each print. One thing I've been meaning to do is place a dial indicator on the print head and very the steps per mm on x, y, and z. The problem might not be shrinking but cheap belts made with a tiny error in pitch. > and AFAICT there is no > shrinkage or growth in Z. Its finest z layer is .12mm all the way up, or > dynamic depending on the layer but its not plain what might trigger the > thicker layer. If I tell it to make a part to fit inside a 24mm internal > housing with .125mm movement clearance on each side for two parts > totalling 23.85mm tall, it will measure 23.81" high for the stack when > done. That's about the right room for some synthetic plastic grease... > > My reticence to messing with cura is that this is an end to end fix, and > that fix also adds that red layer of thickness to the actual plastic laid > when making the bearing races, making it stronger yet. Perhaps in newer > code I might fix cura if I knew precisely how to fix it instead. > > This is all part of my $10 material cost for a miniature harmonic drive > to add to the 4th axis of a 6040 gantry mill. And I am probably going to > wear it out making a wooden (hard maple) vise screw for a woodworking > vise, I've already made the buttress thread nut, a 12mm pitch, 2 start > affair on the 3d printer. Now I have to make the screw that fits it. And > then design and print the thrust bearings. > > If you are familiar with how to make cura do that, plz advise as it would > be nice to spec a ball 4.35mm in diameter like a bb measures, to cut a > ball track, instead of the 4.56mm I'm currently using for such. Any less > and its too tight a fit, won't roll well and will split either track at > the center, thin place before it rolls very far. > > Thank you Thaddeus. > > Take care and stay well. > > > > On Mar 25, 2022, at 3:29 PM, gene heskett <[email protected]> > > > wrote: > > > > > > Greetings all; > > > > > > It has come to my attention that one of the potential failures in my > > > harmonic drive with a loose belt experimentation, which seems to be > > > caused by the unequal shrinkage in the xy direction as opposed to the > > > z direction is at least partially caused by the nozzle diameter. If > > > I attempt to achieve a zero clearance bearing simply by shrinking > > > the dummy ball from about .5mm bigger than the bearing, as it > > > shrinks, the wider edges of the bearing groove come into zero or a > > > slight preload condition, leading eventually to a race fatigue split > > > at the center of the races width. Working in openscad, a scale > > > command would fix this by shrinking the bb shape used for clearing > > > that groove, only in the x direction. > > > > > > Th question is how much would it take to transfer the majority of the > > > stresses on the race from being on the outer edges of the race, to be > > > more concentrated on the center of the race, with an eye toward > > > reducing the splitting force on the bearing race. > > > > > > 1% x shrink, 2%, 3%, what would be the ideal amount of shrink to > > > compensate for the printers .4mm nozzle, being used to only lay .12mm > > > per layer? > > > > > > Seems to me there ought to be a way to mathematically predict how > > > much > > > that shrinkage diff there is. Attached, an extra 2 lines to draw that > > > away from the bearing itself, showing how little the difference is > > > for a .97 x shrink. > > > > > > Comments plz? > > > > > > Cheers, Gene Heskett. > > > -- > > > "There are four boxes to be used in defense of liberty: > > > soap, ballot, jury, and ammo. Please use in that order." > > > -Ed Howdershelt (Author, 1940) > > > If we desire respect for the law, we must first make the law > > > respectable. - Louis D. Brandeis > > > Cheers, Gene Heskett. > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author, 1940) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > > > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
