After getting hold of a wood and brass half-beam engine (see separate thread) I have been looking up these half-beam engines. There are a couple of things I don't understand.
First is that the beam is a dead weight, I would have expected some sort of counterbalance on the flywheel. I suppose it is handy to always know where it will stop, but I thought they would balance it out a bit more. It may not be critical on a model, but on a full sized engine that is a heavy beam, surely it would surge on the down-stroke.
The other is that a lot of the Easton and Amos engines have the valve chest offset towards the top end of the cylinder. Why did they do that ? Easton and Amos engines dominate the pictures I can find of half-beam engines.
The problem seems to be that these engines came and went in the 1803 to 1860 slot, so maybe the literature is scarce, but some of the gurus out there must have old books and piccies.
Now I hadn't given that much thought Steve, but since you mention it ..... would the weight of the beam returning the engine to BDC at 'rest' mean that the engine was assured of being in the starting position, ie self starting? And if so, by accident or design? A fascinating question.
Good use of filling buttons Tel. The last time I made an eccentric I machined the outside on the rotary table having calculated all the angles of where to stop the table. It worked OK but quite a fiddle compared with your method.