If there is an error, my bet is the parametric pulley designed program has a bug and/or the author made some simplifying assumptions and the tooth profile is not perfect. You would have to verify the program is correct. Do this by comparing a generated pulley to a same-size pulley design that is downloaded from SPD/SI or McMaster Carr. I bet there is a difference at the <1% level. Take one design and overlay it with the other in your CAD system and any difference should be visible. I'd be surprised if a parametric system was perfect because the commercial pulleys are the result of much testing and tweaking.
The other issue is that 3D printers are not precise in that some of the surface is printed below the ideal surface and some above so there is a random texture added to the ideal part. A belt would tend to ride in the high spots. All gears and pulleys I print need some amount of post-processing to remove the high spots. #600 wet/dry sandpaper works well. Printers never make perfect surfaces. It is very unlikely that your printer is making (say) 99.9% scale models of yor parts. It is using stepper motors and toothed belts, steppers always do the commanded number of steps and timing belts don't slip and always do the integer ratio of teeth, even if the size is off. Now back to the pulley you are printing. Why care about a slight size issue? As long as the belt never slips a tooth the pulley ratio holds. Only with plain pulleys does a tiny size error cause a tiny error in speed reduction. Timing belts are like gears, it is the ratio of the teeth that matter. On Sat, Feb 13, 2021 at 2:06 AM Gene Heskett <[email protected]> wrote: > Greeting all; > > Messing around with the parametric pulley designer, I have made a larger > 86 tooth pulley for the big pulley on the A axis supplied with the 6040 > mill. I'll also change the belt pitch as its presently a huge XL. > > But the chosen belt, a GT2_3mm, is not a good fit, throwing a just > detectable slack in the center of the wrap, inicating the pulley is > about half a red one too small. > > Is this a good excuse to add a couple counts to the xy scales in the > printer, or to play with the variable > > additional_tooth_width = 0.2; //mm > > in the openscad recipe? > > Doing this in PETG, so the ender-3 is at the top of its heater range, > with a 250 degree nozzle and a 70 degree bed. And around 7 rendering > hours to try a new fit. > > Thanks for any advice. > > 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) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > _______________________________________________ > 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
