The cranks were set back between centres for finish turning the shaft diameters then held in a collet for drilling the intake hole. Finally set back in the fixture the crank-pins were brought to diameter. The fine tolerance on the bearing areas was achieved by stoning with a pair of fine grade thin flat India stones.
With those ops completed a simple fixture was made to hold the shafts for drilling the inlet.
Set at 20 degrees the hole was 'drilled' though first using an FC3 cutter .
Then the fixture set on its side to machine the inlet timing area
Then the fixture set on its side to machine the inlet timing area
And finally set back between centres to screw cut the shafts. Nothing special - HSS ground tool and the tool pulled out at the end of the run ie no run out groove for maximum strength.
Incidentally if no chaser is available to clean a thread the flanks can be polished to a degree by using the end grain of a piece of wood charged with carborundum paste. Pushed hard into the work the wood will run along the thread until the end.
The three finished shafts ready to fit.
I thought it best to finish off the steel parts - rounding off the characteristic 'Oliver' ball ended compression screw - the GFS tool, hardened but not tempered, cuts really well. Note this is En1a - not En8 which I had called for on the drawing below!
Removing the parting off pip by rotating the tool
Finished comp screws - all screw cut to a tight-ish fit in their respective heads
Part one here. Part two. Part three. Part four. Part five. Part six. Part seven