K2 Build Log Part Nine: Backpack

Apr 6, 2022

Take a look at the eDrawing to see where everything goes inside the backpack.


Let’s get all the mounts attached first.

UHP power supply

Insert 1x M3 tall heatset insert into each mount as shown below

First heatset insert installed into uhp mounts

Hold your power supply next to a mount to figure out which of the two adjacent holes the second heatset insert needs to go into.

Figuring out hole for second uhp mount heatset insert

Put the heatset insert into the correct second hole.

Second heatset insert installed into uhp mount

Use 4x M3x10 SHCS to attach both mounts to the power supply. Mind the orientation of the power supply, I oriented mine such that the input was on the left and output on the right with mounts pointing up. I originally had it oriented with the input on the right and fixed it later, so don’t get confused if the orientation looks different in later pictures.

Mounts attached to the power supply

Bolt the mounts to a backpack extrusion using 2x M5x10 BHCS on the top

Mounts attached to the extrusion at the top

and two on the side

Mounts attached to the extrusion at the side

RS power supply

Attach the mounts to the power supply using 2x M3x8 SHCS.

Mounts attached to RS power supply

Attach the mounts to the extrusion using 2x M5x10 BHCS on the top

Mounts attached to the extrusion at the top

and two on the side

Mounts attached to the extrusion at the side


Attach the SSR to the extrusion using 2x M3x8 SHCS. Mind the orientation.

SSR attached to the extrusion


Let’s prepare the WAGO mounts. Place the WAGO mount in place

WAGO mount placed in the slot in the 24V mount

And slide it in. It should click into place.

WAGO mounts slid into the slots in the 24V mount

Repeat for the other WAGO in this mount and the WAGOs in the other mount.

WAGO mounts slid into the slots in the 120V mount

Attach the 24V WAGO mount to the extrusion using 2x M5x10 BHCS.

24V WAGO mount attached to the extrusion

Attach the 120V WAGO mount to the extrusion using 2x M5x10 BHCS.

120V WAGO mount attached to the extrusion

Raspberry Pi

The controller mounts are assembled identical to the Raspberry Pi mounts, so I’ll explain it here and not repeat the instructions for the other controllers.

Note - Specifically for the Pi mount, you might have to shave a bit off of the corner in the picture below. On my Raspberry Pi 3B+, that corner overlapped with one of the components soldered to the board. You’ll find out whether you need to shave yours once you’ve assembled both mounts and aligned your Pi on them.

Corner shaved off one of the accent pieces

Place the accent pieces on the slots.

Mount accent pieces placed in place on the mounts

Twist the accent pieces, they’ll get locked into the slot and can be slid back and forth in the slot.

Mount accent pieces twisted in their slots

Place the top half of the heatsink onto the Pi, place the Pi on top of the mounts, and bolt it in using 4x M2.5x16 SHCS.

Pi attached to the mounts

Attach the Pi mounts to the extrusion. You’ll have to use a long hex driver and a lot of patience. I don’t have pictures of this because I attached mine after mounting the extrusion to the back panel.


Insert 2x Tall M3 inserts into the main mounts, and 2x Tall M3 inserts into the accent pieces.

Heatset inserts in the controller mounts

Insert the accent pieces and twist as before.

Accent pieces inserted into controller mounts

Slide the accent pieces to the ends of their slots and attach the controller to the accent pieces using 2x M3x8 SHCS. Attach the mounts to the extrusion using 2x M5x8 BHCS.

Controller attached to extrusion for alignment

Slide the controller up and into place, and attach it to the main pieces using 2x M3x8 SHCS.

Controller completely attached to the extrusion

Repeat this process for the expander board. Insert your USB cable into the main controller to make sure that you leave enough room between it and the expander board.

Controller and expander attached to the extrusion with enough space between them


Insert 6x M5 heatset inserts into these holes:

M5 heatset inserts for backpack corners

Insert 1x M3 tall heatset insert into the remaining hole:

M3 heatset inserts for backpack corners

Attach the corners to the back panel with 2x M5x10 BHCS each.

Backpack corners attached to back panel

Installing the back panel

Note I did this backwards during my build and attached the electronics-mounting extrusions to the panel before attaching the panel to the printer, so the following pictures will have the extrusions already installed. Just ignore that part and focus on the panel. I thought about the entire process while I was writing this build log, and I believe that you’ll have an easier time if you install the panel first, so that’s how I’m structuring this post.

I wanted my back panel to be held in using roll-in nuts, but starting off the installation with roll-ins is hard because it’s a heavy panel, and holding it in place with one hand while adjusting roll-ins with the other is cumbersome. I recommend you start with hammer head nuts, and then - if desired - you can switch to roll-ins later, once the panel is partially attached to the frame.

Close up of a hammer head nut

Place spacers along the top and bottom sides and insert 4x M5x10 BHCS bolts through the panel and spacers into hammer head nuts. If you plan to use hammer heads long term for the back panel (as opposed to switching them out with roll-ins) then put the side spacers as well as all required bolts at this stage.

Back panel with top and bottom spacers held together with hammer head nuts and M5 bolts

Insert the nut side of the panel into the back face of your printer, secure the top and bottom sides by tightening the bolts. Start inserting roll-in nuts into the left and right vertical extrusions and position them by gently flexing the back panel. You won’t be able to roll them past the through holes made into the extrusions at gantry height, so the lower ones will have to be inserted at the bottom of the printer.

Positioning roll-in nuts for side extrusions by flexing the back panel

Insert the spacers and use M5x10 BHCS to secure the sides, and then you can remove the top and bottom bolts and nuts, place roll-ins in and replace the bolts. Positioning the roll-ins is similar to the previous step, you’ll have to gently flex the panel.

Positioning roll-in nuts for top and bottom extrusions by flexing the back panel

Installing the extrusions

Note - Ignore the square black printed pieces you see on my panels in the following pictures. The backpanel DXF changed after I’d placed an order for my panels, so mine came with holes that overlap with motor locations. I drilled holes at the right locations, and printed pieces to plug the faulty holes, those printed pieces are what you’ll see in my pictures.

I recommend using hammer head nuts instead of roll-ins for this. You’ll have a really hard time positioning roll-ins correctly. Insert 4x M5x8 BHCS (eDrawing says M5x10 while I’m writing this, and it’s incorrect) through the back panel and lightly screw hammer head nuts onto them.

Bolts and hammer head nuts through back panel

Slide one of the electronics-mounting extrusions onto the nuts.

First electronics extrusion attached to back panel

Position it so that the ends don’t stick past the corners. Tighten the bolts.

Close up of one end of the just-installed extrusion

Install the second one in an identical fashion.

Second electronics extrusion attached to back panel

Your panel should already be on the frame if you followed my advice and did that first. If you didn’t, go follow the advice in the last section to install your panel.

Backpack attached to back panel


Insert the grommets into the back panel. The hex side should be inside the backpack

Grommets inserted into the back panel

Screw in the other halves of the grommets

Other halves screwed onto grommets

Power inlet

Insert 2x M3 tall heatset inserts into the printed part.

Heatset inserts installed into power panel

Insert the power inlet and rocker switch into the panel.

Power inlet and rocker switch inserted into the panel, rear view

Use 2x M3 tapping screws to attach the plug to the panel. Pop the fuse holder out, I used a flat head screw driver to lever it out.

Fuse holder removed from the power inlet

Put two fuses into the fuse holder and pop it back into the power inlet.

Fuse holder with fuses inserted

Blanking plates

By default, the side panel with the power inlet has two blanking plates. You can substitute either with a plate of your choice. I substituted one with a plate that has space for an hour counter, a keystone jack and a bowden inlet. It’s this mod with some added holes so that I can screw the hour counter in. Insert 4x M3 Tall heatset inserts into each plate

Heatset inserts installed into electronics blanking plates

Populate the plate(s) if applicable

Hour counter and keystone jack inserted into blanking plate

Installing the side panels

Attach the power inlet plate and blanking plates to the laser cut side panel piece using 4x M3x10 SHCS each on the inside, then attach the panel to the corners using 4x M5x10 BHCS.

Side panel with power inlet installed on backpack

Should you choose to, you can also install the other three side panels at this time. However, I recommend doing that after you’re done with wiring. I broke a chunk out of one of my side panels by accidentally smacking it with wire strippers.

Other side panels installed on back