Click on drawings to download - for personal use only.
SUB BASE
Start by cutting a piece of 6mm aluminium a little larger than the 110mm required, locate the middle and dot punch. Mark out a 110mm circle with a pair of dividers, roughly mark 45degree lines and saw off the corners.
Clamp the plate to the mill table with some packing underneath then proceed to drill the four M3 clearance holes and the four 4.0mm holes which will be used to mount the engine to a wooden display base. Then with an 8.0mm dia milling cutter counterbore the 4.0mm holes 3mm deep and also cut a flat bottomed hole 2.0mm deep in the middle of the plate to locate the valve spring into. If you have a larger spring then make the hole to suit. Once removed from the mill table the underside can have the M3 clearance holes countersunk so your screw heads sit just below the surface.
Screw a piece of ply or MDF to the lathe faceplate of if you have a large enough 4jaw then the board can be held in that, use the tailstock centre in the dot punch mark to hold the plate to the board and then screw it on through the 4.0mm holes and turn the outside down to 110mm diamater.
Blue the plate in a couple of places and then offer up the base using a couple of screws in the M3 holes to line things up and scribe on its diameter.
Swing the topslide right round and set to about 4degrees then taper the edge of the plate until the cut runs out where the scribe marks are.
The last turning job is to add the decorative moulding to the edge which can be done by grinding up a small HSS form tool.
Finally back to the mill, pop two drill bits into the 4.0mm holes and locate them against one of the T-slots then locate the middle of the plate. Using the 8.0mm cutter again cut the other half of the exhaust passage 3.0mm deep
A picture of the two parts together, details of the spring later.
Part one here Part two Part three Part four Part five Part six Part seven Part eight
Part nine
