Form perfect tumblehomes

I’m building a rake of ‘OO’ gauge brass carriage kits, but struggling to roll the curved profiles on the lower edges of the carriage sides. Are there any jigs available for ensuring consistent results?

George says: Forming the distinctive curved tumblehome along the lower edges of carriage bodies is a tricky skill to master. The time-honoured method is to employ a length of metal rod or wooden dowel and roll the metal to shape, in a similar manner to rolling out pastry. It’s important to work on a yielding surface, such as a stack of tissue paper or the rear of a mouse mat, to absorb the pressure from the rolling rod. Ensuring that the correct profile is formed in exactly the right place is key, but also the most difficult aspect to master. Ralph says: There’s a simple but hugely effective alternative to the traditional rolling method, using a home-made jig. It’s formed from lengths of suitably profiled decorative timber moulding, such as architrave or skirting board, and 10mm aluminium angle. The alloy is drilled at regular intervals to accept pan-head, self-tapping screws to form an effective clamp on the top of the timber, just behind the start of the curved profile. The more screws you employ, the more effective the clamping pressure. The brass carriage side is then positioned between the timber and the aluminium. The part must be aligned carefully along its length so that the tumblehome profile will begin in the right place. Having set up one side accurately, cut and fix a length of plastic or metal strip to the timber to act as a locating fence for the rest of the carriage sides, thus ensuring consistent results. A steel rule is used to press the brass over the profiled timber. The metal is bound to spring back slightly, so there’s some scope for adjusting the profile with further use of the steel rule. But first remove the side and check the profile against one of the carriage ends before re-clamping and making any adjustments.