You're welcome Andy....
With this engine I've tried to reduce the flywheel overhang to a minimum by using 15x2 mm Gauge plate for the shutter actuator. The bearing support yoke had just enough metal for me to mill a 15mm wide slot to help guide the arm just below the crankshaft. A second vertical slot was milled in the arm to help keep it gently tensioned against the flame port below.
I Silver soldered a section of the Gauge plate at right angles to cover the flame port. I'm also using an upward shutoff in the hope there'll be less flame disturbance.
I had several cam discs cast and like Jo I found them to be almost unmachinable. An overnight soak in the multi fuel stove and a decent Carbide tip found us a disc, hidden inside. But there's a tale....
I used your method of creating the cam profile ( 4 jaw chuck ) but when I offered it up to the engine I discovered I hadn't given quite enough lift. Back to the lathe for another swipe and disaster, a hidden hard spot caught hold of the tip and bang, cam disc trashed.
Not having much of what Jo refers to as " scrapbinium " ( Castings man )
I was at a loss. Luckily I still have many leftovers for the Robinson hot air engine, a crank disc was found and duly machined.
Oh what a joy it is to machine " Good Iron " no dust, no sparks just neat little curls, in no time at all I had a replacement cam disc and one that worked as well.
Just a few little " tweaks " should see a close to this thread....
Cheers Graham.