Hey Guys Ive been skimming the board looking for Rack & Pinion ideas I would like to come up with a design that will nest in and centre itself into V-Slot channels looking to start some brainstorming/discussion I am no engineer,, just a hack with Fusion 360 so if someone can draw this up better please do! perhaps we can get this spec'd out and have a company produce them for us. using 20 pitch/20 pressure angle for this mockup let me know your thoughts holes to be 5mm Diam with 9.2mm for head to clear, 3mm depth Spacing 50mm apart Machined ends so they can be stacked Thoughts on making these from Aluminum instead of steel these parts originally came from McMaster Carr McMaster-Carr McMaster-Carr
there was a thread of a possible uhmw rack with brass pinion a while back..But the pics were censored out of openbuilds Aluminum has bad wear characteristics, makes for black residue all over everything.. and for strength nylon or uhmw is good enough with superior wear resistance with no lube requirements. But yes this has to happen some day! I played with the idea of making my own rack sections out of 1/4" HDPE, even made a sample that worked out well, but i would have to make a bunch of it and build another system to test it!
The CNC Router Parts rack and pinion works well with C-Beams. That is how my current machine is set up. Steel racks, steel wheels. It isn't terribly cheap, but probably cheaper than custom fabrication.
I agree the cnc router parts ones are very good, But there are a ton of chinese suppliers who make plastic racks that would suite our load needs, just a matter of finding one the right size and quality.
also the CNCRouterparts Belt reduction looks very large.. hoping perhaps for a direct drive.. or gearing down a Nema 23 via 5:1 planetary or worm gear.
Hey guys, I want to jump into this discussion. We have been working on this goal as well in hopes we can all work toward an idea that we can call an OpenBuild standard. Racks are the logical next step for the OpenBuilds system and it would be great to be able to use something pre-made to save on custom but I think the advantage of making them to spec designed for the system will have its own benefits. Staying true to the OpenBuilds way with the idea of keeping it simple we were thinking here of spring tension direct drive (use motor tuning to get proper accelerations) Also thinking less thick racks especially with steel, which to be honest in it self may be over kill for the system, but trying different materials that allow for out side use as well as smooth operation, for instance nylon racks. Lets remember all the cool things we are already able to do with the belt and pinion style system so racks will only be an added plus to the ideas of machine building. We have been experimenting with a few ideas but most are over kill steel racking so we want to hear some of the applications and ideas you guys may have. This is a great discussion and a look forward to seeing how it weighs out.
We would need a rack that had screws in the bottom of it, the heads of which would, as in the style above, slide snuggly into the slot beneath it, and then simply put a plate at each end, holding it in place. SIMPLES!
Since most of these machines are fairly low load, looking at other materials is a good idea.. how about Delrin, its easy to machine.
Adam, this is the same machine I mentioned in another thread about this about a year ago: https://openbuilds.com/threads/rack-pinion.9874/#post-57134 Coming up with systems explicitly designed to work with C-Beam seems like a good idea, though. When I did this, I was mostly concerned about what I could build myself based on what was available. If there had been something available that explicitly made for use with OpenBuilds, it would have reduced my nervousness would have obviated a few workarounds I had to do to make everything work. If somebody wants advice and confidence about what works for making a machine today with CNC router parts and C-Beams, I'm happy to advise. But in the longer term I'd love it if there were standard rack-and-pinion plates and parts available at the OBPS. Regarding materials, the benefit of steel here isn't the strength, IMO, it is the durability. Right now the plastic wheels are the weakest link in the system in terms of long term durability. When I rebuilt my machine last year, I had to replace all of them. And I expect to need to replace them again at some point. I would expect a plastic rack-and-pinion system to wear even faster. But the disadvantage of steel is weight. I need bigger motors just to move my gantry around even when not carving. I'm not sure the right trade-off here. But atm, the steel works well for me. I'm not sure what the best gear reduction is. I think the CNC Router Parts are 3:1 for NEMA 23 motors. It is precise enough that the only issues I have with reproducability are if the material itself moves or deflects. And it moves fast enough that I don't feel like the rapids are slow. But if somebody presented me a machine with direct drive or with a 5:1 reduction, I don't know that I'd really notice. -Jonathon Duerig
Delrin could be an option but to be honest although POM will give us great sliding wear, we need a higher impact as well and like Jonathon mentioned on a rack you would not want the wear that delrin will give.. We were thinking of going much harder and testing out NYMETAL or nylon66 it has high wear. The idea would be to use perhaps aluminum rack with nylon 66 pinions if replacements are needed years down the line it would be an inexpensive pinion and not the whole rack. just ideas at this time, but testing will tell a lot more.
Look great @Adam Filipowicz can you share more info on this rack and pinion. I would love try it out this side as well. Thanks man
Checkout Motiontek | Rack Pinion Spear Gear drives CNC Plasma Router Canada USA http://www.motiontek.ca/pdf/PHC.pdf http://www.motiontek.ca/PDF/RHHC.pdf
Hello Gary and Adam, The above images were just a design and never produced due to the lack of interest. Gary found the "uhmw rack with brass pinion" topic with no Images so I though to post them again.
Thank you, can you share the design files with me? also what Pitch is this rack and how many teeth are the pinion?
Sorry Adam, I can not share the design as it is not sold on openbuildspartstore.com or an OpenBuilds design, also still Alpha. Please continue with what you were doing, seems there is some interest for your design. The images show a Module 1 rack and pinion, the rack is 410.7mm long, 10mm in height, 20mm width. Pinion is 20t, 19mm width custom made.
Hey Mark Have you guys made any progress with a Rack system? Would like to buy a Openbuilds Bolt on Standard kit
We do have one in the works and we have been testing it for a while now with great results. The main objectives are make it as modular as possible so that it does bolt right on to the OpenBuilds system and of course can easily be modified for custom lengths. We also needed it to be robust but without the overkill of steel racks. All of this while making it as affordable as possible. These challenges have given us a unique system that we are excited to share soon. In the meantime I am looking for some help with beta testing @Adam Filipowicz if your interested pleases shoot me a message. We will be sure to share news with you guys as we approach a more finalized design. Thank you
Does anyone have any experience with this company? I'm really intrigued by the low cost of the helical racks and I almost don't believe it. On big name suppliers that will remain nameless they charge an arm and a leg ($500+) for commercial grade 1m stock length.
Any updates on the rack and pinion design? I have an MPCNC but am interested in getting something more robust. If I had the money and space I'd get an AVID CNC/CNC Router parts one, but I just found you guys and am really intrigued. I'd definitely like the modularity and stiffness of a rack and pinion motion system vs a belt driven or screw driven one.
Hi David, thank you for your interest and support. Yes the system is still in development and we share the news as soon as we can.
@Adam Filipowicz @Mark Carew Ok guys, I've put quite a bit of thought into this in the last few days, and I think I came up with something that could work. Curious to know what you guys think. Is this close to what you guys are doing Mark? Onshape The upside is that I used as many Openbuilds parts as I could to keep it within the same ecosystem. The bad news is, this design would require a custom rack and spur gear/timing belt pulley combo. I couldn't find something off the shelf that would work. I'm thinking the best way to test it out would be to 3d print them in nylon. Other than that, it would just take a few custom 6mm aluminum plates that would need 1-sided machining. It works on the same principle as the CNC Router parts rack and pinon, just on a smaller scale. The blue plate pivots on the right 5mm bolt and is tensioned by the grey bolt and spring on the left. I included slotted mounting holes for Nema 17 and Nema 23 steppers. Note that I didn't include every single fastener in the assembly. It should be pretty easy to infer where you need screws that aren't shown. Outside view: Some math: 16 tooth spur gear has a 50.265mm linear travel per revolution. With the 3:1 included gear reduction for the timing belt pulley, that gives us 50.265mm/3 = 16.755mm of linear travel per stepper axle rotation. With a 200 step/revolution stepper, that gives us 16.755/200 = 0.0838 mm/step. (And that's without microstepping!) Inside view with the C-beam hidden: The 5mm x 15 long bolts to mount the rack to the C-beam are a little long, but that's easily fixed. There are a pair of Openbuilds standard bearings on either side of the spur gear/timing belt pulley combo so that it can spin freely on its 5mm bolt. Clearance view side 1: Clearance view side 2: Non-openbuilds BOM: 3d printed rack 3d printed pinion/spur gear combo 146mm GT2 timing belt https://www.amazon.com/BEMONOC-Timing-Belt-Closed-Loop/dp/B07GR3KXK2/ref=sr_1_1?qid=1581574591&refinements=p_89:2GT+Timing+Belt+Closed+Loop&s=industrial&sr=1-1&th=1 Spring for 5mm bolt Custom 6mm thick C-beam gantry plate Custom 6mm thick Motor pivot plate Like I said above, I don't currently have an openbuilds CNC to test it out, but hopefully I can get one soon .
Looks good to me. Bring the belt to the front side of the plate with a stepper standoff mount and you can use a full-width rack for reduced weakness issues around screw holes.
That's true, I could try that. I was trying to have everything fit inside the c-beam but it's not strictly necessary. Actually if I put the timing belt pulley portion on the outside of the plate that would solve several spacing issues, plus I could have a wider spur gear and rack, which would be better force distribution. I'll have to think about that. Might be worth considering for a version 2.
