Also check out these racks that are screwed in the other way: McMaster-Carr Might be interesting for strength purposes. (And their plastic gears and racks are dirt cheap to experiment with...)
@Rob Taylor Onshape Check out branch B1. Instead of putting the stepper on spacers I just moved the pivot plate out with a 9mm aluminum spacer. It's only a slightly wider footprint but it would definitely give us more flexibility as far as what racks and spur gears to use inside the c-beam. That lets me double the width of the rack and the spur gear and have the rack through-mounted up to the top of the c-beam. I like this idea better.
That looks much more sturdy, for sure. My only concern is the spring/bolt tensioner, seems like just being sprung like that it could be susceptible to inefficient jiggling around the pitch height and uneven wear, or even skipping. Enough tension to hold it against the force of the motor and the spindle might be too much tension to hold the pitch diameter at the pitch height, and rather force the teeth too far into mesh. Would one or two bolts with some arc slots and spacers be a little more of a positive location strategy? Not to mention more manufacturable in terms of BOM, that arm is a whole assembly in itself. Looks cool, but I feel like it would also get in the way of attaching other things to the plate in general- gantry columns, a z-axis, whatever.
Yeah you couldn't attach a gantry column to this setup on the outside of the machine. It would have to be mounted to the interior plate, so it would limit X travel by a little bit. Unless you double the height of the C-Beam Gantry Plate and attach the gantry column to the top part. But I would have some concerns about rigidity if you did that. The spring assembly I basically stole from CNC Router Parts, see below. Seems to work well enough for them. (Of course they're using hardened steel gear racks and I believe aluminum pinions, so it would depend on the materials used for the Openbuilds machine.) I'm not sure what you mean by bolts with arc slots and spacers, do you have an example?
That looks great David! We also are working to stay in the system as much as we can and keep it as simple to build and use in any area of the system. Like Rob mentions above if your able to move the belt system to the outside of the plate using standoffs you may be able to take advantage of having the room for a heavy duty off the shelf rack system which is a nice advantage.
Hi Mark, thanks for the response! I agree, it makes more sense to move the belt outside like I posted above, because it gives us much more room to work with inside the C-beam for the rack and spur gears. This is a link to my branch with an additional 9mm aluminum spacer moving the pivot plate out, so that the belt can be in between the C-beam plate and the pivot plate. Onshape Assuming the Rack and Pinion system is on the exterior of the Y Axis C-beams to mitigate getting chips stuck in the gearing, it does make it difficult to mount the gantry column as you guys typically do on the LEAD CNC. I think it would require a new, longer C-Beam Plate similar to what you do on the workbee.
Not to bring up an old thread, but did you build this? Im currently working on a larger footprint cnc that needs rack and pinion, and even though, i am looking at the delrin internal tslot rack, I will need to do some sort of sprung setup like this. Just wondering if there is some feedback on how well the design worked out.
