Those not having a boring head could bore the hole on the lathe with the arm mounted
on the cross slide and a small boring tool mounted in the four jaw chuck to provide
size adjustment. Whilst not the quadrant being machined, Photograph 3 shows a typical
example of the method, an angle plate would of course be required to support the
Photograph 4 shows the recess being made for the secondary arm, with the slot also
having been made at this setting. The photograph also shows two holes that had been
drilled for the eventual corners of the areas that I shaped. For this I removed the
bulk of the metal by using a bandsaw, with the cut edges then finished on the milling
Produce the curved slot in the secondary arm using a rotary table. or if one is not
available by drilling a series of holes and finishing it by filing. Having written
this, it occurs to me, that if a rotary table is available it could be a third method
of making the 46mm diameter hole, and quickly.
After making the clamp, having made it initially 17mm long and without the radius,the
bush is the next item. First turn the 46mm diameter to be a very close fit in the
46mm diameter hole in the main arm and 10.2 long, part off at around 25.5 long. The
extra 0.2mm length over the thickness of the main arm is an allowance for riveting
the bush into the main arm. Making the bush at this stage is best as it is easier
to make this fit the main arm rather than making the main arm fit the bush.
Next, make the recess, hole and tapped hole, for the clamp and fit the clamp. Then
return it to the lathe, holding it on the 46mm diameter, and through hole bore,this
making the radius on the clamp in the process. Do though previously measure the boss
on the gearbox and accurately make a plug gauge to this diameter for checking the
through bore. The clamp can then be reduced in length ensuring that it will grip
the gearbox boss.
Next, very lightly countersink appropriate holes, say plus 0.5mm on hole diameter,
and rivet the bush, and the secondary arm, into the main arm, and file flush, and
the quadrant is finished.