Revised Core One door magnet holder

Found the door of my Core One wasn't being held as firmly as I would like - especially after screwing on the handle instead of using the sticky pad.

The magnet holder was remade in FreeCAD 1.0.1 basing the new design on the original magnet-holder-r1.stl from the Printable Parts package.

It holds the magnet closer to the door - no longer flush with the frame, but the door sticks more securely. I also added a small hole opposite the slot, so the magnet can easily be pushed out of the holder with a paperclip wire.

I printed using ABS for temperature stability - but PETG should be fine, too. 

Attaches to the printer in the same way as the original - but the magnet sticks through the hole to about the same height as the button head screw. The door sensor switch should work fine.