Whiteboard eraser on magnets, velcro and felt

31.05.2025. update.
The 48 x 18 x 2,5 mm has stronger magnetism since the area of the magnet is larger.
I made the magnet section larger since I noticed even the same brand of 3D printers even with the same settings have different print results. Creality Ender 3 would print the cutouts rather narrowly, and you would need to use a construction knife to widen the cutout while good old Ender Max would make those just right. I added 1 mm extra just in case.

Components:
■ NdFeB magnets 50 x 18 x 2.6 (in reality those are 48 mm) - Temu or AliExpress (not sharing links since listings change).
■ Self-adhesive velcro 50 mm wide - I took 5 meters - Temu or AliExpress
■ Gel superglue for gluing magnets to the eraser body your local DIY shop
■ Felt material from known brands. I used Bi-office or Esselte. There are options for buying sheets and cutting those out, but that is a bit tricky since the sheets are soft and stretchy. The felt cutouts might become uneven.

PS. Attaching also both f3d and STEP formats since magnet sizes are inconsistent on Ali or Temu. Today 50x20 mm is available, tomorrow it is completely gone, and you are left with 40x20 mm or 50x10 mm sizes. You would need to modify sketch called "bottom_cutouts" for magnets. If base needs to be narrowed down, just mod the sketch called "base".

April 2025. Do 10% infill. As testing on multiple boards at my school has shown, the more expensive and quality boards have a thick metal backing under the laminated white sheet and stick and hold well. Cheaper whiteboards have thin backing and thus the magnetic force is weak. The solution is to reduce the infill from 20% to 15% as it will improve magnetic hold. I also printed 10-12% and it works well as well.

Reason for make. Our school got tired of paying 8+ Eur for erasers that fall and break, so I designed my own. In terms of expense per 1 Eraser it would total around 3,7 Eur. Will do the exact estimates later.