Stuart No 1 - Sole Plate


The sole plate had to hold the bearings for the crankshaft and support the engine standard.

It was important to get the bearing supports in line, to the same depth and perpendicular to the sides of the casting to ensure the crank would not bind. The engine standard base also needed to as square a possible to ensure the piston rod would line up with the crank.

Sole Plate partly assembled.

 

 

 

 

 

 

 

 

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 the chuck was turned by hand backwards and forwards taking light cuts until the required height was machined.

 

 

 

 

 

 

 

 

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 alone, as the angle was found to be OK.

 

 

 

 

 

 

 

 

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 measurement referenced to the outside edge of the casting showed that the error was 1.5mm.

The picture on the right illustrates the problem. The offset of the standard base can be seen when its position is compared to the hole locations

 

 

 

 

 

 

 

 

After considering several possible solutions to the offset standard base the decision was taken to carry on with everything as normal. This would ensure that the standard could sit on the base without looking mis-aligned, but this would mean that from the Standard upwards the engine would be slightly off centre.  

The consequence of the offset standard position was that it would affect the position of the crank within the sole plate sides as this sketch shows.

To summarise the sketch. The gap in the sole plate was 50mm and (assuming the crank would be made to drawing) would leave a gap of 4.3625mm each side. However to accommodate the 1.5mm offset, the bearings would just have to be machined to suit.

One bearing would need to be 5.8625mm, the other 2.8625mm. 

Click for details

               

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.

Machining the bearing supports to final thickness.

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