After converting a Prusa Mk4S to a Core One, a maker found the default side spool position became inaccessible. The workaround turned into an over-engineered top-mounted spool holder: a stackable box with a front lid, a sliding rail, and a magnet-attached hold
For FDM printers, loading filament sounds simple—until you have to decide where the spool goes.
On “bed slingers,” spool holders are often top-mounted. On enclosed CoreXY machines, that hardware can end up on the sides, on the top, or—at least according to one maker—on the back. And if the side option blocks access, the machine’s convenience can evaporate fast.
That’s the problem that pushed [3D Maker Noob] to build a top-mounted spool holder that goes beyond typical add-ons. The project started after converting a Prusa Mk4S to a Core One using the conversion kit. which changes the position of the spool. Suddenly. the maker had to work around not having access to the right side of the machine where the default position is.
His first attempt used many left-over parts from the original Mk4S to create a box-shaped spool holder. Then he went further. In a video, he documents the upgrade, and the project files and instructions are available on Printables.
The finished result is a flatter, multi-spool-like box that stacks on top of the printer. There’s a flippy lid on the front, and when it opens, a rail slides out. The spool holder attaches magnetically to that rail, and the holder can be customized to fit different spools.
Even with all the extra engineering, the core payoff is hard to miss: it fits in confined spaces and looks polished while doing its job. In a setup where the side position won’t work, the design effectively turns the spool problem into something controllable again.
Prusa Mk4S Core One conversion kit CoreXY FDM printing 3D printing spool holder Printables magnetically attached spool holder maker project
So basically the conversion kit broke the spool access and he had to build a whole contraption? lol
I don’t even get why they moved the spool position “suddenly” like that. Seems like a design flaw from the start. Also top-mounted spool holders always feel sketchy to me.
Wait is this the printer that’s like… CoreXY but it ends up on the back side? I swear I saw someone say you can just use the original Prusa holder and route the filament through a different path. But I guess magnets are cool? Idk
Man people really take one inconvenience and turn it into a whole engineering project. “Flippy lid” and “sliding rail” is kinda extra, but I’m not against it. Printables folks always come through, though half the time I can’t tell if it’s for enclosed machines or not.