The sole plate had to hold the bearings for the crankshaft and support the engine standard.
It is important to get the bearing supports in line, to the same depth and perpendicular to the sides of the casting to ensure the crank will not bind. The engine standard base also needs to be as square as possible to ensure the piston rod will line up with the crank.
First, the height of the bearing support posts was machined and the height of the standard base. This was done using the faceplate and the photo shows the method of clamping the work to the faceplate.
To machine the standard base (arrowed), a complete revolution of the work was not possible, so the chuck was turned by hand backwards and forwards taking light cuts until the required height was achieved.
To machine the bearing cut-outs the sole plate was mounted on the vertical slide. Both seats were cut together, to ensure they were in line and to the same depth.
During this set-up, a centre-line was scribed in each of the bearing seats, to aid marking out later.
The angled mount for the column was left as is.
Problem.
As the casting centre line was marked in the long axis, it was noticed that the casting was not symmetrical. The standard base was not centred between the bearing mountings. Further measurements referenced to the outside edge of the casting showed that the error was 1.5mm.
The result was that the crank would sit offset in the sole plate by 1.5mm.
So with the gap in the sole plate at 50mm and (assuming the crank would be made to drawing) there would be a gap of 4.3625mm each side. However to accommodate the 1.5mm offset, the bearings would be machined to suit.
One bearing would need to be 5.8625mm, the other 2.8625mm.
Finally - Once the main bearings had been made the sole plate had the bearing supports machined to final thickness by clamping the sole plate to the cross slide with suitable packing. The sole plate was checked for squareness and the bearing supports were machined to the thickness of the slot cut in the bearings.
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