A final hour in the workshop saw me start looking at fabricating some coupling rods. As a teenager, I bought a copy of
Model Locomotive Construction in 4mm Scale by Guy Williams, who built many of the locomotives at Pendon. In it, he discusses using bullhead rail to make fluted rods, and I have a few lengths of Tenmille 32mm track, bought online in error...

So I cut a couple of lengths roughly to length,

filed concave faces onto the ends, and drilled/parted off some 8mm diameter brass bar for the ends.

The precise length of the coupling rods should be the same as the distance between the wheel centres. I still have a little filing to do.

But that can wait until tomorrow. I think I'll have to get some hard ('silver') solder; this is just balanced in position.
