Sunlu S4 anti-tilt spool cradle

Two nights in a row, I woke up to my printer printing in mid-air 😪 Both times, the cause was a near-empty spool tilting on the Sunlu S4 rollers, causing a tangle up against one side of the spool.

Here is my solution: a 2-piece cradle that stabilises a standard 1kg spool both side-to-side (with wider roller spacing) and front-to-back. There are 2 main versions:

1. With guide rails for spools up to 68mm wide (Polymaker, Bambu, eSun)
2. Without guide rails for thicker spools up to 77mm (Prusament)

The cradle consists of 2 identical halves, so you need to print 2 to make 1 cradle. Recommend 0.20-0.25mm layer height, with 2-3 perimeters, no supports. There are 2 versions with different size holes for the roller bearings, 12.1mm was a perfectly snug fit for me, but if that's too tight, there's also a 12.2mm version.

Filament Choice

Due to the heat inside the S4, an appropriately heat-resistant filament must be used to print these cradles. For 55C and under I find PETG to be sufficient, any higher and you would want to look at ASA, PC, or some fibre-reinforced material.

Assembly

1. Pull the 2 rollers out of the bay you want to upgrade
2. On a flat surface, push the rollers into one of the cradle halves until they bottom out
3. Invert the assembly and push the other ends into the other half
4. Secure the cradle legs together with 2x M4/M5 machine screws (10mm thread) and 2x M4/M5 nuts
   1. If you don't have 10mm screws, you can insert an M4/M5 hex bolt up from the bottom, and tighten a nut on top instead