On Friday, 25 March 2022 20:02:34 EDT Chris Albertson wrote: > Real sealed bearings units are not expensive, even large ones with 60mm > or larger boreholes. Look on Amazon the like. > > Here is a random example, two for $15 They would not drop into your > existing design, but you design around them or something like them > amazon.com/uxcell-6812ZZ-Groove-Bearings... > <https://www.amazon.com/uxcell-6812ZZ-Groove-Bearings-Shielded/dp/B082P > Q1NCY/ref=sr_1_7?crid=12OY4CUYLTJ6X&keywords=sealed%2Bball%2Bbearings%2 > B60mm&qid=1648252254&s=industrial&sprefix=sealed%2Bball%2Bbearings%2B60 > %2Bmm%2Cindustrial%2C130&sr=1-7&th=1>
Thats not a bad price, but are also 4mm too wide. Can they stand being forced into an ellipse that makes them around 1.5mm out of round? Thats one of the things my roughly 44mm bore printed bearings can do when printed in PETG. The printed ones are only about 5.92mm wide, stacked 4 high on a 23.9mm tall armature. Thanks Chris. > What I do is first find the cost-effective bearing then design the 3D > printed part around the bearing. You can press-fit the bearing to > the plastic. Sometimes the pocket in the plastic is not round enough, > so I place the plastic part in the lathe and bore just a tiny bit out > to true the hole. > > I tried printing bearing races, they never work well But pressed-in > bearings do. I've got a dozen of them here Im installing on a robot > quadruped. The total cost is scary though. If I break this one and there is no possability of a salvage/repair, I can print another from scratch for around a tenner in materials. Thats a pretty strong incentive to make it Just Work. The one at hand is developing some backlash, half a degree maybe, but also has about 120 days of running at about 2 or 3 rpm output on it while sitting on my kitchen counter. I could probably get rid of the backlash by replacing the armature bearings with better fitting ones that won't wear as fast because the loading is more even over the width of the race. Currantly its the outer edges of the race thats catching the majority of the loading which is 99.9% radial. What red you see in the pix I posted is the result of a 3% x shrink which has now been incorporated in the .stl. But hasn't been printed yet. Thats next, for spares when this one finally fails. > On Fri, Mar 25, 2022 at 1:29 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 > > > > _______________________________________________ > > 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 > . 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
