MPCNC Primo - Would this setup work?

I’ve printed all of the parts for the Primo and have been really excited about it, but now am starting to worry that I chose wrong and need to build a Lowrider instead.

Originally wanted a 24’‘x24’’ work area but then decided that 24"x30" or 24"x36" would better fit my needs.

If I’m using 1" DOM, would this workspace be doable or am I looking at a lot of flex/chatter?

Thanks all for any advice that you can provide!

Depends on what you consider ‘work’. There would be flex and chatter, but with light enough cuts, it would work. It would work better towards the edges of the machine and would have more flex in the middle.

I would recommend a LR3 for the large work area, though.

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Thanks for the feedback. That’s what I was worried about.

I think at this point I’d rather be in for some extra print time and filament than to do something I’m unsure of or would wish I’d done differently later on.

Have you considered building the MPCNC at 24"x24"? There is a lot to learn on CNC. If you get it going, learn through doing several projects, then you will know enough to be confident in building a LR3, or keeping your primo. Things like the electronics can come with you to the new machine. Maybe some of the tubing. But not much else. So it wouldn’t be a complete waste to build it as-is. You can also use the mpcnc to cut the flat parts for the LR3.

I can easily say that from here. Because I don’t have to spend any more on new tubing, hardware, or prints. But that is what I would recommend.


I’m a real big fan of the lr3 at any size, but I’m with Jeff anyway. If you’ve already got the parts and the plan, roll with it. You can tile the occasional large job that you want an extra 12" for.

The LR3 brings with it the extra cost of linear rails and the added complexity of partially assembling it, cutting cutting some parts, then diassembling and reassembling with the new parts. Also involves some flat pieces in addition to the printed ones, vs all printed parts on the primo.

Both machines are great, you won’t regret building either one, you’ll almost certainly wish you’d built whichever one you don’t build (and will probably build it next, anyway), and you’re gonna have a blast.

The primo is just a more direct start from where you are.

All good advice here. Some extra from a guy with 2 oversize Primo’s.

On the DOM tubing, there is 2 standard wall thicknesses, 0.095" and 0.120". I used the 0.120" thickness.

On cuts, feed and speed make a difference on flex and accuracy, no matter what the build/tube/model of machine. I can do 1/8"-3/16" or so at above normal speeds with less than 0.001 flex at the center on the big build, which has a 42" X, and a 20" Y. Alternatively there are existing center span supports on Thingiverse to dampen down flex, I haven’t tried them though.
The Z lead screw can put a lot of force on the bit, that is why it can flex on the X and Y rails

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