Further progress on the boiler. Alas, no more vacation, but some work could still be done over the weekends.
Finding the correct position for the girder plates (also known as crown stays). By adjusting their placement outward or inward, the height of the inner firebox relative to the outer shell can be modified. The central crown stay, positioned in the middle, serves as the reference plane.
I've designed the boiler with a height of 43 mm between the two, measured at the center.
At the same time, care must be taken to ensure that the firebox is positioned centrally within the boiler. The known dimension for this is 8 mm, so two strips, each 8 mm thick, are used to hold the assembly together.
A final check from the smokebox side.
Once everything is in place, the girders are drilled and riveted.
Silver soldering requires more focused heat. Therefore, in addition to the propane torch, an oxy-acetylene set was used. The firebox doorplate was soldered during the same operation. We began with the girders on top and worked our way down to the firebox doorplate. In this position, both could be soldered without the need to move anything.
Cleaning up in the pickle bath.
After cleaning, a visual inspection is done to ensure everything is in order. If not, reheating and resoldering can be performed—this step is easy now but impossible later.
The shaping machine was put to use for making the firebox foundation ring parts
The strip we used was wide enough to use it to wrap around the corners.
It requires some extra machining to achieve this design, but corners are usually a common source of leakage. This approach makes soldering much easier, and the seam can be checked before soldering the rest.
The foundation ring is complete. A small step (recess) was added to simplify the positioning of the long sides.
A recess has also been milled for the blowdown bush, ensuring that the center of the blowdown valve aligns with the bottom of the foundation ring. This allows the boiler to be fully blown down after a run, preventing any water or dirt from remaining inside.
The inner and outer sections of the boiler.
Holes have been drilled in the backhead for the regulator bush, water gauge, and other fittings.
Roughening the backhead girder surface before riveting ensures that the silver solder flows properly between the riveted seam.
Again, the visual inspection confirms that the silver solder has fully penetrated the seam.
After soldering, the bushes for the water gauge and regulator are drilled and tapped. A small steel rod serves as a guide for the tap. This process is done manually to ensure maximum control while tapping with the small M2 tap—I definitely don't want to break a tap here!
Determining the recess that needs to be filed away to create space for the top bushes.
In Solidwork an easy cut-extrude command; here a lot of work.
Drilling holes for 3mm rivets, which will secure the firebox, foundation ring, and outer boiler in place during soldering.
Once again, the surface is roughened to ensure proper penetration of the silver solder.
A simple soldering setup ensures maximum control of the heat. One propane burner and the oxy-acetylene burner are used, allowing precise monitoring throughout the soldering process.
The two boilers are a step further in construction.
Chain drilling the fire door hole in the backkead.
Through repeated filing and measuring, the hole's position is precisely aligned with the boiler assembly. In this boiler, the fire door location is 0.3 mm off-center—not a significant issue and difficult to avoid in this type of metal sheet work. However, the hole in the backhead must be precise, as a soldering seam with a 0.3 mm gap is quite large for silver soldering. A fire door that is 0.3 mm off-center is barely noticeable and functions perfectly fine.
Test-fitting the backhead. To maximize the firebox length, only a few millimeters of space have been left between the back of the boiler and the hornblocks. As a result, the boiler must be manufactured to precise tolerances.
A view of the future cab.
There's still a long way to go, but another step forward has been taken.