Originally Posted by Ron van Sommeren
Airgap is not only the gap between the magnet and the stator, the gap between the magnet and flux-ring has the same effect as magnet-stator airgap. Both have to be taken in account. Put iron shims in the space between the magnet and the fluxring, thus reducing the total airgap. Magnetic resistance will be lower, flux increases, less rpm/volt (=Kv) and more torque per ampere (=Kt). Also less chance of local saturation were magnet edges touch the flux ring. More glueing surface too.
Along those lines, I now glue magnets to the bell with JB Weld epoxy. Don't know what's in it, but magnets attract the stuff (will even pick up a tube of JB), so it should help in moving the flux along. Put a dab on the bell and place the magnet on it. It will squeeze out the excess. Airgap is zero, though I don't know how efficient the JB Weld is in the flux department.