MPCNC + Printer with two Arduinos

Hey everybody

I’m using a MPCNC with ramps 1.4, but my 3D Printer broke down lately. So I was planing to do both Milling and Printing on my machine. I was wondering if it’d be possible to install two arduinos and ramps to the same Motors (everything but extruder). I’d build a switch to power only one of the ramps and would have two separate usb cables. My hope is to keep homing/autosquare on the mill and manually home one axis on the printer. Since my controller is quite cramped away, I think it would be easier to just change the setup(heated bed+hotend+extruder) flick the switch and use the printer usb cable instead of rewireing the ramps board. But the Stepper cables would be connected to 2 Stepper drivers at all time, even though just one is running. Same for the not duplicated axis endstops.
I hope I described my idea sufficient enough :worried: :slight_smile:
Thanks for the help!

I have not seen that configuration before. I am pretty sure having one set of drivers connected to another would be bad.

A board with 6 drivers (or a ramps with a 6th board added) would work. You would leave the hot end connected when milling, so you would not get temperature warnings. There isn’t any 3d printing and dual endstop firmware configured, but it would be possible.

If you are connecting to a computer all the time anyway, reflashing the arduino would be pretty simple. (Xloader makes that much easier). But you would have to swap out motor cables, at least. Because E0 is either an extruder or X1 depending in the firmware.

A board like the skr pro can handle 5 motors and an extruder. There isn’t a firmware configured for that, but it would be close to the dual firmware, but with extruders set back to 1. You would again leave the extruder connected all the time when milling to avoid errors

Thank you for the answer Jeff, you helped me a few times already :kissing:

I thought so swell, two stepper drivers sound like a lot of possibilities for errors. I’m doing enough of those myself, no need to multiply those :laughing:

If I stick to one board only, I’d think about an BTT Octopus. So future advances like a 4th axis would be a problem aswell. Any thoughts about this board?

I try not to keep up with all the new boards. Otherwise, I would spend all my money on replacing perfectly good boards.

We have pretty good setups for the skr pro, rambo. Other boards are possible, but you need to dive into the configuration on your own.

You’ll be diving in regardless, if you are doing this kind of hybrid machine.

The other thing I should say is that the MPCNC is capable of 3D printing, but there are a lot of cheap printers out now. Keeping them as separate machines has a lot of benefits. If you are interested in a project, this could be it. But if you want two tools, then it would be a lot easier and possibly cheaper to make them separate.

Thanks for the insight, if I go the octopus hybrid route I’ll keep you updated!

Found out about Stepper Expander Boards. These seem to be the cheapest option and instead of changing to marlin I can keep grbl with working macros and just need to switch the limit signal pins for X2/Y2 (A/B) to some free pins. For now I will try this…

But big thanks to you @jeffeb3 for always reaching out and trying to help where possible!

1 Like

In the end I just ordered a new 3D Printer…


I’m late to the party, and you already went with a new printer. However, I did exactly this with my MPCNC. That said, while it’s wired up and working, I never actually used the 2nd board for its intended purpose haha.

What I did was use a series of 4-pole mechanical DC relays. Each pole has normally open and normally closed contacts. So, I wired normally closed to one board, normally open to the other board, and the common to the device (Stepper/limit switch). Worked out neatly as each stepper is 4 wires. Then I had a switch that powered the relays on/off and that switched the contacts between the boards. It took up a bunch of room and double the wiring, but was a pretty clean and simple solution.


Sounds awesome! I found those relays a few days after ordering the printer, but in the end I’m happy to have two machines. The cnc process is developing so much dust that it seems impossible to get the machine into an “as good as new” state. All this dust would drop down onto the printbed or onto the layers, making bed and layer adhesion quite a problem I imagine.
Since I designed and build a drop in Hotend for my makita holder already and am on the way to establish a 6th stepper for the 4th axis I will keep the ability to print on my MPCNC and just flash a new software and connect the extruder instead of the A-axis. No heated bed though (yet). I’ll keep you posted if the time comes…