Here is a design I am thinking of using for my rack and pinion drive. My original router design used R&P, didn't work because there was no spring putting tension on the rack. It would work itself loose and screw up my pieces that I was cutting. I am going to basically build an arm and use a spring to press it up against the rack, similar to other designs I've seen around here. This arm will be made of MDF, using bearings around the pivot screw and the motor shaft. In the future I will replace this with aluminum, and may gear it down, but I was happy with the resolution and torque before, so I'm sure it will be fine.
Why do this? To fix the rack setup in the first place I replaced it with 1/2-10 acme screws. Well, now it's slow. Accurate, but very slow - 30ipm max. I'm sure most of this is adjustment, but even if that is perfect, I will not get even 80ipm. Multiple start screws are expensive. I already have this rack setup, and even gearing if I want to gear it down. Live and learn.
Specs: I will be using 1.5" MDF plus another 3/4" to mount the motor so there is clearance for the setscrew so it does not interfere with the bearings. The bottom of the rack is about 5.25" below the bottom of the side of the gantry. The arm will be about 11" long. I am using a 5/16" bolt and the same size skate bearings for the pivot arm (that's what I have laying around). I will be using a 1/2" shaft to connect the motor to the pinion, and the same size bearings to support the shaft. The arm will essentially be pulling up on these bearings.
Please excuse the drawing, I can CAD only enough to sell my products.
My questions -
Is there a more efficient lever design than this? Without actually building/testing, it seems like it will take a significantly strong spring to apply enough pressure.
Will the bearings I plan to use be sufficient?
Any other suggestions? Anything I havn't thought of?