Z direction does not shrink so much because each layer is placed at an absolute position rather than relative to the previous layer. So the only shrinkage you should see in the z direction is the amount of thermal expansion from your build enclosure to ambiant.
XY shrinkage is a common issue with 3d printing. In the Stratasys software that I use, it’s something you set on each print—if you bother changing it, that is. It would be difficult (for me, at least) to come up with a mathematical formula for calculating xy shrinkage. All the recommendation I have seen are to print, measure it, compensate using the scaling controls, and print again. If you find that you use a consistent amount of scaling from one print to the next, you could change the X and Y stepper scale in firmware. Or maybe add a scale factor to your g-code preamble in Cura. But keep in mind that this would change your extrusion rate slightly. [Image.jpeg] Thaddeus Waldner ________________________________ From: gene heskett <ghesk...@shentel.net> Sent: Friday, March 25, 2022 9:15:23 PM To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net> Subject: Re: [Emc-users] Using bb's for ball bearing balls while 3d printing. 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, 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 <ghesk...@shentel.net> > > 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
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