Hey Everyone, Working on the Z design for my overbuilt CNC machine and I'm wondering if anyone has information on a good way to attach 'rack' to V-slot? Eventually I want to move my entire machine to Rack and Pinion, but I haven't seen anyone do it yet. McMasterCarr sells pre drilled rack, but I was hopping that someone else has already done the R&D. CNC Mogul is doing it with maker slide but I haven seen any images showing how they attach the rail. If you haven't seen CNC Mogul yet, check it out. Great design, super clean. "Joes CNC Evolution" uses a similar design (rack and pinion) for the X and Y. Also nice! Anyway if you have some info, please share! For now I'll likely just cobble something together so I can start cutting plates, but long term I really like this solution. Super clean and powerful. thanks -Sage
Hi Sage, As I remember reading (somewhere) they were gluing or using epoxy to mount the rack in the slot. Here's a pic of a couple quick mounting ideas for a rack (disregard the plates and pulley, the plate would need to be adjustable with a pinion gear in place of the pulley) that I had worked up a while back. I have not tested the one in the track but it would be cool too Hope this helps
Thanks for the info Mark. Do you know where to source rack that would fit in the channel? Not sure how I feel about gluing the rack in... Hopefully someone will come along that has tried it and tell us how it went. I found a bit more old info here: http://www.buildlog.net/forum/viewtopic.php?f=31&t=1246&hilit=rack http://www.buildlog.net/forum/viewtopic.php?f=16&t=1296&start=10 https://plus.google.com/photos/101440406689536737329/albums/5734777303367817569
Cool looking build I found some rack at mcmaster I think this is the one I have used http://www.mcmaster.com/#6295k12/=px41dm
Check out cncrouterparts way of doing it may give you some ideas http://www.cncrouterparts.com/rack-clamps-p-64.html
Thanks guys. I also found this pre-drilled rack on McMaster, Misumi also has some options for a rack that might fit within the extrusion channel, but is way too tall. Clearly it exists since the CNC Mogul guys are using it, but I haven't found anything smaller than the Misumi stuff. I wonder if they are routing out a channel in the extrusion? http://www.mcmaster.com/#5170t2/=px828u http://us.misumi-ec.com/vona2/detail/110300429830/?Inch=0&CategorySpec=00000029867%3A%3Aa%0900000029871%3A%3A0.8%0900000029874%3A%3A4%0900000029882%3A%3A301.59%0900000029873%3A%3A120 Regardless, I got my v-slot based torsion box and basic CNC frame up and going. Of course now that I have everything together, I'm considering redesigning it... Using 3/4 inch angle iron to reinforce everything is getting heavy and I'm running out of V-wheels. -Sage
The CNC Mogul looks very interesting. I would like to see V-slot have some slide in rack gear option. Would something like the MiniTec toothed rack 8 slide in and snug up with the set screws it has? http://www.minitecframing.com/Products/Linear System LR/Catalog_Pages/28.0051_Toothed_Rack_8.html This would be a great, quick set up option for me. Thanks,
Excellent Mark Hey maybe you could extend the face of the solid v-wheel to be a gear to fit in the rack? Gear drive and guide wheel in one! I'm keep an eye on the Ox build - looks great.
Hey do you have a bug in here! great minds think alike we have boon looking into this but we need to test the delrin gear wear. Its way on the back burner but is an idea worth looking into.
And Delrin wheels are quite economical to change when they wear. So here's where I'm at. I'm totally new to CNC but found this site it V-Slot looks amazing. What a great idea! I want a large portable machine 4' x 4'. Rack and pinion looks to be the best option for me. CNC Mogul is using rack and pinion but with Makerslide. The rack and pinion on the Mogul looks to be some kind of plastic. (Edit - make that metal) new pics on the CNC Mogul web site. I'm OK with gluing in, or 3m VHB tape, the rack gear into the slot, but it can't extend up past to where it interferes with the V-slot Delrin guide wheels. Anybody know of a source for suitable rack gear that is around 5.5 mm width, and less than around 4.3mm in total height to fit into the V-Slot? Pretty much like the CNC Mogul but a little less height? Thanks!
Check these guys out http://www.mcmaster.com/#gear-racks/=q64t8b You could also mount the rack to the back of the V-Slot if you find rack with mounting holes Like in the first pic above
Here is another source of racks. http://www.servocity.com/html/gear_racks.html Check out the site for other parts.
Cool stuff thanks for the link @Frank G Haymes I like the idea of being able to use these racks eaither way with or with out the brackets, dual use.
I second that. Now, if we could use our OX builds to machine toothed v-slot wheel and racks, we could all upgrade to rack+pinion for the price of raw material.
Another: And another: Claim: (updated: all bad rails...) CNCmogul is a trainwreck. Here's what my rails look like: random sized spacers in random positions under pressed in plastic rack. Loads of backlash and binding as pinion travels across high and low spots along rack. Notice how much higher right is than left and neither provide a flat surface for pinion. No amount of pressure will ever seat it properly. No provisions for adjustment of plastic v-wheels to rail or pinion to rack. Tons of resonance coming from all directions, not to mention major deflection at gantry/z-axis, which all ends up where tool meets workpiece. Mine came with junk Chinese controller with counterfeit Toshiba drivers that CNCmogul has refused to replace and I don't see much point in buying another (did get one on amazon, but DOA). Purchased 3 months ago and have been down since day one due to shoddy rails and controller. The new all metal rails look promising, except for hard pinion riding on an aluminum rack. Was promised new machine but it never shipped, I've given up, and am purchasing its replacement from a reputable manufacturer. Lots of successful designs out there with rack and pinion, just expect some noise and vibration. Like CNCmogul mounting the rack under rail or alongside pointed down helps keep debris from surface.
Oh well, CNC Mogul seems to have problems I still like the idea of a removable gantry on the v-slot. I've been searching for racks and can't really find anything cost effective. I have concerns with a belt drive of a rubber band effect. It may not be a real problem, but I'd like a way to minimize it if I use 4ft long rails and it proves to be a problem. I'm back to looking at a hybrid bulldozer drive using belts. It start with the standard belt and pinion as described on this site but with a full belt loop on top. Use a couple of belt pulleys to guide things. I'm looking get get some t-nut bar profile which doesn't seem to be too expensive. Maybe something modified a bit with a lower center section, and tap it in a few places. Put it in the v-slot, tape a GT2 belt on top. It would be like a cheap rack, I think the t-nut bar profile stock would keep things stable. The top belt would mesh to the t-nut slot belt. The glued down belt would keep the belt from too much tension and stretching, in hopes of keeping the rubber band effect down to a minimum. As belts wear they could be changed. If it works, the maybe a modified v-slot extrusion could work. One v-slot could be made shallow so no t-nut bar filler is needed. A belt could be taped directly on the shallow v-slot. This to mesh with a face down belt on top.
If we could purchase 1500 mm V-slot with teeth this would solve the issue. I smell a new part coming soon. Then we could use plastic gears, to stop wear & tear.
This one looks almost perfect Part Number: A 1M12MYHF102000 Flexirack, 1 Module, 2000mm Stock Length, 4mm Face Width. Material- Acetal - Blue. S=10mm, H1=2mm, H=4.3mm, S3=5mm take a look at some of the offerings at Stock drive products (Flexirack).. This may not be exactly what you want but it could be neat to try to slide some gear track into the extrusion slot.. It looks like this one will slide right into the existing extrusion and held captive in the V Slot. http://sdp-si.com/ss/pdf/80501146.pdf
Good find @matt_o_70 we will have to give them a go when they are back in stock. Pretty costly but may be worth it if it works out
Nice ideas people, I too hope to go rack and pinion at some point and like the idea of running rack in a slot, However that would require extending motor spindle, which I would be concerned it may flex. And you lose the option of running parallel sets of wheels, and mine use these on every axis so the rack would need to run under wheels, which if there were a rack that would fit would have to have a very small pitch. My idea is a lot simpler. I plan on simply securing a hardened steel rack at each end so it is floating just above the existing v wheels, but below the motor. I will then add a couple more v wheels under the track on the gantries to support it either side of the pinion, eccentrics could be used here as an easy and accurate way of adjusting how tightly the rack meshes with the pinion. Just need to adapt the y gantry plates and corner brackets to have a support for the rack. And add a couple of v wheels on each gantry. Jobs a goodun, hopefully
Thanks Balu, for bringing this thread to the surface again. All the time I've been on this Forum, I've not seen it before! It certainly gives me ideas to look at rack and pinion. I will go ahead with the normal Belt and Pinion, but hope to use the machine to create plates to take a simple Rack and Pinion system. I may be wrong, but I can't see a problem of screwing a rack along the outside of the V Track on either side. A Nema23 likewise mounted on the outside, with pinion directly driving the carriage. Unless I'm totally missing something. It's dearer than Belt & Pinion, but not that expensive. I know you're very busy Mark, but have you given anymore thought to this system? Jonny. I think we need some pictures for that explanation. Then again, I should do the same. Gray
Too complicated gray, don't think it's a problem pinion running directly without a servo. but if your going down the route of modifying gantries and moving motors, I would seriously be considering getting some linear rails and bearings and sheets of aluminium and building a new machine. I think I still have a cad model of the x gantry in which case I'll make a drawing for you.
Nice and simple. As long as the rack is fastened to a rigid support at each end well enough a rolled steel rack will hold its own weigh laterally. Thats a 15mm high rack, and as you can see still plenty of room to fit a pinion and eccentrics on the additional V wheels to adjust meshing. you may get a little sway back and forth during rapid moves but very much doubt it would be an issue if your pinions teeth are wider than the rack say or moved back slight to allow for it or adding some horizontal wheels would eliminate it. but good quality racks are fairly rigid so cant see it being an issue really.
Still seems feasible, I think. I was thinking, maybe, on the Y axis, 2 pieces of 40x20 slotted ali, joined at each end, with a gap of say 50mm between them. A length of Rack, fixed between them, to the lower face of the top one. The gantry plates would have 3 or 4 wheels on the top ali track, and 3 or 4 wheels squeezing the bottom ali track. The motor, with a Pinion attached, would be fixed on the Gantry plate, with the drive fitting between the 2 ali lengths, and tightened upwards onto the Rack. Do you see what I'm getting at? Obviously I would have to make my own Gantry plates to suit, with my current belt and pinion machine, but that would only happen after I made a few test ones out of MDF or something . Gray
It's is most certainly feasible, and a fixed rail would be neat. The only issue is you would have to figure a way of making fine adjustment to the motor height to get the meshing correct. Why I'm leaning towards using eccentrics under rack.
I'm picturing the motor and all relevant bolts to be sitting in slots of 5mm to 10mm. Now I think it might be relevant as to whether the eccentrics be mounted to the top or the bottom set of wheels? i.e. Should the Gantry be cranked in an upward movement or down? Would this have a bearing on the force applied to the Pinion being forced upward against the track? If you get my drift? Do I even need to consider this? The slots allow the motor to be moved upwards to engage the Rack, then fixing in place. There would be a degree of help from the motor's own weight causing the Pinion to be tilted upward towards the Rack. Although in truth this should make no difference if it is tightened sufficiently. I feel, for some reason, there might be a need to hold the motor shaft and Pinion up against the Rack, additional to the bolts holding the motor. Can't think of a way at the moment. Perhaps the wheels are already doing this? I did see somewhere a Rack which sported holes drilled through the teeth of the rack, at set intervals, which is what I would be looking for. Using spring loaded T nuts to hold the Rack firmly in place. The Pinion would be placed quite close the motor removing any extreme tension of the motors bearings. I see CNC Routerparts http://www.cncrouterparts.com/standard-rack-and-pinion-parts-c-46_39.html do a nice 1320mm Rack for $50. Don't say how wide though. I see they do a R & P Tension Kit. I wonder how that works A nice 10mm wide Rack with a matching Pinion would be what I would really like here. Not quite understanding the relevance of teeth and pitch etc, but just need to give it more though. Gray
