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Rack & Pinion

Discussion in 'CNC Mills/Routers' started by Adam Filipowicz, Aug 12, 2017.

  1. Adam Filipowicz

    Adam Filipowicz Veteran
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    Has anyone built a rack & pinion system with Vslot. I would love to see how it was done and what parts were used.
     
  2. Jonathon Duerig

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    Yes. I used C-Beams from Open Builds with the 'pro' rack and pinion stuff from the CNC Router Parts store. The rack has a flange that you can screw into V-Slot with M5 screws + fender washers. The flange is longer than 20mm, though. So your guide consists of a C-Beam attached to a 20x20 or 20x40 V-Slot beam, making the whole thing 40x100. There is enough space inside the C-Beam interior for both the rack and the pinion gear. I created custom steel plates for both my X-axis and Y-axis gantries (4 plates in all). And I use an Open Builds acme screw with a C-Beam for the Z axis. The other gotcha with this setup is that my steel gantry plates ended up being 250mm wide (the rack and pinion setup is large). So my 1000mm x 1000mm machine ends up having a travel of 600mm x 590mm or so. I have plans to tweak the design to let it cut 600mm x 1200mm without increasing the footprint much, but I'm still working out details.

    If you want to go in this direction, let me know and I'm happy to give details. It has greatly speeded up my original design which used acme screws on every axis. At this point the limiting factor is my controller (an xPro 2) which can only give so much juice to the steppers. But even now I can easily move 2000mm/min on the Y-axis with no chance of a skipped step. And I can go double that on the X-axis. I cut plastic, but everything is solid enough that I think it can likely cut wood easily as well.
     
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  3. Adam Filipowicz

    Adam Filipowicz Veteran
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    Please do share any photos or drawings you have of your setup. im very interested.
     
  4. Jonathon Duerig

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    Photo Aug 13, 8 00 25 PM.jpg Photo Aug 14, 8 48 48 AM.jpg Photo Aug 14, 8 48 56 AM.jpg Photo Aug 14, 8 49 06 AM.jpg Photo Aug 14, 8 49 11 AM.jpg Photo Aug 14, 8 49 16 AM.jpg Photo Aug 14, 8 49 25 AM.jpg I keep meaning to do a proper 'build' writeup. But so far I just haven't found the time. See some attached photographs of the setup. One peculiarity that you might notice is that everything is 'upside down' from how things usually are. This was because my original plan was to have this CNC cutting bed be the bottom of a double-decker CNC machine to allow me to cut two things at the same time and conserve floorspace. But the new machine ended up being so fast that the parts for my second cutting bed which was to sit on top of this are gathering dust atm. I will likely add on a second CNC machine on top at some point.

    You can browse the CAD setup I used to create the custom gantry plates here: Onshape

    I can send DXF files of the custom gantry plates if you want to cut them out exactly the same way yourself. I paid to have them lasercut out of 3.4mm (0.135") hot rolled steel then spray-painted them black. They could be cut out of thicker aluminum as well.
     
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  5. Adam Filipowicz

    Adam Filipowicz Veteran
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    Thank you so much. I was literally drawing up a very similar configuration last night on paper.

    Are you aware of cad files for cncrouterparts parts. Made by them?
     
  6. Grantman

    Grantman Veteran
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    It appears that you have ample room to mount the flange on the backside of the rack and then bolt the flange inside the C-beam.
     
  7. Jonathon Duerig

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    @Adam Filipowicz I downloaded the 3d models of their parts from their website and used them when designing my setup. Just look on the store page of the item in question and scroll down to the 'Plans' section. The only problem I had was that their 3d model of the rack didn't have an accurate flange size. The flange was larger than specified which is why I added an extra V-slot to the rail instead of just using a C-Beam alone.

    @Grantman I hadn't thought of that. It could work. The downside is that the gear wheel would only partially mesh with the rack. You'd need to make sure there was clearance for the screws/washers. And this would tend to increase the wear of the system. But on the plus side it would be more compact and remove the need for an extra V-slot rail attached to the C-beam. It would also be necessary to verify that the mounting screw positions would still align well enough with the slot. The holes are oversized compared to M5 screws, so they don't need to be precisely aligned.

    -D
     

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