CORE One hotend fan mesh screen cover

I've had a very bad print failure with some of the spaghetti getting into the hotend fan, causing it to become stuck. Also, with stringy filaments, the very fine wispy hairs would also get into the hotend fan. So I designed this set of fan covers to fully protect the hotend fan from debris and spaghetti.

This should also work with the MK4 but I don't have one to test.

There are two versions:

• A separate stainless steel or nylon mesh screen. I recommend fine stainless steel mesh screen, but nylon should also work. The ones I used are 30 mesh bought from AliExpress.

• Integrated 3D-printed plastic mesh screen.

Both versions have four parts - two each of fan cover and fan cover spacer for the front and back of the fan. The mesh screen is in between the two parts. Note that the fan cover spacer part is not symmetrical, the side facing the fan has a cutout to avoid scraping with the moving fan parts!

Regarding decreased air flow:

I did a quick test with the printer printing ASA at 260 °C nozzle and 55 °C chamber, the heatbreak temperature hovers around 63-64 °C. I then compared the heatbreak temperature with and without the fan cover (with stainless steel mesh), and the difference is less than 1 °C. So the impact in air flow is minimal.

For this reason, I highly recommend you use a commercial mesh screen made from stainless steel or nylon. The 3D-printed ones will have a much higher impact to air flow due to thicker individual strands.

Stainless steel mesh screen version:

• Print two sets of the fan cover.obj and fan cover spacer.obj, with one set being mirrored (you can do this in your slicer software).

• Download Mesh screen cutting guide.pdf and print (with a regular printer :P) at 100% size, you can use a ruler to measure the printed size to make sure it's correct. Note that it's not a perfect octagon.

• Use the cutting guide and a pair of scissors to cut the mesh screen to shape. I recommend taping the mesh screen to the paper.

• Sandwich the piece of mesh screen between the two sets of fan cover and fan cover spacer. Beware of the orientation of the parts! The mesh should be touching the flat side of the fan cover spacer. Optionally use CA glue to secure the mesh screen in place.

3D-printed plastic mesh screen:

• Open fan cover spacer.obj in your slicer, and load modifier.obj as the modifier.

• For the modifier, use 0 layers of perimeters / top / bottom. Then select "grid" infill pattern.

• Print two copies of fan cover spacer.obj and fan cover.obj.

• You can tinker with the infill density and infill extrusion width for an optimal mesh shape.

Try some different settings, feel free to comment with what you've found to work well!

Installation:

Remove the hotend fan by unscrewing the M3 bolts, you don't need to disconnect the wires. Install the two sets of fan covers in the front and back of the fan, orient the protruding tabs on both sets toward the right side of the fan (the side without the M3 bolts). Secure everything together with the M3 bolts.

I also included a model of a nozzle replacement tool re-mixed from the original Prusa design, which fits the fan with the fan covers. They are designed to fit the hotend with the silicone sock.

Print details:

I printed mine with Polymaker ASA. Heat-resistant material is highly recommended since the back cover is touching the hotend heat sink! I recommend 0.10 mm layer height.