The Sole Plate

The sole plate is the base of the engine and it has to hold the bearings for the crankshaft. The most important thing is to get the bearing supports in line, to the same depth and perpendicular to the sides of the casting.

The first task was to machine the height of the bearing support posts and the height of the standard base. This was done using the faceplate.

This first picture shows the method of clamping the work to the faceplate.

 

 

 

 

To machine the standard base, a complete revolution of the work was not possible so I just turned the chuck by hand backwards and forwards taking light cuts until the required height was machined.

To machine the bearing cut-outs I mounted the sole plate on the vertical slide and cut both seats together, to ensure they were in line and to the same depth. Whilst in this set-up I also scribed the centre line of each of the bearing seats, to aid marking out later.

The angled mount for the column was left alone, as the angle was found to be OK.

 

 

 

Next, I turned the casting through 90 degrees on the vertical slide to mark the centre line in the other axis. However at this point I found a problem. Despite machining equal amounts off both sides of the casting the standard base was not centred between the bearing mountings. Further measurement referenced to the outside edge of the casting showed that the error was 1.5mm. Even without any machining this feature on the casting was not in the correct place. Oh dear.

The picture on the right illustrates this problem and it is even more obvious when the location of the holes is compared to the position of the standard base.

More to come, on how I worked round this problem………..

 

Several weeks later…………….

I've been busy making the Cylinder and the Top and Bottom Cylinder Covers, whilst I think about this situation. Having considered several possible solutions to the offset standard base on the sole plate casting, I decided to basically carry on with everything, as normal. This was the only way I could see of getting the standard casting to sit on the sold plate and look right (they were already an exact fit). The result of this meant that from the Standard upwards, my engine would be in-line and concentric. However the miss-match would affect the position of the crank within the sole plate sides. This hand sketch shows what I mean (apologies for the metric conversion).

Crank Sketch

To summarise the sketch. The gap in my sole plate was 50mm (slightly oversize) and assuming I made the crank to drawing this would ideally leave a gap of 4.3625mm each side. In my case this meant there was room to accommodate a 1.5mm offset, the bearings would just have to be machined as so. One bearing will need to be 5.8625mm, the other 2.8625mm.

 

From a side view this will mean the engine will be slightly off-centre but I don't think it will notice. Anyway the engine is not symmetrical about this axis, with a flywheel one side and the eccentric the other, so it should look fine. I will have to make the bearings last after everything is assembled to work out the final dimensions.

All this means that the sole plate is complete for the time being.

UPDATE

Once the main bearings were made the sole plate had the bearing supports machined to final thickness by clamping the sole plate to the cross slide with suitable packing (I used a piece of Plywood and 2 shim strips.) Then 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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