Mpcnc with Linear Bearing

So I just thought I throw this out there.
I was at our CNC tonight at the makerspace I belong to and I was talking about how I really like the kinematics of my MPCNC but I wanted to upgrade my carriage. One thing that’s been mind candy for me lately is that I bought a aluminum casting furnace a few years back and I thought it would be cool to cast a replacement carriage out of aluminum. I’m also have a knee mill for metal machining and I wouldn’t bother me if was going to machine it.
One of my friends pointed out that machining for 606 bearings would take alot of work but if went with recirculating linear bearings that would simplify the process…
After thinking about it bit he does make a good point.

So obviously I would need to highgrade the tube so the emt pipe is out…
I was looking at ali-express and linear bearings don’t seem to be that expensive, although, I don’t know if I could find a hollow ground tube to replace emt.

The thought occurs to me that something like this could potentially be a upgrade to the primo as a 3d printed component, if someone wanted to say with 3d printed components but wanted upgrade.

At this point, my burly carriage is pretty shot after many repairs and I’m wanting a bit more.
Has anyone done anything like this yet?

I was looking at some options for metal parts. Try looking up “lost PLA casting” – the idea is similar to lost wax casting, where you pack a really low infill PLA part in casting sand, (or, it seems, a plaster medium) and pour molten metal (typically aluminum) into the mold to get a cast aluminum part. The molten aluminum melts the PLA and it is forced out of the mold.

One problem that I would forsee is that V1 parts need a little bit of flex in order to adjust to the steel tube. Not much, but some. This is where the adjustments bu tightening bolts comes in, it is expected that the parts will have a little movement possible, and solid aluminum parts might not allow much adjustment.

They would, however, be very rigid.

This would make maximum use of the engineering that has already gone into the MPCNC, and not use the linear bearings.

I don’t know that I would go with the linear bearings myself. This would require hardened steel tube at least. Stainless or mild steel will be worn away by the bearings, which would cause accuracy problems quickly. Ignus Drylin bearings might be OK on stainless, but they also wear quickly and would need regular replacement. Much cheaper than replacing the tube at least.

Even the imexpensive 8mm rod that many 3D printers use is hardened steel, and in sizes like 25mm or 25.4mm are going to be really spendy. It is also typically rod rather than tube, so a rethink of wire management is in order. If you are going to redesign that far, a whole new machine isn’t far off.

First, I guess, find the linear bearings that you want to design around…

I know that there are linear rails that have a solid rod, and linear bearings that ride on it. Could be a good set for X/Y rails, but probably not good for gantry.

I agree with you there that the gantry rails should be hollow to keep the weight down.
I’m sure there’s something out there, but whether it’s a price point, that’s reasonable is another issue.
Time for some googling…

At this point I’d just go with a cnc that’s designed to use linear bearings.

I was in the same boat as you. I love my mpcnc, but no fault of the design, i built it bigger than recommended size. It has 3/4" emt rails, which are fine with small DOCs, but I’ve been pushing it well beyond what should be done. There is a lot of flex mid span with deeper DOC. I will keep mine, but shrink it down to a smaller size. With that being said, I am building a second much bigger gantry style cnc. After examining different linear bearings, they just wouldn’t work well with the current mpcnc design. The new one will be all aluminum 5’x5’ withlinear bearings, ball screws and 450oz Nema 23’s, external drivers 48volt. To save shop floor space, it will also be vertical (15-20 degree from vertical). This is similar design to one we have at work, so have a working model to reference. Using the same control board as my mpcnc. All said and done will still be much cheaper than some of the systems out there (although the aluminum was free). So, you’re not the only one. Still tip my hat to Ryan every time my mpcnc makes chips, awesome machine as designed!!!

So, was doing a bit more googling and noodling a I just couldn’t see a easy economic way to do MPCNC type X-Y rails using linear recirculating bearing. That did however got me looking at the problem from different angles… I have some 1" square tubing that i think could make a very nice set of X-Y rails and I happen to have a schneeberger cross bearing slide assembly in stock which could may a over-designed z -axis assembly. Most of the stuff that I’ve seen on youtube, sucks up a bunch of restate but I think, but I think I found a solution that I haven’t run across that is quite compact and I think super rigit… I haven’t seen anything quite like it. It’s going required a bit of machining, but if it works should be pretty cool.

I layed it out in 2d in freecad, and I need to teach myself the Assembly 4 work bench in freecad to see if this works. Parts are on order.

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