The first time I assembled the engine truck, it was held together mostly by fervent prayer while the epoxy set. The result was as shaky as my belief in prayer! Perhaps if I were more spiritual, this would be a good strategy for me.
The second and third attempts leveraged a new pair of jigs that I constructed. They consist of two hex rods that are exactly the right length to fit between the engine truck journals, and bolts that pass through the bearings to hold the side frames against the hex rods. While the epoxy cured, I sat the assembly atop a piece of brass bar that was the same width as the hex rods. If I had been smarter, I would have made the hex rods bigger than the bolts, and then I wouldn’t have needed the riser bar.
The result was much more parallel than the prayer version. Also, I’m thrilled to report that the flexure works! Under the weight of the boiler the truck can accommodate an unreasonable 1mm bump and still keep all four corners in contact with the ground.
Why, did I need a third assembly attempt, you ask? Well, on the second attempt, I forgot to glue one of the joints – proof that whenever you invent a foolproof system, someone will invent a bigger fool.