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Discussion in 'CNC Mills/Routers' started by Joe Young, Dec 9, 2018.
Low profile rack and pinion linear actuator design
Joe Young published a new build:
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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
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.
To reduce debris you could also add some sort of brush set up or way covers of some sort.
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.
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.
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.
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..
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..
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.
Interesting concept. Looking forward to your progress.
Did this a couple years ago.
Kyoujin Mk1 (C-Beam /w Rack & Pinion)
Add some linear rail and forget the wheels.
Would like to see this. I like the idea of placing the rack on top inside the C.
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?
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.
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,
I like this idea and look forward to seeing how you move it forward.
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.
Would you be able to save the Solidworks in an STEP file or version that can be opened in 2015 SW?
Could you please convert the files to DXF or DWG not everyone has Solidworks. Thanks
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.
any progress on this idea, love to switch over to rack and pinion