Well, well..............
Work has continued on the turntable as remarkably, I have managed to stick with just one project for the last few days. I stuck the PCB squares onto the outside of the well using UHU epoxy adhesive. After 24 hours, I began soldering the well rail in place. I adapted the PCB radius arm I had used to grind the well to shape. I cut some of it away and then put a notch in it where the rail would go. I had calculated from the turntable that the radius ought to be 80mm. Here is the radius arm in action...

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My guess about the radius was perfect, as the ends of the rail met exactly. Only problem was, the wheels on the turntable didn't quite match the radius of the rail (add your own expletive here)

I had the choice of moving the wheels slightly on the turntable or making the radius of the rail slightly wider. After thinking about it overnight, I did the latter. Fortunately, this proved easier than I expected. I soldered a short piece of PCB onto the radius arm with a slot in it, positioned at 80.5mm. I then forced the rail and chairs into their new position. I was expecting distinct kinks in the rail between chairs, but this didn't happen - the curve still looks pretty smooth. It now matches the wheels on the turntable. Only problem is that there is now a gap in the rail as the ends don't meet any more. I will splice a short piece of new rail in to bridge the gap. Fortunately, this is on the viewing side of the layout (deliberately!) so the turntable wall will hide the bodge. Here is a photo before I bridged the gap. I decided I ought to test things with the turntable more or less finished before I did this - just in case I needed to make further adjustments. Here is the well, as it now is...

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There are also a few minor cosmetic things to do to the well. One was to cut shallow slots to divide the well into eighths, something like the well I am roughly basing my model on.
Next, I turned my attention to soldering the running rails onto the turntable. The table comes with two options for fixing the pivot. The first is a fixed pivot. The second (which I decided to use) allows the turntable to float slightly on the pivot, so it rides on the well rail at all times. The top of the pivot rod is embedded in a substantial boss. This has a small hole for a thin bit of rod in the top, which engages in a hole dead centre of the turntable. (see diagram at the bottom). I opened out the holes for the thin rod and tapped them 10BA. This allowed me to temporarily screw the bush tightly to the turntable. I then checked the position of the pivot very carefully, to see how central it really was. Laterally, it was spot on. Longitudinally, one end was just very slightly longer than the other - probably my fault for not filing the sleeper down far enough. I filed it down so that both ends were equidistant from the pivot.
I then made a jig to fix the position of the running rails. I drilled a pivot hole in a piece of ply and put the turntable in position, with the pivot in the hole. I then stuck some pieces of wood along one side and one end of the ply, tight to the turntable. Getting the running rails in the right place is a perennially difficult problem when making turntables, as a fraction of a millimetre error can cause serious alignment problems when the table is in use. Here is the jig

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At one end of the jig, I put a track gauge, carefully adjusted to be dead centre to the turntable. I then soldered the end chair and rail for one side - just one chair and one rail. I then turned the table around and did the same at the other end for the other rail. I then worked my way along this second rail, adding chairs until I reached the far end. I carefully checked to make sure that this rail was dead straight and in gauge with the opposite rail at the far end. I used a steel rule from an engineers square to check for straightness. This is almost the correct width for a track gauge, by coincidence. The pencil in the photo is supporting the end of the turntable.
Once I had finished one rail. I turned the table round and soldered the other rail in place using track gauges. I then carefully checked the alignment of the rail by marking where the rails lay one way around and comparing this with when the turntable was turned 180 degrees. I am within a hairs breadth of 100% accuracy, thankfully - near enough for now. There will only be one position where both ends of the turntable need to be properly aligned at the same time, but it has to be accurate, as it is the through line to the docks.
Here is a photo of the turntable on the well. This is still with the pivot firmly bolted in position.

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I can turn it into a floating pivot simply by loosening the bolt slightly, to allow the table to rise and fall slightly on the pivot. The well rail is dead flat, so the only reason really to allow the table any freedom of movement is to allow for the pivot being very slightly out of the vertical. Here is a photo of the diagram in the instructions, which hopefully makes the arrangement a little clearer than mud...

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The only modification I am making, as I said earlier is to replace the thin rod at the top with a bolt. Apart from anything else, this should prevent the turntable from falling off when I turn the baseboard upside down. The top of the bolt will be hidden by a representation of the real central boss on the turntable. I will leave the inside half-chairs until I have tested the turntable in position on the layout and made any necessary hairsbreadth adjustments.
Well, that might not be how a professional would have done it, but all seems well at the moment
