Having returned to model engineering after a 33 year break I decided the best way to ease myself back in was to use my newly acquired lathe and mill to build an S50.

The build had its issues, but thanks to Tubal Cain's "Sally" serial in ME we got there.

A boiler was required, but most (all) horizontal boilers off the shelf seemed to be gas or spirit fired and designed for marine applications. I could not find a coal fired model horizontal boiler – either design or finished article – for love nor money.

So having read K.N. Harris's excellent book, I took inspiration from one of his G.A. drawings of a Cornishesque boiler design.

My boiler is now built and tested (by a professional inspector, who approved my design). I would like to share the journey.

It's 6" dia and 13 inches long. I will expand on the detail in my next post…with images.

Hello,

Please forgive the quality of the images, but hopefully will give you an idea.

Making a working scale replica of a Cornish boiler would, given the original design of a centre flue containing the furnace and galloway cross tubes with two exterior side brick return flues and a single exterior flue taking gases under the base of the boiler to a tall chimney, result in a pretty big model – by my calculations it would have been huge. I obviously decided this was completely impractical, so took inspiration from the 'Sweet Pea' style marine boiler and designed it so it could appear as a Cornish boiler and stay within model proportions, suitable for a 1' x 2' bore and stroke engine. My intention is to build the Stuart Victoria next.

The back head is pretty key to giving a sense of authenticity so I did try to model this on a real boiler. (See pictures) You will see that my solution was to put a 3.75 inch diameter firebox inside a 6 inch barrel. The firebox is around 5 inches long and is secured into the back head with silver solder and a riveted staying ring, which accommodates the back head and grate assembly. The back head was machined from a 4" diameter x 1" thick piece of cast iron solid.

There are 16 smoke tubes and the whole boiler is 15 inches long which allows for a 2.5 inch deep smoke box which accommodates a 'steam dryer'. There is a steam blower built into the chimney base, fed from the stem dome.

From the design MSWP is 80psi, so the initial hydraulic test was 160psi for 30 minutes. The boiler is silver soldered throughout – by me. All bushes and the domes are bronze. All materials were sourced from Blackgates, and the cheat was I used pre flanged 5" Springbok smokebox tube plates and the firebox tube plate was supplied flanged. My design and initial drawings were run through a computer model by my boiler inspector. I also own a 4" Scale TE.

The grate is Blackgates 5" gauge stainless section, which I formed to create a basket 3.5" x 4.75" x 1" deep. I have test steamed it on anthracite grains and it steams reasonably well. Well very well once I got the hang of it. If you look at the nearly finished image, you will see the ash from today's steaming.

I bought a 6" Southworth steam pump off a chap in Stamford and made the Stuart hand pump from castings to supply feed water.

Anyway, I can expand in more detail if anyone is interested.

Edited By Driver 92212 on 20/11/2014 20:08:50

Edited By Driver 92212 on 20/11/2014 20:11:47

Steamed the plant today…   http://youtu.be/7RLJJlU4CJU

Happy to answer any questions

Edited By Driver 92212 on 30/11/2014 17:19:55

Having thought about Fizzy's post about feed water I have just ordered materials and fittings from Blackgates to make a feed water heater. The plan is to use the exhaust steam from the duplex boiler feed pump to pre-heat its water output. This should raise the feed water temp to around 80 degrees C once it is up to temp.

It will be a coil indirect type which will double as an oil trap – I will incorporate a drain for the condensate. I might then look at routing the exhaust steam from this up the chimney. One step at a time.