Well it's been a long time coming ...
The physical turntable is now done and I'm starting on the wiring over the weekend and at the same time laying the fiddle yard tracks and wiring that - a giant step for me!
Back to the turntable, with aplologies for possibly trying to teach grannies to suck eggs I'm detailing my construction, partly because although I'm handy around the house this is the first bit of actualy railway modelling* I've done in about fifty years!
So, there are four elements: the turntable itself, the deck or platter, the baseplate and spacers plus the nuts and bolts to hold it all together:
The first issue was marking a centre on the deck after tracing out the circumference on the baseboard and then cutting it out, the crosshairs used to find the centre serve as guides for laying the track and locating the bolts that will align the TT to the tracks:
Once cut the turntable was a snug fit - too snug in fact as this stopped it from turning freely, especially when the deck was atached - so more work with the saw to enlarge the hole ...
The turntable comprises two hard plastic discs fitted together with ballbearings in a race indie to make a smooth turn. Each disc has three lugs for attaching, one side is countersunk. I fitted the bolts in these prior to attaching the upper side of the TT to the deck with self tapping wood screws. I hindsight I should have either secured these nuts with Araldite or similar or used the countersunk side for the wood screws and used flat headed bolts on the basplate side and secured these both sides with locknuts. As it happend the bolts fit though a very tight fit in the baseplate that they don't 'slip' when being bolted up tight.
Off for a tea break now ...
* I've also built the station buildings, etc. from Metcalfe kits, not sure if that counts