Optimal build size using 3/4" emt, Carbon fiber PLA in sizes of 4x4, 3x3, 2x2

I have read through so many posts I am getting foggy. I need advice. I am building an MPCNC, at first I wanted to go 4ft x 8 ft, but after getting my build package I see how small the stepper motors really are.

I have been in the world of heavy-duty equipment and construction, so these motors seem very delicate.

Even though I may install say 3/4" stainless steel rod for the supporting structure ($60 each x 4 pieces plus axis’s, $360 later))and using supports where I need it. I get the inkling that my desired size is not of the scope of this hardware. at least not for the long run.

This brings up my question.

What is the optimal footprint ( build size) for these motors?

I know I can use 3/4" Rod etc to take out some of the slop so to speak., use of supports for the structure. I am concerned about the torque on the gantry portion and the span it is attempting. I watch a video of a larger build and it showed a flex that I was concerned about.

Is it reasonable to make a build are of 48" x 48" or should I really consider smaller say 40" x 40", 36" x 36", 30" x 30"?

I recall in the website comments about being 24" x 24", and being able to go larger.

Ah, the joys of a build.

I am hoping someone who has one in operation can comment on the size they are using and how it is going. Did you use Pla or? I am considering Pla with carbon fiber, what do you think?



If you are accustomed to heavy equipment you will need to get used to the idea of some deflection being normal, and this frame of mind may be difficult. Everything deflects and in some cases it can be large enough that you can see it with your eyes.

48" is definitely Lowrider territory. For MPCNC it is a tradeoff between work area and stiffness. There is no hard cutoff but you probably don’t want to go beyond 2 feet of work area unless you have something specific and important in mind and you will be okay with the reduced stiffness. Most important is keeping the Z height small.

3/4" stainless steel rod will probably not fit. Triple check the OD because the MPCNC is made for three sizes only: 23.5mm, 25mm, and 25.4mm. Conduit that is called 3/4" is really nowhere near 3/4" in dimension, it’s 23.5 mm OD. Enough people have made this mistake with 1" conduit expecting it to be 1" OD and then they have pipe they can’t use and 25.4 mm plastic parts that don’t fit any available conduit.

From your mention of industrial equipment (and also casually dropping $360 on pipe), I sense your expectations may be much higher than the cost-conscious hobbyist. I am extrapolating here so I apologize if I’m mischaracterizing. Start small and cheap and see what you are getting into. This is recommended for anyone in fact.

Ordinary PLA will be fine.


I would go with a lowrider if you are going 4x8. The motors are fine actually. I have a smaller, non mpcnc machine that uses the same motors, and I cut aluminum plate at 52 IPM, which is about 23mm/s, so they are enough to get stuff done. The rigidity of the linear motion will bottleneck you before the motors.


My original build was a 4x4, and that was just fine actually. I would be nervous about a 4x8 mpcnc, because of the 8’ spans.


I would say no on the carbon fiber PLA, it doesn’t add much to the strength (at least as far as this application is concerned), since the fibers are not actually connected and interwoven, but still taking up space where plastic should be. Just use regular PLA.


Hope that helps


I wanted to say thank you to all of you that have been taking the time to reply and give me your insights. I hope i didnt give the wrong impression. I am now disabled from a job-related accident working as a Mechanical engineer testing equipment. and looking to do something to be productive and eventually work up to being able to have a shop. But baby steps so to speak.

I agree with all of your thoughts. I have been to Metal supermarket and using a Caliper measured their one-inch tube. The welded tube came in at just over 25.54mm. I was excited at first then realised yes nice to have a larger size but it will rust. Once I clean off the mill oil with acetone. The local store didn’t have any Polished 3/4" tube, They did have a polished 1" but it was larger than 25.75 and it was full of scratched up and down the pipe. So I am back to the 3/4 EMT. I was surprised to see just how thick the walls were with it.

I am going to next focus on the size of the cutting area. I really want to go with a 3 x 4 support, this would give me a cutting area of about 25 x 35. Any thoughts on this size?

My LowRider is 2’x4’, and my MPCNC has a work area of 12"x18"ish.

I comes down to what you are going to use it for. As they pointed out there is no hard cutoff, so maybe if you are wanting to try lasers and drag knives go with an MPCNC, if you are just putting a router on it, at that size, build a LowRider.

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My MPCNC is 24"x 24"
I found that I have approx. a +2mm rise from the edges to the center of the carve area.
The highest point is pretty much the center of my carve area.
I have not actually measured it.

Meaning that X, Y or both rails are slightly warped. Or I need to check the center gantry mount.
But being that it rises from the edges all the way around towards the center, has to be the conduit warp.
Shorter rails (smaller build) may help eliminate this issue.
Or buy new conduit and hope it’s straighter.
Still going to rebuild the center piece and see what that does.

My footing connections are all true to each other as far as height, so, it’s not the side rail levels.
They actually appear to be pretty straight.

Longer means higher chance of this warp issue occurring cause EMT is not designed to be precision straight.

You’ll have to take your chances on slight warps existing with EMT.
Unfortunately you can’t see these with the naked eye.

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My build is 2x4 with a cutting area of around 14x33. I’m really happy with it.

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Finally, I made a few decisions. Here are my choices and thoughts.

I decided to go with a 39" x 48" table with a 2 x 3 work area. This allows for a little room for misc components. This size CNC would allow me to make kitchen cabinets. As most area 22.5" x 34".

The table is made from Kiln dried dough fir 2 x 4, glued and screwed together. Using plenty of 10 x 3" Exterior rated screws. Why exterior? Mainly because I had a surplus of them. I tend to avoid building with nails. I can always reuse screws, from projects I choose to disassemble. Scerws give a superior clamping force and increase friction adhesion to mating surfaces. I used Tite bond III glue. Once the table was built it included a mid-span support in both directions. This should allow for less flex. I had some 1/2" MDO, this was screwed to the supports. The next layer is 3/4" MDF. I cut this sheet to allow for a central area of the working portion 2ft x 4ft to be removable without hindering the supporting area, I can slide a replacement piece right in. The combination of these two has given me a very flat and sturdy surface. Once built I will take a carbide bit and plane the entire surface of the work area to have a parallel / flat surface and be good to go from there. Just for fun, I used a couple of clean pallets for the wood to make a shelf under the table.

I choose to go with the t-track method of hold down instead of a vacuum and pin setup. I decided that the t-track would give superior hold down and ability to hold weird sizes, with various clamps. I will be adding T-track a little later on. Trying to find a good source to buy it.

As for the rails, I am going to see how the 3/4 Emt holds up. I plan to use supports in the mid-span with the supports on the 4ft lengths. This will take care of the stiffness needed over the longer length. Since the flex is mostly on the long side. When I need to do detail or aluminium/ brass, I will keep the work area located to one corner where less flex will be possible.

I also decided to go with a Makita 1.25Hp router, I feel the design will work best. I was close to choosing the smaller Dewalt suggested, but I prefer the Makita brand. Going with the larger router will open up many avenues for me. This also should take a lot of the force away from the rails. as it won’t be struggling to cut through the stock. ( Yes I know to reduce the feed rate)

I choose this Style and brand of a router as having a router that has the strength to cut through just about any material. Even with the size of the 1/4" Collets, the bits are readily available and most likely less prone to snapping during a run. For High detail, I can use an adapter to use 1/8" bits, whereas using the suggested smaller router, the feed rate most likely will be slower using 1/8" diameter bits and doesn’t give the ability to use sturdier 1/4" diameter bits. I also realise the Dewalt DW660 has both 1/8 and 1/4.

The original design of the DW660 is a handheld short cycle use tool. Whereas a router is designed for a longer duration of use. Also, the Makita has the variable speed and a good range of 10,000 to 30,000 RPMS. Since Makita is also a professional brand of tool and tends to have well-made parts. I prefer Japanese made tools over Mexico, China or Taiwan.

We are now printing up the parts needed. This is a great father, Son and Daughter project. We purchased a Prusa to make the parts we need. we figured the cost of the Prusa and the parts to make the MPCNC with supplies is less than some of the name brand CNCs. Now we have two Tools and we get to discover how to build both the Prusa and the MPCNC. Saving money and giving us a great homeschool learning experience.

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The DW660 is not that much different from a router, especially the makita. Both run on brushes, and in fact, my DW660 lasted longer than my makita RT. However, the main reason I would recommend the Makita RT is that it goes down to 10k rpm’s, and can keep it there. Get a collet from elaire that holds better than the stock one, and you can get it in different sizes too.


A note on feedrates, with the bigger bit, you’ll actually go slower, while usually removing more material.

The force will still be transferred to the rails, bigger is not necessarily better (in this case, the makita is not that much bigger anyways)

Lots of the Makita stuff is made in china and mexico, and that particular one is rebranded for several companies. It’s not so simple as “Makita is made in Japan”.

Buy brushes, you may not know how long yours may last, but I highly suggest getting a set to minimize any downtime that may happen.


Try not to get so hung up on the details, get some cuts in, make some projects! That’s the best part.