The crank is made from a piece of bright mild steel bar. For simplicity, a process to machine the off-set for the crank pin is described using some packing in the 3 jaw chuck of the lathe.
The crank pin is just a short length of silver steel rod.
To create the blank disc, a piece of steel bar can be turned down to the required diameter. Although only 6mm of length is needed, it is worth covering a bit more length to allow room for the parting-off tool.
In the same setting the centre hole for the axle should be centre-drilled, drilled and reamed to final size.
When parting off the crank disc a slow feed and speed is best.
Part way through, the tool can be retracted and a file used to deburr both external edges on the part, before continuing.
To drill the crank pin hole, a piece of packing can be used in the 3 jaw chuck to give the required off-set. Then the hole centre-drilled, drilled and reamed in the usual way.
The pillar drill can be used for this, but the lathe ensures the hole is parallel to the axle hole and removes the need for any marking out.
The crank disc is best secured to the axle using a Loctite retaining compound or similar.
The crank pin requires little comment. Just a piece of 3mm silver Steel finished to length.
The crank pin can also be secured to the crank disc with Loctite.
For more information on turning eccentrics in the 3-jaw chuck check this page which has a formula for the packing piece too.
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