At this point I am going to deviate from the novice approach and rather than use
the method proposed on the Stuart drawings, to detail a method that is much more
satisfying to complete. The difference is that the simpler approach is fabricated
whilst the method I am about to suggest is made from one piece of steel. The one
making the engine can chose which method to adopt as the fabricated version needs
no more detail than that given on the drawings, the one piece method will though
give greater satisfaction.
Cut a length of 1” x 3/8” steel 3-3/8” long, carefully file the ends and centre drill
both ends as follows. If though you prefer your crankshaft not to have centre drilled
shaft ends when finished start with a length of 3-7/8” so that they can be machined
away at the final stages. Mount the length of material on the top slide, packed up
to centre height, and with a centre drill in the drill chuck position it such that
its larger diameter just touches the materials rear edge. Traverse the saddle so
that the workpiece is clear of the centre drill and then, using the cross slide,
move the part 5/16” plus half the centre drills diameter and centre drill the end
of the workpiece. Traverse the cross slide by a further 3/16” and centre drill once
more. Remove the workpiece, rotate, refit and centre drill the other end similarly,
If working between centres is a new technique to you a major benefit of the method
is that the part can be removed, replaced, perhaps turned end on end and concentricity
is maintained perfectly. Heat thought is developed and the part will expand so the
tailstock needs resetting periodically. If you do not have a rotating tailstock centre
it will also need lubricating to minimise the heat generated at the centre itself.
Fit the Catch plate, or a faceplate with a suitable driving peg, and both headstock
and tailstock centres and place the workpiece between these using the central centre
drilled impressions. If you do not have a suitable driving dog for this size of material
drill a hole, say 5.3mm for an M5 screw, in the eventual waste material near the
end and fit a short length of steel to provide the drive.
Machine the outer edges reducing the width to 13/16” and thereby also producing the
curvature as shown on the drawing. Only doing it just past the position for the
webs, Photograph 62. I say “as shown on the drawing” but the radius produced will
be 13/32”, the drawing calls for 19/32” but this is of no importance.
With that completed, mark out the position of the webs, both inside and outside,
similarly the width of the shafts and rough cut just outside these marks to minimise
the machining necessary.
Do not though take out the portion between the webs at this stage but drill a 6mm
diameter hole to assist with the eventual opening up of this space, Photograph 63.
Ensure you drill the hole in the correct place, that is nominally in line with the
shafts, or it may be a case of start again.
Return the part to the lathe and turn the shaft to 19/64” at this stage and face
the outer face of the web, Photograph 64, remove, rotate and repeat.