by Nick Dunhill (Experienced modeller and a member of the GOG Technical Committee)

Some modellers are hesitant in tackling etched kits, thinking that forming or reshaping the etchings might be tricky or require specialist tooling. Here is a straightforward demonstration of how to go about the process (photo 1). The cab roof in question is from a Martin Finney T9 kit and it requires a reverse curve at the edges (photos 2-3). The principles are the same, though, for all cab roofs. Rolling bars are not required as roof etchings are too short and thin. There is no need to anneal a roof etching as it is thin and the curve is shallow.

Photo 1 – Rolling the etching

To form the curve use a rod of a suitable diameter (around 20mm), on a yielding surface. A kitchen rolling pin and a pile of magazines on the carpet are ideal. Place the etching on the magazines and gently roll the bar over it in the direction of the curve. Use light, even pressure (not too much), and keep the bar square to the etching. Check the curve against the cab front and sides, the rear if you’re forming a tank engine roof, and any roof formers if provided. Roll again as necessary until the curve of the etching allows it to sit nicely on the cab. You can gently ease with fingers if necessary.

Photo 2 – Making the folding bar (if necessary)

Offer the formed etching up to the cab front to determine where the reverse curve is needed and mark with a felt tip pen. Choose a suitable strip of scrap to make a folding bar and use a file to form a gentle radius along one edge. Fold the strip in half with the radiused edge to the inside. Sandwich the etching inside the folding bars with the pen marks to the top.

Photo 3 – Forming the reverse curve (if necessary)

Carefully place the folding bars and roof in a vice with the top of the folding bars level with the top of the vice jaws. Check the alignment one final time and tighten the vice. Form the curve using a solid rectangular block rotated firmly against the top of the jaws and the etching. (The photo shows an engineers’ square base; a metal or wooden block would work equally well.) Check the profile against the cab front and adjust as necessary.

Photo 4 – Top of the finished roof

This shows the top of the roof with all the beading applied and solder cleaned up. In the case of this kit, the beading helps to form the correct curve.

Photo 5 – Underside of finished roof This shows the underside of the cab roof with all the internal beading applied