In the previous entry, I described my approach to making sandwich frames. While that was only a small part of building a chassis, I decided to change tack and have a look at how the ‘super-structure’ of the Broad Gauge kit goes together. As I have mentioned before, I am considering how the boiler in this BGS kit for the Gooch Standard Goods might be used to create a model of the ‘Waverley’ class 4-4-0.
To put it mildly, the instructions with the kit are somewhat terse in their description of this part of the construction – just three lines: “The boiler is straightforward. Press out all the rivets in the firebox, roll up the boiler (or use tube) and put the smokebox together. Again, these vary depending on the prototype as they were changed over the years.”
Those few words actually cover quite a lot of work! For a start, the firebox has an awful lot of rivets! So, “all the rivets” actually translates into “242 rivets”. Yes, I counted them! When I pressed out the rivets on the frames, I used a centre punch but it was a bit too coarse for the job so, this time, I used an old school compass point, which provided a much crisper result. Since the boiler was half-etched to ‘raise’ the boiler bands, it’s a pity the kit designers hadn’t used the same method for the firebox.
From what I have read, many builders quail at the idea of rolling boilers but this one went quite easily, once I had plucked up courage. The rectangular sheet of brass on the fret is already half-etched, with the boiler bands standing proud, so it’s easy to see which way to start rolling. Because of the half-etch, the sheet is thin and flexible and responds well to being rolled. Also, there are no holes or other obstacles in this sheet, to cause difficulty, and I soon had a round-looking tube.
My method is to place the sheet, outer side downwards, on the back of a mouse-mat, which provides a suitable resilient surface. I then use a steel rod as a rolling pin, gently teasing the brass into a smooth curve while rolling back and forth.
The next step, which, also from what I have read, puts a lot of people off building metal kits, is to solder the seam of the boiler tube. I believe that the key points to understand when soldering are that a good dose of flux along the whole area to be joined is essential and that the iron must supply sufficient heat to produce rapid melting, as soon as the iron touches down. The aim is for the soldering iron to heat up the joint enough for the brass to melt the solder - not the iron. I use phosphoric acid flux at about 10% dilution and a 65w temperature controlled iron, set to a nominal 285°C with 60:40 tin/lead solder. It’s also important to remember that the brass holds the heat for some time after removing the iron, so allow several seconds for the solder to solidify, before moving anything.
In the following paragraphs, I set out a detailed description of how I tackled the various stages of construction. For much of the time, I was ‘feeling my way’ and, quite often, I felt unsure of how to proceed. Fortunately, I managed to get through the various challenges, so I hope that my description will prove helpful and will, perhaps, give some encouragement to others.
I use an elastic band, near the centre of the tube, to hold the cylindrical shape and then concentrate on making sure that one end is aligned correctly, before applying heat briefly to that end to make a firm local joint. I then repeat at the other end, before running the tip of the iron along the inside of the joint, to ensure that the solder runs along the full length of the tube. After the ends have been fixed, I prefer to use my fingers to hold the tube and keep the seam straight, with a wad of tissue to protect my fingers from the heat.
Once satisfied that the joint is firm, I immerse the components in water, to remove any residual flux. I also like to clean up the brass with some toothpaste and an old brush. The end result looked like this:
In the absence of any further guidance from the instructions, I now had to make my own plans for the way ahead. Having pressed out all those rivets on the firebox, I decided to continue working at that end of the boiler. There are several parts, identified in the instructions by the labels shown in the following photo:
As well as the brief instructions, there is also an ‘assembly diagram’ of the boiler, smokebox, and firebox but it gives no indication of where to begin or the order of assembly. After inspecting the various firebox parts, shown above, I decided that the two hoop-shaped items labelled as ‘firebox rings’, which have half-etched detail, are intended as cosmetic overlays for the ends of the firebox. So, I decided to start by fixing the item labelled ‘firebox ring to boiler’ onto the end of the boiler tube. There is a half-etched recess in the ring, which fits over the end of the boiler. After some thought, I placed the ring on top of the boiler tube while it was standing vertically on my soldering mat. I then used a cocktail stick to hold the top of the ring firmly against the boiler, while I applied flux and then made a local soldered joint at this point.
After checking that the alignment looked good, I moved to the bottom side of the boiler and ran the solder around the inside circumference, using the cocktail stick to keep the parts pressed together. I was pleased to find that the parts fitted together very well, with just a narrow fillet of solder appearing on the outside rim of the boiler, as shown below
I now had to decide how to roll the firebox wrapper, which is not a simple shape but needs to fit around the profile of the firebox back. There is no etched detail on this wrapper but there are holes for mounting the safety valve cover and whistles. These openings imply a need for extra care when rolling the wrapper, to avoid any kinks at these points of weakness. Because the wrapper is of thicker brass than the (etched) boiler, it proved more difficult to start forming a smooth curve.
Once I had an amount of curvature that was approaching the profile of the firebox back, I had to decide how to create the complex shape of the firebox sides. The lower sides appear flat, so I marked lines on the wrapper to mark the transitions between the curved top-part and the flat lower-parts. I then folded out the lower-sides at an appropriate angle from the upper part.
Next, I decided to place the firebox end flat on my soldering mat and then held the wrapper with its rear end also against the mat. I then pressed the two parts firmly together, ensuring that the wrapper was tight against the top of the back plate. At this stage, I did not attempt to bring the open ends of the wrapper close together but identified two points, either side of the top, where it was still in good contact with the back. I applied flux and soldered these two points. I then continued to make a continuous seam around the top of the firebox.
Once the top was secured, I used the tips of my pliers to press the wrapper firmly against the profile of the back and started to solder around first one side and then the other. While doing this, I also adjusted the angles of the flat sections to ensure they fitted the lower part of the profile. As with the boiler, I used my fingers to hold the wrapper at critical points, with a wad of tissue for protection. It was essential to work quickly, both to avoid re-melting previously joined regions and to avoid burnt fingers! The end result is shown below:
Now that the shape of the wrapper was defined by the back-plate profile, it was relative easy to attach the firebox assembly to the ring that I had already fitted to the boiler. The only difficulty lay in ensuring that the parts were aligned correctly, before completing the soldering. I started with a local attachment close to the top of the boiler and then worked around the edge of the wrapper, from below, using my fine-nose pliers to keep the firebox sides pressed firmly against the ring.
The end result of this stage is shown below. I was very relieved to find that the folded grate and ash-pan component fitted neatly into the open bottom of the firebox!
I readily admit to having had some difficult moments during this assembly. There may well be better ways of building this part of the kit but, at least, my approach has provided a result that pleases me
Next step will be to look at the smokebox end of the boiler.