As the depth of the line will be very shallow, its appearance will vary markedly
around the dial if it is not running true. Because of this, calibration should follow
on from turning the outer diameter. Also, this allows the dial to be very lightly
skimmed with a very sharp round nose tool to remove the burs produced by the operation.
Photograph 16 shows the finished result.
C1, C2, C3, and C12 These, all being simple parts, need no comment. C5 is also
a simple part but do delay drilling for the handle until after final assembly. This
will enable the hole to be drilled in the most suitable place ensuring the two handles
do not clash when tightened.
Drive Assembly AS2
Pulleys D2 and D7 First, make the three cast iron bushes for the idler pulleys.
Bore the 10 mm bore and then the 15 mm outer diameter, this ensuring that inner and
outer diameters are concentric. Part off at over 14 mm, say 14.5 mm. Do though see
my later comments regarding using ball races.
Cut three pieces of 35 mm diameter aluminium, 14 mm plus long and face either side
to a thickness of 14.1 mm. Using the three jaw chuck fitted with the reverse jaws
will give a step against which the part can rest. Return each one in turn and with
the saddle locked and the top slide not adjusted the three can be finally faced to
14 mm. Repeat this process for making the two larger pulleys, but at 60 mm diameter
they will probably use a different step on the three jaw, hence the reason for doing
Again return the three smaller pulleys to the chuck and bore to approximately 14.8
mm diameter. Leave the final one in the chuck and finish the bore to 15.1 mm diameter.
Lock the cross slide at this diameter and bore the remaining two at one pass thus
ensuring all three are the same diameter. Repeat this for the larger two, this time
boring 12 mm diameter. The 15.1 mm diameter bore provides space for a film of adhesive
between it and the cast iron bush. Leave the pulleys at this stage for the moment.
Drive input spindle D8 Place a piece of 20 mm diameter steel in the three jaw with
around 20 mm projecting and turn to 15.1 mm diameter as opposed to the 12 mm diameter
on the drawing, also drill and tap the M6 hole. Do not remove from the chuck as this
can now be used as a mandrel to hold the three idler pulleys whilst the grove for
the belt is machined.