After a long pause for thought, I have moved on to the larger curved baseboard components. Three to do -

(1) the 'S'-shaped backscene for the larger scenic board

(2) the combined backscene and baseboard side for the second scenic baseboard

(3) the spline for the track bed on the second scenic baseboard.

First off is the 'S'-shaped curvy backscene. This has to be fairly robust for a variety of reasons. I am making it out of 3 layers of 2mm MDF. More robust than your average backscene, but it needs to keep its sophisticated shape. I had to form it before any track is laid, because the flat baseboard is the template for the shape of the curves. I can't fit it permanently until after the track is laid though, as it would impede access to the baseboard top.

I first did a dry run to assess any problems. The clips are screwed to the baseboard top. This is the view from the public viewing side. The backscene will be 150mm high, which looks about right from first impressions.

After a dry run, I added a few extra temporary supports, glued the 3 sheets together with wood glue and put the backscene in position. I added extra clamps etc. to hold everything together. It will now stay like this for 24 hours or more. I used Gorilla wood glue, which stays fluid long enough to slide everything into place and clamp it.

The structure is held 10mm above the baseboard surface, so that I can easily remove it when ready. 

First impressions are that it has worked pretty well. Everything seems vertical - and more or less follows the 'S' shape printed on the baseboard template. 

I have also been thinking about the turntables. I bought some bearings off Ebay which may help. The photo below shows one of them. These are 140mm in diameter. The turntable in the fiddle yard will be surface-mounted. I drew up a full-scale template showing where to place screws etc. when I put everything together. 

The fiddle yard turntable will be manually operated, so should be fairly simple to fit. The one on the scenic section will require full scenic treatment, so much about its mounting and operation will have to be different.

Next, I shall have a go at the spline for the track bed on the second scenic baseboard. This will be 20in radius. I shall make a simple jig from an old worktop surface to form this - or at least that is the plan!