Jigs for the rotors
PCD jig for drilling holes
The magnet rotors are mounted on a bearing hub (see diagram 10). The hub has a
flange with holes in it. For example there may be four holes on a 102mm (4 inch)
'pitch circle diameter' (PCD). Or you may have some other arrangement. This will
depend on what kind of hub it is. Here we shall say 102mm PCD.
10. THE BEARING HUB PCD
PCD
HUB
SPINE
SHAFT
REAR ROTOR
FRONT ROTOR
The PCD jig will be used to drill holes in the rotors etc.
It will also be used to balance the rotors.
The holes must be marked and drilled very precisely. (See diagram 11.)
• Cut a square piece of steel plate 125mm by 125mm.
• Draw diagonal lines between the corners and mark the exact centre with a punch.
• Set your compasses at 51mm radius (or to suit whatever PCD). Draw a circle.
• The diameter of the circle is the PCD of the holes in the hub.
• Punch both places where one line meets the circle.
• Set your compasses at 72mm. Mark two points exactly this distance from the
first two, on the circle. (If you have a different PCD, this size would not be
72mm. Find the size by trial and error.)
• Drill four holes exactly 72 mm apart on the circle. Use a small drill first and
then a larger one.
PMG manual
page 13
June 2001