Z-axis cat ears for MK3 and MK4 series printers

Introduction

Is your printer missing a certain amount of cuteness or nyaa? I felt that mine was, so I designed some cat ears designed to perch atop its Z axis. Now, you can have nekomimi for your printer too!

This is designed to fit the MK3S+ frame, which means it should also work for the MK4, but I haven't verified it.

What you will need

There are two versions of the design: one using heatset inserts, the other using M3 square nuts. Whichever you choose, you will need a left and right version of the appropriate design printed: for example, if you want to use heatset inserts, you want to print ‘Z-axis-cat-ear-heatset-left’ and ‘Z-axis-cat-ear-heatset-right’.

Regardless of whether you chose heatset inserts or square nuts, you will also need four M3x15mm socket head cap screws (the same kind used to assemble the printer). These will replace the four screws that attach the Z-axis tops to the frame.

If you decided on heatset inserts, you will need four M3 heatset inserts. The design is intended for diameter 4.6, length 4 (M3, D4.6, L4) inserts. You can use a wider diameter, but if you do, you may have to remove some excess plastic. You can also use a shorter length. Narrower diameter inserts likely won't seat properly, while longer length inserts will poke out.

If you decided on square nuts, you will need four M3 square nuts. These are also used to assemble the printer, so you may have some spares.

How to print

The parts are designed for a 0.4mm nozzle, 0.2mm layer height, and 3 perimeters at 0.4mm extrusion width (that is, 1.2mm walls), as well as 1.2mm thickness on both top and bottom (6 layers for both top and bottom). As the part is not load-bearing, you can use as much infill as you like, and can use 2 perimeters if you prefer. This should be printable with a 0.6mm nozzle, but I haven't tried it. Supports should not be necessary: if you have trouble printing the overhang, try a thinner layer height. Layer heights thicker than 0.2mm are not recommended.

If you don't plan to enclose your printer, you can use any material you like. If you plan to enclose, I don't recommend PLA or PETG: enclosure temperatures can soften and deform PLA, and PETG is prone to warm creep, which can cause screw loosening. Instead, I recommend ABS (or ASA) in such cases.

How to assemble

Important: Read all the instructions first, then follow them in order. These assume an MK3S+: the MK4 will be quite similar.

1. Insert either the square nuts or the heatsets into the provided holes, depending on which you chose. For heatsets, it's easier to insert them from the ‘top’ side (next to the ceiling and buttresses) instead of the ‘bottom’ side (which will rest against the frame).
2. If your Z axis is already assembled, undo the outer screw connecting the right-hand Z-axis top to the frame completely, and remove it. Otherwise, skip to step 7.
3. Insert one of the M3x15mm screws into the hole created by step 2, and tighten it until it goes through the Z-axis top and the frame, and pokes out a tiny bit. 
4. Use the slightly-protuding screw from step 3 to align the outer mounting hole on the right-hand ear. Then tighten fully.
5. Repeat steps 2 through 4 for the inner screw.
6. Repeat steps 2 through 5 for the left-hand Z-axis top and left-hand ear. Then, you're done! Ignore all other steps.
7. If your Z axis is not yet assembled, follow the Z-axis assembly steps up to step 9. Then, during step 9, instead of using M3x10mm screws, use M3x15mm ones. Screw them in only until they go through the Z-axis tops, and the frame, and poke out a little bit.
8. Use the slightly-protruding screws from step 7, align the mounting holes on one ear (doesn't matter which one), then tighten fully.
9. Repeat step 8 for the other ear. Then, you're done! Ignore all other steps.

The files

I've provided both STL and STEP files, as well as the original FreeCAD project used to make this design (as per the license). You can find them sorted into folders.