With baseboard construction phases 1 (scenic board) and 2 (legs) complete, I've made a start on phase 3: the fiddle yards.
I had decided that turntable style yards would be the most convenient operationally, with all locos needing to face the direction of travel (I assume there would have been a turntable at the Ullapool terminus). The first hurdle to overcome was cutting 35cm-diameter circles from 6mm ply for the turntable surfaces.
A little research showed that a practical way to do this was with a router constrained by a trammel. I picked up a cheap router for £30 which I am very happy with and has done the job nicely: certainly the loudest and most powerful piece of woodworking kit I now own! It came with a 6mm(-ish) bit so I used that. It also came with a "circle-cutting" attachment, but the maximum diameter was, of course, 33cm. So I made up a simple trammel from a scrap piece of ply, which screws securely onto the router base, and is bolted through a hole at the centre of the workpiece.
Following received wisdom (on YouTube) I made several shallow cuts rather than trying to do it in one. The vacuum cleaner attachment was fantastic at removing the sawdust as the cut progressed.I now have two finished turntables, and their approaches. For simplicity I opted not to cut the latter out separately, so they have slightly the wrong radius, but I can correct for this with the layer of balsa I (currently) intend to lay as a track base on top. Note that the track approach is at a different distance from the front of the baseboard at each end of the layout. The approaches also differ in that one will be double track, the other single track. Experiments with Templot have convinced me that there is sufficient length to "splay out" the double approach tracks to meet the turntable at the correct angle. I'll trim the turntables down to the required width in due course.