Let's say I want to build a mondo machine

First: Apologies for the wrong terminology, if there is any.

I built one MPCNC already, the cutting area is 30cm by 30cm, and while I thought this would be plenty at the time, it has dawned on me that anything serious will require significantly more surface area.

So: My question is how large could I actually build this? I have access to 25 mm OD stainless steel tubing with a wall thickness of 1.5mm.

I would optimally want something like 1m by 2m cutting area, I am aware this would be slow, I am not concerned with speed (or really pinpoint accuracy either, just as long as it doesn’t flex more than a millimeter or two, besides, as I understand it, a finishing pass will give me a large amount of additional accuracy even with a large machine). I have a welder. I was thinking I’d weld a length of flat bar on the bottoms of the outer tubes, and do the trick someone mentioned with adding the square stock to the tubes that cross each other. I also have a rather high Z travel, 80 mm or so, I wouldn’t actually need this much I don’t think if this would be problematic. The machine would be used mostly for cutting plywood, some plastics as well as some regular old wood (no MDF as the owner of the space I’m housing the machine in is very adamant I not use said material due to past experiences).

Before you suggest the lowrider, I have to tell you I have no access to 25.4 mm OD tubing, and as far as I can see, there are no CAD files available for the parts, and using meshmixer or something else like it to modify the meshes directly isn’t really an option.

If you can wait a bit, the updates for the lowrider include a 25mm option.

If you want to go big your way, make the Z as short as possible, one midspan support on each long rail, and give it a shot. Worst case you spent money of a bit of conduit and some belt, you can always go back.

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