A printable, high speed alternative to belts?

Years ago, I created AoI scripts to design involute profile gears and racks.  Recently, I've been exploring the notion of using rack and pinion drives instead of belts.  While it is relatively easy to design and print a rack and pinion gear set, conventional ones have a problem with lateral stability.

I soon found that I was buying far too many skateboard bearings to make up for this problem than was sensible.

A month or so ago, I ran across the idea of herringbone {double helical} racks and gears.

You don't hear too much about this kind of gear and rack mostly because it can't be machined with conventional hobbing machines.  It can, however, be printed relatively easily.  I found that I could coax my extant rack and gear scripts to produce such components.

I was at, however, pretty much the limit of what Art of Illusion could handle.  By the time I converted an involute gear profile or a rack to a triangle mesh then extruded and did a few boolean ops on it even the improved power of AoI 2.8 was barely up to the job.

While I could typically make herringbone gears happen the racks were a real trial.  This had a bit to do with the fact that a rack profile does some really strange things when you apply AoIs triangle mesh routine to it.

You could extrude that and only get webbing on the outside surfaces.  As you can see, however, you get lots and lots of triangles from AoI.  I soon found that I could not make herringbone racks with more than about 12 teeth.   It was easy to see with a rack that you ought to be able to describe it with relatively few triangles, so I gritted my teeth and decided to go directly to a solid description.

Using the Platonic Solids script as a point of departure, I began to develop a herringbone rack script.

I finally got the whole thing going during lunch today.

I checked the resulting STL in Netfabb and determined that it was perfect.

I developed a 12 toothed 10 mm radius herringbone rack and pinion pair.

This configuration gives you about 0.3 mm/step when you attach a 1.8 degree stepper to it.  Gear that down by a factor of 3 using another herringbone gear pair and you've got the 0.1 mm/step standard Reprap resolution.

Herringbone gears are pretty much naturally anti-backlash.  They seat firmly, are quiet and have strong lateral resistance.  They're printable and there is no reason whatsoever why you shouldn't be able to use them instead of a belt.  I printed up a 130 mm rack and pinion set this evening.

The racks can also, since they are very thin, be printed in long lengths without warping.  Using a 0.3 mm extruder orifice and printing at about 16 mm/sec I completed the rack in about an hour and twenty minutes and the gear in 45 minutes.

I've been able to make rack and pinion sets with gear finenesses of 24 teeth for a 10 mm radius.  That's really pushing the envelope, though.  It appears that 20 teeth for 10 mm radius is a practical limit.

I intend to clean up the rack script and write one for the herringbone gears now that I know that they work well.  I will make the scripts available as soon as I have them cleaned up a bit.

This experience has brought home what I consider a very important point for me.  We need to be looking for technologies that aren't necessarily cheap or usual in metals.  Such components are dependent on purpose built milling machines.  Our printers are much more flexible than that.  We need to choose technologies to print with that in mind.

Friday update:

I queued up a 267 mm rack while I was working this morning. No warping.

Not bad.