Now that I'm moving on to the rest of the ;loco, I've changed the title to reflect that.
While working on the preparation for making the frames, I started looking at the cylinders to try and work out how I was going to fix them to the frames. I'm hoping to make a cylinder and slidebar assembly so that the assemblies can be completed off the frames, then fitted to the frames.
While pondering all the possibilities I was also looking at the detailing of the cylinders - especially the front cover with its shaped centre and the very obvious eighteen 1" Whitworth nuts holding the cover on, which were not hidden. At the same time, Mick was discussing the representation of nuts and bolts on his standard cab and I started trying to work out how I would do the nuts on the covers. Richard (Dikitriki) pointed me at the Scale hardware products but of their two smallest products, one was just too small and the other was just too big. I could have taken a punt on either the smaller or the larger and hoped that whichever would have looked OK. But fitting the Scale Hardware nuts on bolts would require drilling 0.3mm or 0.5rmm holes and that required yet another search to find a source of drills at a cost I could stand.
I then remembered something I had done a year or so ago - machining wagon strapping including bolt heads - to prove something in a discussion with Simon Dunkley. I can't remember which thread it was, so can't find the discussion, but the memory was enough to get me starting to think about milling the lot in one go - and here's the result.
The excerpts from two pictures and the extract from the cylinder GA shows the front cylinder cover details. Dougal Drummond liked his shaped pistons and the Caledonian kept the design - the pug class was designed and built more than twenty years after he left the Caledonian.
First I turned up brass blanks as bases for the cutting.
The widest diameter is the outside diameter of the cover, the next diameter of 8mm will fit in a 8mm hole in the cylinder body. The long 6mm diameter is to hold in the machine vice and this will be cut off after machining.
The blank held in the machine vice with a 2mm Plastikard spacer under it. This spacer lets me touch off for setting the tool height to the bottom of the cover outer diameter and also gives a "soft" base in case a cutter goes a bit deep.
The 2mm cutter doing the first cuts - basically the rough shaping of the protruding centre and the height to the top of the nuts and studs.
The result after the 2mm cutter has finished, with a rough cut of the centre shape beginning to show.
After the 1mm diameter cutter has finished, with the recess around the central shape deepened and the outside edge has also been milled true.
The o.5mm cutter has started to cut the nuts and studs.
The 0.5mm cutter has finished leaving just the central shape to be finished with the 0.6mm ball end cutter.
The finished result. The apparent roughness around the nuts is actually reflections of the milled surface finish. I'll try and get a better shot in daylight tomorrow. I might look at making the height increments on the finishing cuts of the 0.6mm ball end cutter a bit smaller to reduce the ridging effect which you get with these cutters - which is apparent on the central shape.
The nuts are 0.61mm across flats and the diameter of the cover is 9.13mm, to give you some idea of the sizes. I'm not sure how they will survive under a coat of paint.
I've also just realised that there was a cover over the deeper part of the recess. I've actually machined the seatings for the cover but I reckon I'll change the code and machine the cover in situ - it will make the machining a bit shorter.
Jim.
but I do get the gist of things 
.
