Scrap Tank - dome

scrap tank

Entry posted by antyeates1983 July 19, 2020

277 views

I made a start on the boiler "furniture" by making the dome. The first problem I faced was not having an accurate drawing of the real thing. This led to me making a first attempt, looking at it sat on the model, and then doing another one with slightly altered dimensions. Although it took some extra time, this did also mean that I had a practice run to work out my method.

I started with some 8mm brass rod (annoyingly, the widest part of the flange was estimated to be a little more than 6mm, which was the next size down that I had. I started by chucking this in the lathe drilling a 1.5mm hole through the bottom, finishing somewhere midway up. I then reduced most of the extraneous material. For this I used a small semi-circular (home-ground) turning tool - this leaves the bell shape at the bottom. I then turned down the thin spigot at the top, which will eventually be reduced in size to make the small "blob" visible on the top of the real domes. I parted it off with a bit of extra full-diameter (8mm) rod, which you see here in black.

Then I put it in a vice and carefully filed the base to "boiler shape" by hand. I find it useful to start with a triangular file (or even a saw blade) and widen this to get a straight line that is well centred. Then I start with a round needle file, followed by a larger round file, followed finally by some wet and dry wrapped around a spare length of the boiler tube. In this photo you can see the mounting hole in the bottom.

Next stage is to make a temporary mandrel to hold the dome for remaining shaping in the lathe. This was turned down from a length of 6mm brass rod. I make it long enough that I can saw it off when done and let it double as the locating pin for attaching to the boiler.

I left this in the chuck (to maintain concentricity) and attached the dome with cyano. I found that a reasonable amount was necessary to hold it on, but I didn't fancy trying to solder this large a lump of metal in the lathe.

Next you see the use for the spigot at the top: it runs inside a length of brass tube held in the tailstock chuck, to support the piece during subsequent turning.

I then turned the main diameter down to the correct (guessed) size. If this looks different to the previous photo, it's because this one is the initial test version, I think.

The rounded end was then turned by hand with a graver. Here you see a length of tool steel held in the toolpost acting as a rest for the graver. Probably I should make a better one by turning one of these down to circular, but I haven't got around to it.

The final job on the lathe was to turn down the "pip" at the top as much as I dared, using my usual parting tool.

After taking it out of the chuck, I left it on the rod to allow me to hold it during final shaping of the bottom flange. I think there's no option here other than doing it carefully by hand with needle files and wet and dry.