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OpenSCAD Roller Pinion Rack Profile

by dammitcoetzee, published

OpenSCAD Roller Pinion Rack Profile by dammitcoetzee Feb 25, 2012
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Summary

Apparently there's this great thing out there for linear motion called a roller pinion. It has all of the advantages of a rack and pinion for simplicity, but it'also precise, has low backlash,is efficient, and quiet.

I spent some time trying to figure out how to derive the profile. I believe I'm really close to the right profile. I'm hoping others can help me make it a real thing.

It would be nice to use these for anything that needs precise linear movement.

I'm thinking that for the rollers you could use smooth rod and some brass tubing from a hobby store (for bushings).

Here is some of my reference material.
http://www.ecnmag.com/articles/2011/07/hardware-corner/roller-pinion-tech/

http://www.nexengroup.com/nxn/files/pdf/966650s.pdf

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Looking at the STL that is uploaded and that gets generated, there are 'faces' between each tooth which will make the rack NOT manifold nor one piece. Some work needs to be done to do this properly/differently.

I've attempted to make a different version of this here: http://www.thingiverse.com/thing:1013816

This attempts to create the profile by having the pinion cut the whole rack at once instead of generating individual teeth. It does take a long time to generate (1.5 hrs on a 2core 3.6ghz computer) the rack but it is mostly if not completely parametric. I'd love to see what you think.

Roller Pinion and Rack

For the rollers, maybe take apart some roller chain (motorcycle chain). It has an inner shaft and outer roller perfectly sized.

This would be good for the Prusa Y axis.

Try to make a section of the rack with ends like a jigsaw puzzle so they can be slotted together for precision placement. You'll also want a printable dist with holes for aligning the tubes. Better yet, print a lantern pinion at the right size to match the rack. Don't forget to put a hole for a set screw to attach the pinion to the motor shaft.

I hope your code makes it easy to customize:

  • number of rollers
  • size of rollers
  • diameter of pinion
  • diameter of pinion center shaft (for motors)

and sizes the rack accordingly. For added challenge, try a circular rack. (the pinions get really fun.)

Some good ideas, I'll take another look at the project and see if I can get further. This was literally my first time picking up openscad, so I'm sure I need to start by simply rewriting what I have. Haha.

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