It’s really easy to over constrain something like a moving bed. It’s better to use 2 bearing posts than 4 on it but they have to be the right capacity. Luckily there is not very much force on it at all, just the drag of the molten plastic, and the weight of the print.
I see why all the printers use the rails at the far end (nothing above them) but they would be better off at the sides. Just like a prusa style gantry moves on the z, swap it with the bed… But all the corexy is in the way. So then it has to get wider, then it gets weaker… Design choices stack up fast.
I have two Z ideas I have no idea if they will be any better, but I do enjoy the testing and designing.
I didn’t actually go into it, 4 have a much higher chance of binding. If your standard z axis is too tilted it will bind. That is one of the main reasons I don’t like auto level, people end up using cockeyed axis. The more rails you add the more perfect it has to be or it will just lock up and skip steps or wear ot the bearings or rails.
Wow, I’m not so sure about this corexy. If anything is even a tiny bit off, the whole thing is way off. Slightly skewed pulleys or idlers and the geometry is far from smooth, the frame needs to be extremely accurate and rigid. Parallelograms and tight belts times two make it even harder to deal with. Quick and dirty does not work for this, so many revisions and just more issues.
I think I might give it one more try but it isn’t looking good for using inexpensive parts. I thought it was just the rails I was using so I switched the 8mm rod and it seems worse.
So it seems to be solved by running a single belt not a double, at least both belts are the same tension, the big issue is when one is unbalanced it pulls like crazy on the frame. This means I might need to reroute the belt, or flip the gantry over, maybe not, ahhhh geometry used to be so easy.
My prototype is embarrassingly rough. I learned a lot for the 5th revision and am working on two different versions now a large one for the Sand table and a printer. I am pretty sure I have most of the XY issues handled, I have not even started on the Z axis but luckily they are completely separate.
Sorry for the slow progress I am a little scatterbrained and working on a few things simultaneously right now that all kind of apply to each other.
This really has my attention as I was looking into making a larger MPCNC just for printing but the 12 in limitation was going to cause me to look else where. If you get this up an running I’d be interest in it for sure. If you have any updates, I’d be interested to hear about your progress and if you’ve moved on to the Z axis yet.
Not yet, just finishing up the ZenXY. I’m not to excited to build another 3D, printer there are so many to chose from. I think I should focus on some other projects first. I can’t recommend the Corexy system yet, especially for larger builds, it is a ton of belt, basically 4x’s your xy dimensions, all hanging in thin air. We shall see if I am wrong about this but my gut says it won’t scale well.
Moebeast, of FliteFestEast MPCNC/needle-cutter fame, has a pretty interesting idea for modest Z-lift capability, suitable for needle-cutter or laser. He’s doing it for a modified LowRider and it incorporates a very compact MPCNC-inspired carriage design… look closely and you’ll recognize the MPCNC Z-axis stepper/pineapple/bearing/leadscrew configuration melded with back to back 4-eared roller assemblies. Check it out
I’m also playing with it and am trying to see if I can retrofit my 2’ x 2’ MPCNC-inspired CoreXY with it… but I’m really afraid all the belts are too much in the way of the Z-lift assembly. I’ve printed the basic carriage body and am going to mock it up on my old camera slider rails (an advantage of repurposing MPCNC parts and retaining the rail spacings) to see what I can see.
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But conduit is so cheap and I’ve got so many MPCNC printed parts laying around that a new machine altogether – built around Moebeast’s carriage design – might be easier than retro-fitting an existing machine . How 'bout a Phlatprinter-inspired, conduit-and-printed-parts CNC design?
