The Ender-3 V3 Plus is a fantastic printer with one annoying flaw. The filament spool is mounted on the side of the machine, and every time the gantry homes itself, it rises right to the top of the printer and back down again. During this process it pulls filament off the spool and there is an extremely high probability of it springing off the side of the spool as the gantry lowers to the bed, especially if the spool is full. This makes the likelihood of a filament tangle almost inevitable. There was an anti-tangle device included with the printer, but it's fiddly and ineffective.

I have designed this device to clip to the inside of the spool holder as a guide for the filament.

This device stops the filament from falling off the side of the spool when the gantry lowers from the top of the printer to the print bed. Instead, the filament just bunches up between the guide and the runout sensor, but it doesn't tangle.

I consider this a work in progress and I'll post any improvements that I make. So far it has worked flawlessly since I started using it. It's been tested with 20cm and 18cm spools.

If you forget to feed the filament through the hole during loading, there is a little slot that will allow you to do this after the fact.

V2 revision has a slightly longer arm, as the shorter one was getting stuck on the larger cardboard spools.