I hope Whosa Whatsis approves. 
I just finished a Fully Rack & Pinion Wallace design.
The prints have been coming out beautifully.
The parts are on thingiverse and I’ll be building some for sale over the next few weeks.
I’ll make another post if someone wants to see print samples.
I’ll also be putting info up on my website later today.
http://gkprotoforms.ca
I intended early on to try rack/pinion for the Y axis, as that’s essentially how the belt is being used anyway. Adding the weight of the X motor to the X carriage seems a little silly, though 
It would increase the space required, but couldn’t you extend the x-axis rack to one side and mount the motor/pinion to the side? I’m no engineer, but that thought popped to mind.
Nice work.
very tasty job. well done Lance. With the backlash and stretch of belts eliminated would be ideal for mounting a dremel to make a mini cnc mill.
Awesome.
Yes, @Carlton_Dodd , you would need a rack 2X the length and more space, but you could mount the X motor off to the side.
You might consider adding a bearing to run along the back of the rack to keep it from deflecting and skipping off the pinion.
@Russell_Nelson you could move the motor to the side with the same length rack. The travel is the same as in the video. The rack would be sticking out the side of the printer when the carriage was on the near side.
That thing is lovely! I’ve been noodling on more printable alternatives to belts, cables, etc.
When I considered the precision of 3d printed rank/pinion systems and how to improve it, I actually planned to try attaching a timing belt to a flat surface to make the rack. Of course, this was in the days when getting very large or accurate prints was much more difficult, and before there were libraries for generating herringbone gears.
Good work. How long is the rack?
@Wylie_Hilliard Yes, I see what you mean. The rack needn’t be longer, but the space it consumes still needs to be 2X as wide.
I like the idea that there is no belt, no idler tension etc. How does it handle having two motors on the X carridge, with the extra weight?
That seems like the biggest problem: adding mass to the print head. You could reasonably put the X motor off to one side and extend the rack, but that double the operating width of the printer. Or you could mount it on a bridge over the middle, but that introduces complexity because you have to connect a long rack to a small print head in the middle.
Or put the x motor on the table and turn a smooth square rod (or anything that isn’t fully round) on which slides a herringbone gear that meshes with your rack. Make the rack two sided and add idler herringbones to connect either a z carriage or lead screw…
I’ve thought about printed rack and pinion, especially for Z, but many people have said that the accuracy for small details is not good enough. Is this not the case?
Also, I thought there was the problem of a printer using a printed rack would produce a rack slightly worse than the one its using, so no good for replicating robots?
Thanks for all the comments.
The reason the motor is on the X-Carriage, rather than its normal place, is I didn’t like the Prusa R&P designs I saw with the bar sliding out the side of the machine.
I thought it dangerious and I really don’t have that much room for my machines as they are.
So, I really wanted a design that fit within the machine.
As to the flying motor idea, Yes that would make for a lighter X-Carriage, and I can think of a couple ways to mount it, but it’s a little more involved to set up that way.
What I like about this design is, the X-Carriage is now ballanced. One motor on each side.
So far, the extra mass, hasn’t been an issue. Probabily partly due to acceleration/deceleration in the firmware. Also, I think because the motor body naturally wants to move in the opposite direction when the shaft moves.
As to the detail issue, I don’t see how to post pictures to the comments or add them to the original post, So I’ll post some links here:
Done with the X belt
Done with the Rack & Pinion 30mm/s
R&P 48mm/s
@Wayne_Friedt
The Rack is 210mm.
I print it diagonally on my 200mm bed.