MJM, its good to hear from you again!
The HP cylinder block now has more holes and most have threads tapped in them. The valve end covers and valve bonnets (four of each, two steam and two exhaust) are each held on with six 8BA studs, the steam and exhaust chest covers each have 12 at 6BA. There are four more 6BA for the dashpot body and four 5BA for the steam lever trunnion:
so far no broken taps (whew)! However, if I'm going to attach the cladding with fasteners anything like scale size there will be a bunch of holes for 12BA screws to tap into cast iron, those can wait - and maybe there will be a way to avoid the problem (can't find a chicken emoji)...
The valve bonnets and other protuberances were all turned from the solid. The shapes are either small and fiddley or quite complicated to make with shallow external tapers and the machining sequences needed a lot of thought. I started with the end covers which were made in pairs on stubs of steel:
with the six holes drilled deep enough for both bits to be parted off:
and after parting super glued to a fixture for finishing the outer sides:
The valve bonnets were tackled similarly:
but with a seating formed to take an O ring to seal on the valve spindles. The little "boring bar" here is a 5/32" D bit which worked well:
The original drawings show the steel cladding butting up to the outsides of each of these pieces, getting that to look good sounded difficult. A pause for thought and I remembered taking a lot of pictures of the Stott engine at the Anson Engine Museum and this one shows that there the bonnets etc. are rebated to go over the edges of the cladding and over the brass edging:
Problem solved - I hope. All the bits had a small recess turned in them for this:
Whilst the exterior bits were still cylindrical and easy to hold the stud holes were drilled:
and then (finally!) the parts were glued to the fixture and turned to a slight taper for appearance:
With some studs made and temporary screws elsewhere the little family now looks like this from the valve gear side:
and, from the other:
At a bit of a guess this assembly is going to take a quarter to a third of the total build time, which may explain the length of this post and the length of time since the last one. I hope you're all still with me!
Regards, David
