Soldering Live Steam

Dear customers and friends of Wrightscale, we are sorry to announce that we can’t attend the 16mm AGM and convention at Peterborough this year.

Photo of 16mm Wrightscale Wren The 16mm AGM has been the high point of the year for Wrightscale since the 1990s, a chance to meet our friends and customers, make sales and purchases and keep up with events in general. Your valuable feedback has also been important, usually complimentary, but sometimes critical. We appreciate everything you have to tell us. We took the hard decision when we found that the country wasn’t opening up from lockdown as fast as we had hoped. In spite of all the precautions and vaccinations, COVID seems to be spreading again. The Westminster Government is putting restrictions in place. The Holyrood administration is also banning Scottish travel to certain parts of England. When one ban is in place, more will follow, It was a case of looking at a rising graph and wondering how it would look a week from now. If it were just ourselves we should consider, we might have taken the risk – we have had our Astra-Zeneca-Oxford jabs. There are, however, going to be two thousand of us passing through the hall, traders, public and stewards. We felt it was unfair to come into contact with strangers and pass on some combination of virus which might turn out to be unhealthy. We hope our friends will stay in touch by telephone or email, In our last blog, we were considering the challenges of sticking a locomotive together. There is no ‘one size fits all’ glue or solder. For the Baldwin Gas Mechanical model, a locomotive that is operated by electricity, low-melt solder (max 400 degrees Celsius) will do. At a pinch, glue could be used throughout. For Live Steam, such as the Wrightscale Wren, a selection of tougher solders are required. The prototype Wren was designed as a small, light locomotive for temporary track. It needed good adhesion so that it could pull long trains of small wagons, but high speeds and long endurance were not so important. The main use of the prototype was the unglamorous job of hauling skips off a construction site.

Here is a Wren, Thomas Wicksteed built to authentic prototype plans, photo courtesy Jim Hawkesworth. We can see how the prototype satisfied the criteria. What was needed was a locomotive with a small wheelbase. It had to be light so that it could be used on poor track but have a minimum number of wheels to ensure maximum adhesion. Thus the 0-4-0 T configuration, no tender, no trailing truck, all weight concentrated over the driving wheels. The frame of the prototype was therefore small and light, as is the frame of the model. After discussion about building a satisfactory 16mm model, David Smith of Modern Outline kits drew up a design based around nickel silver etches. Nickel silver is malleable and ductile – bendy to you and me – but the genius of a David Smith design is that once the metal is folded up and reinforced where necessary, it becomes rigid. There is a big ‘but’. The folds must be perfectly aligned so that the forces applied to the model behave exactly as calculated. A David Smith etch anticipates this requirement. Each piece is etched right through at its edges and at certain other places – more later - but only partially etched at its foldlines. The frame part can easily be cut from the matrix and then easily folded up. When we say ‘easily’ there are certain considerations. While the frame is still flat, check the holes for the bearings for size and open them out slightly for a snug fit. Malcolm recommends using a vice with smooth jaws to do the bending so that the metal is always fully supported. Several parts are needed to complete the frames; with care, they fit together thanks to the slot and tab construction. Each tab on the outside of a part can be placed into an answering slot etched inside another. This sub-frame is reinforced with overlays.

Photo of 16mm Wren chassis by Malcolm Wright Before soldering up, the axles and wheels should be ‘tried for size’ then comes the first solder. We recommend a high temperature; otherwise, as further parts are soldered on, the first solder will melt. For the Wren, this would mean ‘silver solder’. Malcolm recommends Carrs 188 silver solder paint – also known as paste. Soldering takes place at temperatures higher than 618 degrees Celsius – more likely 740 degrees. It will of course stay firm if low-melt solder (up to 400 degrees C) is used subsequently. The parts to be soldered should be thoroughly cleaned before and after. Always wear gloves and proper eye protection. Solder paste has flux mixed in though some like to pre-paint the area with extra flux. Malcolm recommends a ‘self-cleaning’ product. Such flux is basically phosphoric acid. This is a good thing when used for its proper purpose, but potentially dangerous. This is the main reason why Wrightscale boilers and burners are supplied ready-made. We wear the gloves and eye protection so that you don’t have to. For obvious reasons, this is Live Steam after all, boilers and burners have to resist high temperatures. For the small but vital jobs – quartering the driving wheels and setting the valve events, a quality engineering retainer such as Loctite 601 is used. It requires a short period to ‘cure’ and so the timings and events should be checked before it has cured ie set firm and I mean firm! Other ‘glues’ and sealants used in making the Wren include instant silicon gasket – Malcolm recommends the Haematite product. This is vital for holding the valve chest and is applied in a 3mm band to the top edge. The valve chest top is lowered on and screwed into place; tight enough to get a small ooze of sealant. Over-tightening the screws means that sealant goes everywhere except where it is needed.

View of the Wren locomotive from the back, photo Malcolm Wright. Rather similar observations apply to the exhaust sealant. This is used where the steam-pipe goes through the burner flue and also to seal the back of the burner. This stops leaks and controls the air supply to the burner.