Edward Adams's 2½" Gauge 'Monstrous'
Well. I've finally made a start on the boiler.
I cut the piece of copper tube for the barrel to length leaving an allowance for final shaping of the firebox end when the throatplate is fitted. There is little else to do to the barrel apart from drilling two holes for boiler bushes and a larger hole for the steam dome bush. There is a fitting on the righthand side of the barrel for the pivot for the regulator operating rods but I haven't quite decided how I'm going to attach that yet. On the old boiler the fitting just screwed into the barrel but I want something better than that.
To do the drilling I set the barrel up on two large Vee blocks on the mill table and then lightly clamped it at each end. To avoid distorting the tube I found that one of the threaded rods from the mill clamp set with a tee nut on each end was just the right length to go inside the tube and support it where it was clamped. That was a stroke of luck!
The holes were then drilled using step drills. These are ideal for cutting holes in tubes as they don't snatch and wander like an ordinary drill would. I've also used centre drills in the past which also work well.
The angle plate and cable tie were added to give more support to the tube after I had cut the first two smaller holes. When I went up to the large step drill the top of the barrel wobbled about without the extra support.
The hole for the steam dome bush needed to be 1.5 inches in diameter but the largest step drill only went up to 32mm. This was an ideal job for my new boring head which I hadn't used yet.
The vertex boring head is a nice piece of kit but the carbide boring tools that came with it are pretty crap. I managed to use the best of them to do the job but I would have been better with a HSS one. The kit does come with two boring bars designed to take a piece of 0.25 inch square tool steel but I didn't have a ready ground piece to hand but I didn't feel like grinding one up at the time. Copper is pretty awful stuff to machine at the best of times but it's worse when you don't use the best tools for the job! Anyway, it got the job done.
I was browsing Ebay earlier and came across a couple of Sievert Cyclone burners for sale at a very reasonable price so I bought them. I've got all the other burners but not the cyclone. They should make soldering inside the firebox a lot easier.
To be continued