Taking a page from floppy drives, constrain one side in all axis, the other on one. For the low rider, constrain one side vertically with the wheels and the z axis tubes. Constrain the other side vertically with the rollers but leave it free otherwise. If not, your fighting table wall, carriage assembly parallelism. Least that’s my 3 cents (inflation) and I’m sticking to it, sort of, maybe. Aw heck I don’t know. ~(;<)
Good points. This is really me overthinking things, I know.
For the 3D printer design I’m working on, there are 2 Y axis rails. The one at the low X side is entirely constrained, and is not able to move. The one on the high X side has a little bit of wiggle room +/- maybe 2mm, because I learned from my previous designs about over-constraining parallel rails, and what happens when things heat up. I had assumed with the Primo that when we’re advised not to over-tighten the rails or gantry tubes that this was at least a part of the reason. On my Primo, the side with the drag chain links is tighter, the other would let the tube slide before it would put undue force on the rails. Not that the machine should see 75°C temperature fluctuations like the 3D printer bed, but some leeway should be permissable. It was certainly colder in the basement in December than it is now.
Printed plastic has some give to it as well, so there’s some allowance there, too.
Even when you’re putting in flooring, you leave some room for the floor to expand and contract, which is (part of) what the baseboards are for, to hide the small gap that you leave around the perimeter of the floor.
Well, as I said, when it’s time to build the LR2, I’ll build as recommended, and if there’s a problem, then I’ll address it.
With each motor moving in lockstep, it’s like those guys who weld the differentials in their cars, so that the drive wheels are no longer able to turn at different rates. Those guys go through front tires much faster, because the car doesn’t WANT to turn, since the drive wheels don’t want to allow the left and right sides of the car to go at different speeds. Fine for drag racing, not so good for cornering. Doesn’t help if you twist the frame of the car though! In that case the car will do all sorts of crazy stuff that you really don’t want it to do at 100+ mph.
I’m coming to the conclusion that if I have trouble, then I might consider putting a rail on one side of the LR2 only, and arranging the height to be equal to the original height. If my Primo is any indication, the machine is always going to have lots of chips/sawdust on it, so the wheels will have no trouble sliding a little to adapt to the constraints of a rail.
Of course, I’ll do my best to make the gantry perfect. I’m not sure what the actual lateral forces are on the bit, but they seem to be up to enough to make the core deflect on the Primo. They’re certainly greater than the drag forces on a 3D print nozzle, anyway.
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I’d say that it depends on the accuracy that you’re aiming for. If you’re going to be engraving, or building in wood using epoxy as glue, that’s one thing but if you’re machining precision parts that’s a whole different thing.
For example: my Ender 3’s bed isn’t level by any reasonable standard (it is warped in the middle to at least the width of a printed layer) but using a Z probe mostly fixes the problem. But anything more critical requires me to use my Prusa MK3S.
In this case, I don’t think it is about accuracy standards. At least for me, my LR was very out of whack without them. It would be off track by a cm. Ryan and Barry are not going to let a cm error get into their machines (neither am I) but I was the only one of us that needed the tracks. In a way, that is kind of nice, because being so obvious makes it an easy decision.
Recently completed my LR2 build, it’s also not tracking correctly and is off by 0.5cm in X at about halfway along the Y axis (full size 2400mm build). I’m thinking it might be due to the pull from the vacuum pipe that I’ve crudely tied up to the ceiling with elastic, or that my Y belts are simply not tight enough - both of which I will be playing with to see if it helps… In the meantime, what size C section aluminium did you use to keep the wheels in track - do you have a pic to show? Thanks!
Not C channel, 3/4" angle (L profile)
Thanks for the info and the pic, very clear: using the angles on the inside to keep the wheels ‘pushed out’ and in line. My table is built out of Unistrut so I will drill through it & the L profile and bolt it them together. I feel a trip to the DIY shop coming on… Could I also ask if you have any advice on how tight to tension the Y belts?
Been happy with my modification: pulley wheels instead of skate wheels on EMT tubing is a self-centering, low-friction, and dust-shedding solution. Rails that a skate wheel rubs against will add friction and have some amount of backlash.
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That looks like a very solid solution. I just hope that finding the pulley wheels is easier than sourcing the skateboard wheels was! In some ways this looks very much like the inverse of the v-channel wheels used on a 3D printer. In what way does it shed the dust rather than just compact it - is it just that the dust can’t build up on the round surface?
I got the wheels on Amazon here. I guess I should say it sheds debris and doesn’t allow dust to accumulate beyond a very thin layer. It rides on the very fine edges of the wheels (the center doesn’t make contact), so fine dust is no problem as it cuts right through. Small bits (bigger than fine dust) flung out of the milling operation are more of a concern when running on wheels and the round tube surface does a great job of shedding those off.
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Thank you. We may have different tube standards here in the UK. I can find 20mm and 25mm conduit easily - what size is yours? https://www.screwfix.com/p/deta-round-steel-galvanised-class-4-conduit-tube-25mm-x-3m/7442j
This is very close to my idea for a rail. In my case, 1" DOM tubing is cheaper than conduit because I can get it from work. 3/4" EMT conduit is maybe more convenient, because I can get it at Home Despot.
There isn’t much in the description. I’m guessing these are 40mm in diameter? That puts them a little smaller than the 60mm skate wheels, but the conduit/tube will raise it up more than the 10mm of decreased diameter.
I wonder if I could do this on just one side, and use the skate wheels on the other. The drive mechanism doesn’t really care about the diameter of the wheels matching, and so long as I set up the Z limit switches so that the gantry is level when homed, it should be okay.
The bonus to these pulley wheels is that they don’t ride directly on top, so I could drill through the tube/conduit for mounting screws.
I am UK based and I used this 1” 25.4 mm tube https://www.metals4u.co.uk/materials/mild-steel/mild-steel-tube/cold-drawn-seamless-tube/7413-p there is a cheaper version but I went for this higher specification one. They will cut to length too.
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I think that yours is the most elegant solution: I wish that I had thought of it!
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I have been kicking around all sorts of new LR ideas. It is tough to commit to anything.
I absolutely hate that for some reason some builds don’t track. I have had two builds now, and without much real care put into making sure the side plates are parallel to anything less than a mm mine are dead on. To me this is as big of an issue as people not being able to square a 525 build. Plain and simple design flaw that most builds don’t need it. (people still have issues with the primo but on the order of 90% less). Meaning I built a machine that is too hard to assemble right/well enough.
Belt tension, parallel sides, bolt tension. I feel like we have looked into all of that any never find a smoking gun.
Wheels need significant force to move sideways, I have never ever experienced it. Even with a dirty table. If you ever did add a tiny bit more weight. I just grabbed my LR and slid my table and the wheels did not let go and there is no router in it right now.
The rails should not hit the side of the table if they do that can cause binding.
Now…the caveat here is I start my cuts extremely square. I use layers of tape to get precision hard stops. If you are even a fraction of a mm off, over 8’ you will notice it. The solution for that is simple…endstops. I just never needed them and did not want to add the complication of work coordinates or measuring from home to your workpiece.
The largest issue I have with rails/pipes/guides is your build is only as accurate as you make that one rail. The current design you can have s funky wobbly table and the machine drives in a straight line, even follows a Y axis arc if needed. Meaning you don’t have to be able to build a perfect table, and install a perfect rail. You only need a relatively smooth surface. How do you build a precision table and a straight and level rail without a CNC? For beginners that can be significant enough not to undertake the task.
Not sure what to do with the next LR when the Zen is done.
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To me it sounds as if there is a whole process that surrounds the LR to get it to work properly.
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Thanks for weighing in.
I’m generally a pretty careful builder, but then I imagine so is Jeff. Good to hear about the wheel traction too. I also had all those issues with my first ZenXY, so maybe I’m sometimes not as careful as I like to think.
There are lots of DIY CNC plans out there that start with “Get someone who already has a CNC to cut…” This is why I hadn’t already built something like a Joes 2006 CNC already, it required a CNC to bootstrap it.
Fortunately, I now HAVE a CNC, so I can bootstap it.
For building the table, I built the torsion box that my Primo sits on with a skillsaw, and plywood cut for me at the lumberyard. It would need different support than it has, but I don’t think that I’d have any trouble putting a LR2 on it, it’s straight and square. Way better flatness than I had any right to expect from those warped 1X3 pieces, too. I put it down on the floor, and it wobbled, because it’s flatter than the concrete of my basement floor.
Right now, one of the biggest things holding me back s the cost of lumber. It’s nowhere near as bad in Canada as in the USA, but lumber here has gone through a huge spike in prices too. Production is low, so prices are high. We’re seeing about the same sticker prices here, but of course in Canadian dollars. This is also the big hold-up with the legs for the new Zen table. What I wanted to do turned out to be unreasonably expensive, so I’m looking at a redesign for everything under the table top.
I think that it seems like a matter of build and setup. Once built and configured to work, it seems to continue to do so, but those who have problems… Have problems.
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Thanks for that Jack - I agree they are a very good supplier for the LR parts in the UK, I used them for the X and Z tubes.
I’m using 1", so 25mm should be fine
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You guessed right, full dimensions here:
I’m sure you could do only 1 side. It would be easier in a lot of ways because you wouldn’t have any concerns with keeping 2 rails exactly parallel and would help if the table wasn’t perfectly square. The only issue is that if your tabletop isn’t flat like your rail, then you’ll add some Z variance over the length. Might be easier to match rails to each other than to an existing tabletop.
Yes absolutely. I epoxied mine but was going to do that if the epoxy didn’t hold up.