Many thanks for the encouragment everyone! The next bits are the timing case and its cover which are better made as a pair to get the outer shapes to match closely. The detailed shape isn't all that critical but any misalignment will stick out like the proverbials.
As usual the parts started as squared-up billets, marked out as carefully as I could using slip gauges on the surface plate. Then into the mill to bore the holes for the cam- and crankshafts:
Building a nest on the mill-drill table means you can bore the holes for the auxilliary drive shaft for the contact breaker and the oil pump from both ends and be sure of them lining up:
Then on to the faceplate to bore out the chambers for the timing gears:
setting the depth of the bores with slips from the saddle stop:
and digging out the chambers:
When I tried the timing case on the crankcase the shaft centres didn't quite match the centres of the holes that have to clear the bearings (sorry, no picture, I was thinking "Oh bother", or words to that effect, at the time and worrying about how to correct things). Time for deep breaths and careful measurement:
It looks like the only thing I got spot-on on the crankcase was the shaft centre distance (phew!) the shafts were 10 to 20 thou off centre in the block, not a lot but then I'd goofed with setting up the timing case for the very first bores. May have messed up the arithmetic with the edge detector, don't really know. Anyway, there was just enough metal to re-bore, so back into the mill:
With that experience behind me I marked out and set up the blank for the cover plate
very carefully and drilled and bored the main holes and fixing holes:
Most of the cover plate is only 1/8th" thick and I removed a lot of material in the mill:
before turning a steel mandrel to locate the plate from the distributor mounting hole and turn away the rest to thickness:
To get the outsides of the case and cover to match the final fixings were drilled and tapped:
and the fixing screws used to keep everything lined up while the outside was carved to shape:
The surface finish from the face mill isn't the best (probably needs flood coolant) but I'm less concerned with this now; my experience so far is that the surface gets damaged with further clamping etc and will need a final clean-up anyway.
The products look like:
The "family group" this time is slightly faked using Blu-Tack as I want to leave drilling the fixing holes into the crankcase until I can check the meshing of the auxilliary drive gears:
With this experience of setting up errors a DRO for the mill, plus an electronic edge finder, have gone on the Christmas list!
I think I need a rest from carving Al alloy for a while and the next bits will be the camshaft, tappets and timing gears.
DT