Smokebox dimensions

Have been working out dimensions for the chimney liner and blastpipe/blower arrangement. If you stick to the 1 in 3 and 1 in 6 rules (see JvR's diagram above) it presents a challenge with such a short protrusion of the chimney over the top of the smokebox. With a 13mm ID liner (i.e. a bit of radiator pipe!) you end up with needing to put the exhaust jet underneath the smokebox which clearly isn't practical. Lining the inside of the chimney to 10mm means that you can just about get the exhaust into the smokebox as it can sit 60mm below the top edge of the chimney. I might ask a friend with a G1MRC Britannia how it works on their one as they all seem to steam very well. Perhaps it uses some kind of multiple-jet arrangement? Once I have this sorted I can get cracking with building a proper smokebox and try the boiler on the blower.

Boiler & Burner Test

Enjoyed a nice Sunday lunch and then made up a temporary smokebox with a piece of pipe silver soldered to a flat piece of brass to cap the end. Stuffed the gaps with sheet insulation material to 'seal' it as best i could. Fired it up and despite most (not all, but nearly) of the fittings leaking profusely, the boiler itself was water-tight and the first safety valve lifted off at about 50psi. I have both a large pop valve and an Accucraft valve fitted at present. Pleased with the test and delighted the boiler makes steam ok. Next job - get the chassis running!

Boiler Fittings

Have spent some time on the boiler/burner system recently, hoping to test that it can work effectively in a Stephenson's configuration, with a draught from the exhaust/blower required. The burner is a similar design to the G1MRA Dee design, scaled-up with an additional 'up-comer' for secondary air.

Having tested the burner in an open space I have now moved on to fitting the boiler so that it can be tested. I have had to re-tap some of the bushes as they were all 7/32" with 40TPI threads which made it difficult to fit 'off the shelf' components.

I found that Reeves do a nice clack valve with a  7/32” 40TPI thread so I have bought that and fitted to the boiler. I have also run a 5.5mm drill through the bushings for the water gauge and the pressure gauge and successfully re-tapped these to ¼” 40TPI and fitted the pressure gauge and just need to cut the glass for the water gauge then that can be fitted too. Next job is to turn two adapters so I can fit Accucraft safety valves (these have a metric 5mm fine thread). I am also making a steam manifold to screw into the one remaining bush so that I can then fit a blower and regulator.

Will have to flush the boiler after all that tapping as I am sure it will be full of bits of bronze...