Trailer stub axle

frontal views of magnet rotors for the two versions magnet block

2"x1" x1/2" grade 35

frontal views of magnet rotors for the two versions

The disks have to be held in place somehow while drilling through the hub flange and on through both plates. Various solutions have been used. One is to temporarily tack-weld each disk to the hub before drilling. A simpler approach is to mark the first bolt hole as accurately as possible by hand, and then use that to bolt the disk(s) to the flange while drilling the other holes. Fit a bolt into each hole as you go and recheck the centring.

Make an index mark to record the position of the disk on the hub for future reference during assembly. Drilling an index hole through the hub flange and both disks is a good way to keep track of the positions. Mark the faces of the disk for correct reassembly.

Finally drill three (only two shown in diagrams but 3 or 4 is better) 7/16" [10.5 mm] holes in the front plate on the same circle as the 12-mm holes, but midway between them. Tap these holes out with 1/2" thread [M12]. These holes will be used to jack the font plate on and off the alternator using long 1/2" [M12] screws. This is necessary because the forces pulling the magnet rotors together will be very large when the magnet blocks have been added to them.

Remove any burr from the edges of all the holes. The magnet-plates are now almost ready for resin casting. (See 'Casting the rotors'). Sand them at the last minute.

Drilling the magnet rotor plates

The magnet rotors consist of 12" [300 mm] diameter disks, cut out of 5/16" [8 mm] mild steel plate. 12 magnet blocks will be mounted on each magnet-plate, and encapsulated in a polyester resin casting.

If you have the disks cut out by laser, ask for a central hole 2 1/2" [65 mm] diameter. Alternatively use a holesaw to cut a neat clearance hole for the bearing stub on the hub.

\ holes/ flat on the hub flange. It is also useful to have a similar hole in the second magnet-plate. Keep the off-cut disks from the holesaw for use in the yaw bearing and tail bearing.

You can even have the stud holes cut out by the laser cutter if you know the exact dimensions. This will save a lot of hassle. Or drill them by hand as follows.

Use the hub flange as a guide for drilling the hole patterns in the magnet plates. This is more accurate than marking out all the centres of the magnet-plate holes by hand. It is important that the disk holes align perfectly with the hub holes, or the mounting studs will be skewed.

You have to centre the disks on the hub flange before drilling through. Fit the bearing hub onto both magnet-plates and revolve the bearing to check for correct centring. Prop a ruler or piece of wire close to the edge and adjust the position until the plate runs true.

The steel plates are then mounted on the bearing hub in such a way that the magnets face each other across a small gap. The stator will be mounted in this gap.

12" [300 mm] diameter 5/16" [8 mm] thick magnet block

2"x1" x1/2" grade 35

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Making the stator mould







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