The crank prototype was good but had some flex and wobble and was made from mahogany and a found broomstick.
The crank prototype was good but had some flex and
wobble and was made from mahogany and a found
broomstick. It has threaded bar screwed to the end disks
to mount the bearings on.
The final crank is made around 25mm oak dowel shaft and has oak disks.
The dowel pegs push through the sides of the disk and fix tight the shaft,
they are doubled up in this one and make it super strong without glue or
screws. A 25mm bore bearing fits snugly on the shaft.
The disks are first CNC cut, then hand drilled in an accurate drilling jig to
make sure the multiple holes for the dowels meet up – As our drill drills at
a slight angle this is actually advantageous, as the inaccuracy means that
the pegs fit very tightly in the hole.
To take this to pieces all that is needed is a few taps with a small hammer to
remove the dowel pegs.
The disks are the slid into place on the 3 dowel shafts. Once the spacing is
right the holes are re-drilled so this time making holed in the shaft for the
dowel pegs, after the pegs are tapped in, the excesses dowel is removed
using a Japanese saw leaving the 3 shafts.
The piston crank in its final form!