Almost a year ago, we made most of the boiler parts. But problems with milling machine called for a heavy repair that took some time and the boiler was put aside.
With the milling machine repaired, it was put to the test and so we continued with machine work. Now with the loco on its wheels, and a start was made with the tender, we finally continued with the boiler.
To start with this job, we needed a spell of good weather and a long weekend, to get a reasonable amount of work done for a start. I find the process of soldering the boiler the same as painting the loco. Once you start you want to continue, because all the necessary things are set up (acid for etching, fire bricks, burners, etc.) that take up a lot of space in my small workshop.
This first part of the assembly was done in four consecutive days.
The fine weather was needed, because silver soldering the boilers in the workshop isn't possible. It would get too hot inside very quickly.
Since we are making two locomotives, and thus two boilers at the same time, the soldering and preparation of the joints takes more time. However, working together has the advantage of having extra hands to hold the work for drilling and riveting. During soldering, four eyes see more than two, and two propane burners generate more heat.
Still, for a 5" loco, this is a relatively small boiler, weighing only about 10 kg.
An extra ring, made of 3mm copper plate, is added to give strength to the barrel and to keep the dome ring in position during the soldering.
I start with this ring, as this ring is a reference plane for the boiler barrel orientation towards the other parts.
For etching the copper after soldering to remove oxides, we used a PH-reducer for water. This is intended to be used in a swimming pool. By using more than normal doses, the water becomes acid and it works as a good etching fluid.
See this link for the stuff.
After 5 to 10 minutes in the 'bath', the copper changes to a nice pink colour.
The dome ring after cleaning.
The holes in the smokebox tube plate and firebox plate were opened out a bit more, so the fire tubes could be inserted more easily, and silver could get into the joint.
A simple setup for soldering the flues to the firebox plate. The smokebox plate is NOT soldered yet, but only used to keep the flues aligned.
A check of this soldering operation
The solder nicely shows on the other side, so a good joint is made.
Silver solder was only added on one side.
On Toin's boiler the same job for the dome ring.
The inner dome was screwed on the dome ring and clamped in the vice with a V-block. Now the holes in the side of the boiler could be measured out for the clack valves and drilled.
The bushes for these valves were held in position, by two copper pipes, held together with a spring-loaded threaded rod. Because the boiler expands during soldering, the spring would still hold the bushes on their place, without deforming the barrel. If you take a close look, you'll see white ends of the copper tubes; Tippex is applied, preventing silver solder to run there. Otherwise one could mistakenly solder the tubes to the bushes.
Aligning the barrel to the fire box.
The total work, done on the first day.
We noticed two things today: with a burner that is too small, you do get heat, but it takes too long. The flux is then already 'used up,' and the solder does not flow as nicely anymore. With the larger burner, we reached the right temperature more quickly, and the soldering process went much smoother.
Secondly, at the boiler shell, where the dome flange and reinforcement ring are soldered, the total copper thickness is 6 mm, along with the thick bronze dome ring. This requires a lot of heat, because the shell itself absorbs a significant amount of heat. Soldering then becomes more challenging due to the radiant heat from the boiler at soldering temperature, and sometimes the flame heat reflecting back onto the boiler shell. Thick welding gloves are an absolute must.
The second and third day were used for the assembly and soldering of the outer boiler; barrel, firebox and throat plate.
Aligning the boiler barrel to the outer firebox. Pre-drilled holes in the outer firebox wrapper are centred through, once everything is in line.
With M2 screws the parts are hold together, during riveting.
Riveting the parts together. 2 mm copper rivets are used for the job.
Working with two people is a big advantage here, for holding the parts in position on the stake.
The throat plate is clamped in place before drilling the holes for the rivets. Rivets are necessary not only to hold the parts together but also to maintain a tight seam. At soldering temperature (650 degrees), the plates will expand, and without rivets, the seam may widen due to thermal expansion.
Two Sievert burners are needed for soldering these parts.
Doing this outside has the advantage that we will not get too hot and that we can work around the boiler by moving ourselves. My workshop is too small, even for this boiler.
After the job is done, we let the boiler cool down to about 50 to 80 degrees before putting it into the etching bath.
A visual check, while the boiler is still hot, to see if the solder has nicely run through the whole seam.
With a ladle, picked up at a charity shop for 1 euro, the rest of the barrel is cooled down and etched.
Before cleaning the seams (by removing any surplus of solder), a second check is made to see if all the seams are ok. If not, no problem. Reflux, reheat and re-solder.
My boiler on the right is already soldered and cleaned. Toin's boiler on the left has a barrel that is rolled from sheet material. A strip on the top is used to give the seam over the barrel length sufficient strength.
(The boiler design book gives formulas to calculate how thick this strip should be, and how wide the overlap should be.)
A quick job also done on the third day: soldering the firebox ring to the inner firebox back plate. This is a one-man job.
The fourth day was used to rivet and solder the inner firebox wrapper to the tube plate.
The working method is the same as the outer boiler shell, but not as large.
It was soldered in an upright position. The seam is clearly visible this way, allowing for better heat control. Everything is fluxed again; the fire tubes will get hot once more, but must not be unsoldered. Care must be taken to direct the heat of the propane flame to the wrapper, minimizing heat on the tubes.
The boiler shell for a test fit on the frame. The two boilers are both ready thus far.
