A list of questions as long as a gorillas arm!

To start, I just found the MPCNC for the first time last weekend and I immediately started printing parts!! I haven’t been this excited about a project in a long time!! I got into 3d printing and laser engraving a few years ago and now all I can think about is building a Primo, first for a CNC mill and then after that I want to build a larger format 3D printer. Here are my questions (please bear with me if my questions are off point or reflect a degree of understanding):

  1. I’m not averse to buying a controller like the SKR Pro V1 but the DIY part of me wants to build it. I can find parts kits on AliExpress to build a Arduino/RAMPs controller with a display.
  • Are A4988 stepper drivers sufficient to operate the NEMA 17’s?
  • If I go this route, is it capable of running Marlin or GRBL? I think because my next project is going to be a bigger 3D printer maybe I should focus my studies on Marlin.
  • I currently use Lightburn with my diode laser. If I build a controller with the parts I mentioned earlier and use something like Universal GCode Sender, would this be a similar experience? i.e. Connect my laptop to the Arduino via a USB cable and send the GCODE that way. What if wanted to simply drop a the file on an SD card to take out the garage to use it? Is there a provision for that available?
  1. In the build documentation on the on the calculator page there’s the statement “For a Primo MPCNC, 81mm is the shortest and I highly recommend that.”
    Does that mean no more or no less?
    81mm seems vertically limited if I wanted to build one as 3D printer?

  2. I was thinking of going with 31.5" by 31.5" for XY. Too much for a first build?

Thank you for any guidance that you can provide to total noob.

Super thank you to V1 Engineering, I haven’t felt this giddy about a project in ages!!!


You can build it with ramps. The Rambos and the skr pro were chosen because they are easier to use and harder to break. The ramps and mega clones work, but they have really cheap parts in them. Ryan used to sell the ramps and he had to stop because so many were failing in his initial tests. But there are a lot of successful ramps builds. There is preconfigured firmware for ramps at MarlinBuilder releases. It expects drv8825s, but you can use it as is, or fix the two or so places where it matters. The steps per mm will be wrong, but that can be fixed with gcode.

UGS doesn’t work with Marlin, AFAIK. Cncjs, repetier host, octoprint, all work that way. More info here: Software Workflow - V1 Engineering Documentation

That is the recommendation for a mill/router. The current advise is to not use the MPCNC as a printer. You can, but there is a lot of moving mass. Newer printers are cheaper and faster for the same build sizes.

It would work. But if you really want that size, the low rider 3 is going to work a lot better at that size.


I currently use Lightburn with my diode laser…

You can connect Lightburn directly to a Marlin machine, or you can write the g-code to a file and deliver it using any g-code sender, or you can run the job from an SD card. Personally, with Lightburn, I save my jobs to an SD card since I don’t like having my laptop in the shop area.

For a Primo MPCNC, 81mm…

The issue is how far the tip of the router bit is below the core when cutting. Greater distances mean greater leverage and therefore more potential deflection. There are ways to have a tall machine while also mitigating the impact. You can 1) have a drop table that lowers/raises the working area, or 2) have multiple different heights of the spoil board that lifts shorter work towards the core, or 3) have adjustable legs. Personally, I occasionally do cosplay props for my daughter using 2" foam, so I made my machine with adjustable legs. My Primo spends most of its time with only 80mm of working height, but I can adjust the working height upward when cutting foam.

  1. I was thinking of going with 31.5" by 31.5" for XY. Too much for a first build?

If your measurements are for working area (not machine size), then this size is on the bigish side for a Primo. There are Primos and Burlys this size and bigger, but you do pay a penalty. You might want to have an initial experience of a Primo of a somewhat smaller size…or consider a Lowrider.

  • Are A4988 stepper drivers sufficient to operate the NEMA 17’s?

A4988s will work fine, but, reiterating Jeff’s info, the V1 maintained firmware for the Ramps 1.4 board is configured for DRV8825 drivers. If you go with DRV8825 instead of the A4988 drivers, then you can use the V1 maintained firmware without changes (assuming the same display). You would not even need to compile the firmware. You can transfer the provided binary using XLoader.

running Marlin or GRBL…

Most V1/MPCNC machines run Marlin, though GRBL seems to be making some inroads. Typically, boards will be either Marlin or GRBL, though there are a few boards that will run both. You will get more support from the forum if you use Marlin.


Hi Robert & Jeff,

Thanks so much for the great advice, I have a 5 pack 8825’s on the way!

Also, that “Software Workflow” article was really good for demystifying the process.

Lastly, I’m going to downsize the workspace to 710x710x81mm.

Well, you probably won’t hear from me again for a week or so, or at least until I get the rest of the pieces printed and the unit assembled. I started with the core, so the biggest piece is finished anyway.

Huge appreciation for your help on this!!


I have ramps with 8825s. The only problem i have had is the lack of backfeed protection. I was in a hurry one day and manually moved the machine too fast. It caused a burnout on my board. But ramps boards are cheap and i already have a new one. just need to replace it.

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Is there any kind of backfeed prevention devices on the market? I could see myself doing that same thing!

Welcome to the fun club!! Enjoy the ride. I’ve been here for a few years now, and I still get giddy over new knowledge, experience and outcomes.

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No that is why others are much more expensive.

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Just don’t push it that fast when it is unpowered. If your screen lights up, don’t go any faster.

If you have to drag it with you in your car and you are worried about it, unplug the motors.

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