I’m in the process of making two fireboxes for the vertical boiler. One for methylated spirit and the other for coal. I know, why? I nearly title this article “Two Fireboxes Nigel”, but not sure many will remember the “two Jags” nickname of a former British Minsiter!
In all honesty I just wanted to have a play and see. This way I can learn about firing with coal and see how hard it is with a tiny boiler. The boiler with the firebox and chimney is just 105mm tall (~4 inches). Air, coal mass, thermal mass, air draft etc is all going to be an issue. I will go through this and share my pains.
The original firebox design was around me using methylated spirits as the fuel. Hence a small firebox.
However, I soon found an issue. The piece of steel I made the firebox from was a bit small in diameter. Thus when firing with meths I singed the wood cladding. I then added the “eyebrow” over the opening to reduce the heat directly on the bottom edge of the cladding.
For the second coal firebox I started with a larger diameter piece of steel. This better matches the diameter of the boiler with the cladding.
For this I need an area for the fire, a grate, an area underneath for the ashes, air holes and doors.
This is quite a lot of detail for such a tiny item. Although a distraction from the traction engine it is always fun to learn new skills.
The fire grate is only 42mm in diameter and was great fun just to think about how to make. Making it was great, although a tad scary.
The scary bit was clamping it after machining one side. However, I made an aluminium jig for the grate machining and this worked very well.
The coal firebox now has two apertures for the fire door and the ash pan.
It also has a step internally that the fire grate stands on.
I now need to finish off the two fireboxes and prove they work.