After a bit of fettling of the jig I think I have cracked it. The four lengths above are the work of an evening - about 2 hours which I am pretty pleased with. Tinning everything first was a key to getting the neatness. The length on the right doesn't have chairplates fitted - it was the first length in the "fixed" jig and since it worked, I did the other three with chairplates.
Now to work out how much I need and to get some ply for the frame I have... School holidays soon so I am hoping for a 2mm Christmas - but will have to organise one more Cl 24 axle so I have a loco.