MPCNC new build skr board and wiring

Thanks for the responses. I appreciate the shared perspective. It helps. I’m looking at drag chain vs cable loom with tape measure within and running the wires through the truck tubes for one of each of the x and y motors. I like the idea of the controller on the right side with home on the left and the front clear. Wires will be on the right side and on the back so the front and left will be clear.

What is the best way to route wires for the z axis? Cable drag chain on top of the Y truck tube?
What about router power (using makita). Are there known issues with not separating high and low voltage cables?

One more thing: is the SKR power input on the left side of the board 12V or is there a 5V input? It just says + and -.

The skr board makes its own 5V. You need to make sure you put 12V to the motor section too.

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Is there any danger in using the same 12V power supply for both sections if the amperage rating is high enough?

None whatsoever. Most of us do exactly that.


What is the recommended amperage power supply for this system with an skr and 5 motors? I have a 5 amp and a 32 amp power supply that both supply 12 volts that I can choose between to use. With the display and the processor and 5 motors, would they ever be taking an amp each all at the same time?

The power to the motors gets switched to a needed PWM, so it hardly ever uses the full amperage available to it, and it’s almost never that all 5 motors would be going all out. 5A should be adequate, with all 5 motors set to 900mA. That said, I use a 10A supply for my machine, mostly because i don’t trust the ratings on the Chinese power supplies I have.

As a point of reference, Ryan ships a 6A power supply with his kits. Assuming it is a quality 5A supply, you should be okay. The issue (which Dan points out), is that the rating on some of the cheaper supplies might be overstated.


Chinese 5A or hp 32 amp from a server. I’ll go with the server one. Overkill probably, but it won’t be at 100%.

Is it normal for the skr lcd to show everything mirrored?

Is that a setting that can be changed?

Answer: use 3.27 from Dec 2021 not 3.26 version that is linked in docs

SKR screen is mirrored with touch firmware

TFT35 Display inverted in current Firmware?


The answer is to use github-tomgalleg/tft35-mpcnc or you end up with a mirror or a black and white display, neither of which are super useful.

As a follow-up: it is wired and I tested +X goes to the right and +Y goes away from home at the near left side so it is working in Marlin mode from the LCD. I’ll take base functionality for now as drag chains for the cables are printing.

Is Cat5 ethernet cable unwise for the stepper wires?

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Solid core wiring is unsuitable (Most CAT5 wire spools) for the motor wiring because it doesn’t like repeated flexing, and will fail over time. CAT5 patch cables made from stranded core wiring have been used with reasonable success.

I used some CAT5 solid core wiring in similar projects for point-to-point wiring where it does not need to flex. This could be used for the span where a wire harness stays inside a tube, like going from the X1 motor mount to the X2 in a Primo, but should be avoided for places where the wire is in a drag chain and flexing as the machine moves.

ok I will need to rethink my cabling… Thanks for the input.

Ok, so I have stranded wire, printed some cable drag chains and I’m wondering how is everyone else doing this?

If I put a drag chain on the router mount, how does one connect it to the carriage and what does it mount to on the other side? I see some have put in a channel that rides next to the Y movement bar, but where do they connect on the trucks? I saw a burly system with cable chain mount that used the bearing bolts or maybe the idler bolts as anchor points for the drag chain. That makes sense, but they are facing the wrong direction on the trucks for the primo to be used the same.

How are the rest of you connecting cable chains to the trucks? I’m not really interested in drilling into to side of the truck since they look so nice, but if that is the best option…

It would be good to see what makes sense and what you all have learned about this that isn’t showcased.

I designed a mount for the chain that glues to the truck. I used contact adhesive since I expected to go through several prototypes and wanted to easily remove the bracket, but the first prototype worked well (surprise), and I’ve never had an issue with the adhesive. Attached is a ZIP file containing the mount in both STL and STEP formats. Depending on which trucks you select for the chain, you may need to mirror the part in the slicer before printing. The nut traps are for #6 nuts, and I printed it on its “side” with the dip on the top edge. (38.1 KB)

Thank you for the file! Your printing instructions were clear, so I have it sliced and ready to start. I’m unclear how they mount on the truck though, but perhaps that will become more apparent when I have one in hand to mock up. Thanks again for the quick response! I also just came across this post that has a few other ideas.

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Here is a snap of the bracket mounted. Black on black make it difficult to see, but if you hold the bracket to the truck, the reason for the dip will be clear. Note this bracket was created for this specific cable chain using the spacing of the holes in the mount end. You may have to modify the last link in your cable chain to match the hole spacing, or simply glue the last link to the bracket, or maybe it will be a match.

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it won’t be a match because the drag chain is 3D printed and the connections for it are on the sides of the chain, not an extension at the end, but I can print a new one to match. This will work.

My solution was to use the ends of the tubes, and install plugs in them.

These plugs go into the ends of the gantry tubes. You can see there are openings for the wires to pass through. The holes near the plugs are for rag chain mounts. The box piece top lefta mounts to the core clamp, and holds the drag chain end at the router. This ttaches to the core, so it does not have any pull on the Z tower at all.

You mentioned the z tower pull on the other thread. Thank you for sharing the solution you use.