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Rack and Pinion (Death to Belts)

Discussion in 'CNC Mills/Routers' started by Joe Young, Dec 9, 2018.

  1. Joe Young

    Joe Young New
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    Awestruck likes this.
  2. Tracy Ranson

    Tracy Ranson Well-Known
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    I really would like to see more of how this low profile rack and pinion could be used with the C-beam and would like to see if Openbuilds would be interested in offering an affordable rack and pinion combo. Either way I would be interested in knowing who supplies the low profile rack and pinion as this is a direction that I would like to take. I think that a helical rack and pinion would be better but if I can at least get a link to the supplier that would be great. I am not an engineer but I know that a rack and pinion set up like this could easily provide a huge improvement to the linear drive mechanics of a DIY machine, not only will it improve cutting capability but it would also greatly reduce backlash
     
  3. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    I suggest moving the rack inside the C-beam. You don't need to add extensions on the wheel spacers that way. Also teeth facing down decreases the potential for debris collecting in them.

    Rack.jpg
     
  4. Tracy Ranson

    Tracy Ranson Well-Known
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    To reduce debris you could also add some sort of brush set up or way covers of some sort.
     
  5. Steve Mc

    Steve Mc New
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    Really like the idea of a rack and pinion system incorporated into the Open-Builds eco-system. one thing I have noticed in other implementations is the use of a pivot and spring-tensioner for contact between the rack and pinion gear. Can anyone (out of interest) give me the reasoning for doing it that way? The only thoughts I had was to compensate for any misalignment or non-linearity.
     
  6. ChadRat6458

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    Wow, I would be interested in this. I don't like the belts either. 8mm lead screws are not that great for long distances. 10mm lead screws would be great. Rack and pinion would be awesome.
     
  7. MCRCNC

    MCRCNC New
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    This is cool, would be useful on larger machines as you can run as many racks as you need.
    I think the spring loading is to ensure optimum contact area with the teeth. I think I've seen you can get backlash with R&P if the gear doesn't touch both front and rear teeth, so any direction change has a minute jump between the two before engaging. I'd say the spring avoids that. The CNC router parts has a spring to pull the gear up (with teeth pointing down).
    Very interested to see where this goes.
     
  8. Joe Young

    Joe Young New
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    Hey MCRCNC,

    Here's the solidworks pack and go of the concept. Mmcaster p/n are located in the assembly tree. Keep in mind that this is just a concept design. Following my goliath upgrades, I'll design and cut a custom plate with 6mm 6061 AL. The current carriage uses a modified C-beam plate, with some cut extrudes for holding the nema23.

    Please let me know if you make any progress before i do. Sharing is caring..
     

    Attached Files:

    Bernie CLark likes this.
  9. Joe Young

    Joe Young New
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    I like the idea. Anything to decrease the moment load on the carriage is a win. Debris could be an issue as well, like you mentioned. The only annoyance is designing around the COTS gear rack and pinion. It gets tricky with the packaging/fasteners when you throw it on the inside. But its worth investigating..
     
  10. Joe Young

    Joe Young New
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    The eccentric nuts and squish from the wheels could cause misalignment, or non optimal gear meshing which would lead to inaccuracies in the steps/mm or backlash. This wouldnt really be a problem with a 3d printer since theres virtually no load, but its an issue with CNCs.
     
  11. Michael.M

    Michael.M Journeyman
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    Interesting concept. Looking forward to your progress.
     
  12. ymilord

    ymilord Journeyman
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  13. CNCMD

    CNCMD Well-Known
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    Add some linear rail and forget the wheels.
     
  14. gmorse7

    gmorse7 New
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    Would like to see this. I like the idea of placing the rack on top inside the C.
     
  15. matt_o_70

    matt_o_70 New
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    I have no means open the file to check the McMaster PN's but I have yet to see a 4 foot (20 degree) section gear rack that is NOT $50 or more each.

    You mention a $20 gear rack - but how long is it or where is it purchased from?
     
    #15 matt_o_70, Dec 22, 2018
    Last edited: Dec 23, 2018
  16. msaeger

    msaeger New
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    I like the idea. CNC router parts says you need a gear reduction with the rack and pinion to get good enough resolution but I see other places say you don't because you can use microstepping but then I read microstepping is bad so who knows whats really true.
     
  17. Adam Filipowicz

    Adam Filipowicz Journeyman
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    I really like the CNC Router Parts R&R System, A gear reduction is needed, even with Microstepping, so we have the torque and resolution needed,
     
  18. Awestruck

    Awestruck New
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    I like this idea and look forward to seeing how you move it forward.
     
  19. Adam Filipowicz

    Adam Filipowicz Journeyman
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    Based on this design, you are using a pinion with 16 teeth/20 Pitch and a pitch diameter of 0.8" so for each rotation the Axis would move 2.513" (63.83mm) if Stepper motor was set to full steps, 1/1 = 200steps
    machine positioning accuracy is 3.13 steps per mm, or 0.319mm /step

    Compared to current 8mm Tr8*8-2p 4 Start Acme screw used, an Axis moves 8mm per rotation, if Stepper motor was set to full steps, 1/1 = 200steps
    machine positioning accuracy is 25 steps per mm, or 0.04mm / step

    We basically need a 8:1 gear reduction for this rack/pinion to match current Acme system accuracy

    Compared to the CNCRouterParts R&P Pro system they are using a pinion with 20 teeth/20 Pitch and a pitch diameter of 1" so for each rotation the Axis would move 3.141" (79.796mm) if Stepper motor was set to full steps, 1/1 = 200steps on its current 3:1 Gear reduction (ie 600 steps/roation)
    machine positioning accuracy is 7.52 steps per mm, or 0.133mm /step

    perhaps the real question is how much position accuracy is really required.
     
    #19 Adam Filipowicz, Jan 1, 2019
    Last edited: Jan 1, 2019
  20. Ianb007

    Ianb007 New
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    Would you be able to save the Solidworks in an STEP file or version that can be opened in 2015 SW?
     
  21. Tracy Ranson

    Tracy Ranson Well-Known
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    Could you please convert the files to DXF or DWG not everyone has Solidworks. Thanks
     
  22. Forestbird Originals

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    I agree with him, which is why keeping a spring-like load on the gear side of the contact would help it to be adjusted as it wears and with any inconsistencies.
     
  23. sunil

    sunil New
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    any progress on this idea, love to switch over to rack and pinion
     

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