Mount one of the smaller pulleys on the spindle just made and firmly clamp in place
using an M6 screw and a substantial washer. Reduce the diameter to 34 mm and using
a grooving tool, or maybe a rear mounted parting off tool, make a groove 6 mm wide
and 8 mm deep, Photograph 17. Repeat for the remaining two pulleys.
Now set the top slide to 14° and with a suitable tool produce the right hand face,
working to a dimension of 2 mm for the flat remaining on the outer diameter, Photograph
18. Next, remove the pulley, turn over, refit and turn the second face similarly.
Repeat for the remaining pulleys.
Reduce the drive input spindle diameter to 12 mm, as per drawing, and use to finish
the two larger pulleys as above. The drawings do though show a difference between
the smaller and larger pulleys in that the groove is narrower on the larger ones.
The reason is that the belt bottoms in the idler pulleys and the extra width give
some tolerance to cope with misalignment. The width of the grove in the main pulleys
is though crucial as the belt must only contact the sides to ensure sufficient drive.
Because of this, the viewer must check the belt being used to determine if any changes
to the dimensions are required.
Fit the bushes to the idler pulleys using a two-part resin adhesive ensuring both
ends are proud of the pulley side faces, leave to set. Next return the first pulley
to the three jaw chuck fitted with the reverse jaws and skim the end of the cast
iron insert so that it is just proud of the pulley's side surface, say by 0.1 mm.
However, it is likely that the insert on the other side will foul the jaws and prevent
the pulley resting accurately on these. A large washer with a 16 mm plus hole placed
between the pulley and the jaws will overcome this problem. Having machined the first
end, lock the saddle and leave the top slide in the same place so that the other
side, still with the washer, and the remaining pulleys can be machined to the same
Remaining items D1, D3 to D6 and D9 These are all simple parts and little needs
to be said regarding them, except that diameters and lengths of the pulley spindles
must be made to ensure that the pulleys that mount on them can run freely when assembled.
Photograph 19 shows the parts that make up the drive assembly.
With experience gained in use of the head I have decided that lubrication ducts added
to the spindles would be a good idea, see Sk. 2. If it is anticipated that the head
will find considerable use then even better would be to add ball races.