Graham.
The stretcher bars are far easier to make than to explain how, but I'll try.
Materials : Brass tube, 0.8 mm OD... 0.6 mm ID from Albion.
0.6 mm Nickel Silver wire from Eileens.
0.5 mm 'Plastic Beams' from Lion Roar. ( Hard to source at present )
Tools : A set of bending form tools... the base of .015 N/S, and the 'dies' of 1 mm N/S. In the photos the upper die is soldered to the base, while the lower die is clamped in two positions as shown. NB The first image shows a completed bar half.... at the stage shown the wire/tube would be straight.
I annealed a 30 mm length of wire, and cut a 15 mm length of tube. ( I hold the tube in a pin chuck in a vice, and cut it with a very fine piercing saw using backward strokes. )
I don't remember if I annealed the tube... I do remember it burning away to nothing on one attempt.
I then inserted the wire into the tube, such that it was 5 mm short of the tube end. A simple gauging pin of 0.6 mm wire ensures consistency.
After marking the tube at 10 mm from the open end, it was placed on the jig base with the tube mark in line with the jig mark. The straight part ( A ) of the A/B die is pushed up to the tube and clamped in position.
The protruding wire and tube can then be bent around the die, using a pointed end paxolin sleeper, or other suitable pusher.
Leaving the wire where it is, the A/B die can be changed over to the B side, clamped, and the reverse bend produced as before. The wire will need some gentle easing to bring the ends into line.
You now have half a stretcher bar, with a hollow tube at what will be the track centre.
Once the second one is made, they can be joined with a length of the plastic beam, about 11 mm long.
This make of plastic rod is much less brittle than Evergreen or Slaters... it bends rather than snaps... but there may be alternatives more readily available... glass fibre perhaps?
The exact length of the bar can be controlled by fine adjustments to the rod, and then super-glued in place. The join can then be filled with epoxy, which once dressed down and painted should be invisible.
The outer wire lengths can be then trimmed to length, so they fit between the switch tongues hard up against each stock rail. The tougues are drilled at appropriate places, the stretcher stub wires fitted into the hole while the tongues are attached to the TOU. The stretchers are not glued or soldered to the tongues, so there is no stress on any of the arrangement as the switch is operated.
While it might be tempting to try, I have doubts about making these bars workable... in my case, the TOUs and droppers do all the work... and I don't think the bars would stand up to the forces on their own, especially if the switches are the more common fixed heel type.
Good Luck ! Steve.