Said in best Victor Meldrew voice, as the first bogies is now 95% complete and all appears to work as intended!   The sideframes aren't glued in place yet, merely held in place by the spring pressure and the location of the axleboxes/equalising beams, but it performed successfully in a few hand propelled tests last night. I can run the bogie over an obstruction of 1.5-2mm, with all other wheels remaining in contact with the ground as demonstrated in these pics:     The bottle of flux w