The flywheel shown here was made from an off-cut of cast iron bar, but actually any material will work, the heavier, the better.
None of the dimensions are critical but the method described will ensure that the flywheel runs perfectly true when mounted on the axle.
The flywheel was secured to the main axle with a grub screw.
The bar blank should be mounted in the 3 jaw chuck and the face skimmed to run true. The centre hole can then be centre-drilled, drilled and reamed to final size in the same setting to ensure it is perpendicular to the machined face.
Next the flywheel should be reversed in the chuck and the other face skimmed to run true.
To get the flywheel running exactly, we need to take out any error there might be in the chuck jaws. This can be done by turning an arbor to suit the flywheel centre hole.
A sharp tool should be used to ensure there is no radius at the root of the arbor shaft, and a thread added on the end to take a nut.
Once machined, the arbor must be left in place until the flywheel is finished as moving it would mean it would lose its position exactly on the lathe axis.
The flywheel should be mounted on the arbor with the first machined face (the one perpendicular to the axle hole) at the back so that it sits squarely.
A nylon washer or similar, can be used to provide grip and the nut tightened to hold the flywheel to the arbor.
Light cuts are needed because of the flywheel is only driven by the friction on the arbor.
The grub screw hole is just drilled through the rim to clamp the flywheel to the shaft.
The rim needs to be marked and punched.
Alignment in the drill press can be done "by eye" with a small square as shown.
It is wise to counterbore the hole too, to reduce the length needing to be threaded.
When fitting the flywheel to the axle, it is a good idea to put a small piece of soft material in the grub screw hole first, so that the screw doesn't mark the axle. A small piece of brass or aluminium is ideal.
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