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Planetary Gear Bearing: Now With Knurling!

OK, I couldn’t resist. Tweaking a few lines of code wrapped a knurl around emmitt’s Gear Bearing¬†for enhanced griptivity:

Knurled vs original Planetary Gear Bearing

Knurled vs original Planetary Gear Bearing

That image has desaturated red to suppress the camera’s red burnout. It looks better in the realm of pure math:

Planetary Gear Bearing - Kurled - solid model

Planetary Gear Bearing – Kurled – solid model

Reducing the tolerance parameter to 0.4 produced a surprisingly rigid, yet freely turning, bearing that required no cleanup: it popped off the plate ready to roll!

The heavy lifting in the OpenSCAD source code remains emmitt’s work. I replaced the outer cylinder with a knurl and simplified his monogram to stand out better amid the diamonds. This is the affected section:

... snippage ...
translate([0,0,T/2]){
	difference(){
//		cylinder(r=D/2,h=T,center=true,$fn=100);
		render(convexity=10)
		translate([0,0,-T/2])
			knurl(k_cyl_hg=T,
			k_cyl_od=D,
			knurl_wd=5.0,
			knurl_hg=5.0,
			knurl_dp=0.5,
			e_smooth=5.0/2);
		herringbone(nr,pitch,P,DR,-tol,helix_angle,T+0.2);
//		difference(){
			translate([0,-(D/2+4.5),0])rotate([90,0,0])monogram(h=10);
//			cylinder(r=D/2-0.25,h=T+2,center=true,$fn=100);
//		}
	}
	rotate([0,0,(np+1)*180/ns+phi*(ns+np)*2/ns])
	difference(){
		mirror([0,1,0])
			herringbone(ns,pitch,P,DR,tol,helix_angle,T);
		cylinder(r=w/sqrt(3),h=T+1,center=true,$fn=6);
	}
	for(i=[1:m])rotate([0,0,i*360/m+phi])translate([pitchD/2*(ns+np)/nr,0,0])
		rotate([0,0,i*ns/m*360/np-phi*(ns+np)/np-phi])
			render(convexity=10)
			herringbone(np,pitch,P,DR,tol,helix_angle,T);
}

I also added a few render(convexity=n) operations to improve the preview, but that’s just cosmetic.

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  1. #1 by madbodger on 2014-01-03 - 09:19

    Pretty!

    • #2 by Ed on 2014-01-03 - 10:17

      It is absolutely the best 3D printed fondletoy ever!

      Maybe someday I’ll come up with something that nice… [sigh]

  2. #3 by Jason Doege on 2014-01-03 - 14:21

    Is it mechanically useful? Also, what is the apparent glitch to the right in the rendering?

    • #4 by Ed on 2014-01-03 - 15:22

      Is it mechanically useful?

      Emmitt designed it as a fully printable rotary bearing, after seeing how poorly low-resolution printed ball bearings work. Comments on Thingiverse say it’s good down to 20-ish mm OD, which would work for toy cars & trucks.

      It’s surprisingly stable, although I’m not sure how durable it is. The tolerances would certainly open up as it wears in, so you’d probably want two bearings on an axle, rather than one in each wheel hub.

      the apparent glitch to the right

      That’s his monogram: EL. I thought about changing it to EN, but it’s his design, not mine…

      • #5 by madbodger on 2014-01-14 - 09:07

        I suppose you could also think of it as “Engineer, Larval” although it’s no more her design than yours.