Having made the crosshead and slidebars I'm keen to get on and start machining the cylinder. As a precursor I decided to update my 3D CAD model. Big mistake! I've spent ages correcting errors and accounting for the vagaries of the casting. On the drawings the cylinder and other parts are shown leaning back slightly to the crankshaft, specified variously as an offset or an angle. At the start I decided to bin this idea as it would make machining the cylinder unecessarily complicated. Having modelled the cylinder to get the vertical centreline of the engine in line with the crankshaft two problems arose. The flange on the bottom of the cylinder was only 1/4" thick. It would be strong enough, but is much thinner than prototype and wouldn't allow the flange to sit above any sensible thickness of cladding. The second problem was that the outer slidebar support casting was unusable - too tall. So I tweaked the cylinder model to lean back by half a degree. All the problems went away! The flange on the cylinder base is now about 1/2" thick and the support casting is right. On reflection it won't make the cylinder more difficult to machine. I can machine everything square and then at the final stage of machining the bottom of the flange just tilt the whole cylinder a bit. On the fullsize engine the cylinder tilts back slightly. So presumably the designer had the same issues of getting the cylinder to line up with the crankshaft.
On other forums there has been a discussion on what thickness of gasket to use. Although my steel boiler is made from hot extruded tube the diameter only varies by about 4 thou around the circumference. Most advice was to use a 3mm or so gasket. That seems very thick to me; I think I should be able to get away with a 1/32" gasket. To check the fit of the flange on the boiler I 3D printed just the flange from my CAD model:

I can get a 5 thou feeler gauge in between the flange and boiler in places, but generally the flange is a very good fit. More experimentation is needed, but this is a good starting point.
Some years ago I bought a face mill for the horizontal milling machine. This will be useful for roughing out the cylinder. With much BF and BI I have finally got the overarm on the horizontal mill out of the way:

Now that I've got some oil on the dovetails I can move the overarm just by pushing rather than walloping it with a copper mallet. I've also had to make a new drawbar for the face mill; M16 instead of 5/8" BSW. I might even get around to trying out the vertical head for the mill I bought some years back on Ebay:

The main issue with the vertical head is how to lift it onto the machine. That's a 12" rule leaning on it. When I bought it I managed to lift it out of the car boot and into the workshop. No way I can lift it unaided now.

At least temporarily I can get my neighbour to give me a hand but longer term I need some sort of mechanical assistance.
At the moment, partly by design, I don't have any work lined up for a few months. So once I've got my gliding holiday and my mothers 90th birthday bash out of the way I should have plenty of time for the workshop. Of course there are other calls, like the garden and house, but I can control the urge to do those jobs.

Andrew