Step 3: Making the Key
What we're aiming for. The split ring attaches to the back and the magnet to the side of the key, they're held on by a glob of shapelock that makes the new key handle.
By using a neodymium magnet with a countersink hole, a conical plug of shapelock in the hole is sure to hold it firmly in place. If you can't find one, try a more-common disk magnet, making sure it's completely covered in the glob of plastic . After all, you can always warm it up and disassemble it to try again.
Important! Neodymium magnets may loose their magnetism at 80 degrees Celsius. Polycaprolactone only softens at 60 degrees Celsius so you've got to keep the polymer within the 20 degree temperature window when making this. I just put some granules of the plastic in a metal dish and carefully used a hot-air paint stripper to give them the absolute minimum of heat neaded to soften the plastic. Luckily, the stuff goes from white to clear the moment it's ready to use.