The Coalbrookdale Locomotive

Having a 1/8 scale American locomotive operating, an engine I enjoy very much, and a 1/8 scale Winnipeg Electric Company streetcar well along in construction I was considering what I might model next. Having a keen interest in the history of steam I considered Robert Stephenson's Rocket but even in 7.5" gauge Rocket would be severely lacking in traction and I was hoping to model in a smaller scale (1" to the foot), something that would run on the club's elevated tract and be easier on the back then being constantly bent over while running.

I next looked at Stephenson's "Locomotion", a very unique engine of 1925.

But, if I was going "back in time", why not go back to the beginning? That would be the Coalbrookdale locomotive!

Between 1802 and 1804 Richard Trevithick of Shropshire (England) developed the first practical railway locomotive in the English-speaking world as a motive power for hauling coal on tramways which were previously served by horse power (the 4-footed kind).

The first locomotive developed by Trevithick was the Coalbrookdale, named for the village in which it was built. Virtually nothing was recorded by history, except for a drawing reportedly created by his son many years later, and it is uncertain whether the Coalbrookdale locomotive actually ran or, if it did, what the results of the test were. Considering Trevithick's earlier and later developments, the Coalbrookdale locomotive was in keeping with his personal style and techniques so it is likely that any failings were not the result of the locomotive design. In 1989/90 a working replica of the Coalbrookdale locomotive was constructed and still runs at the Ironbridge Gorge Museum in Shropshire.

I began collecting information about Trevithick's first engine and with the help of some very nice Model Engineers in the U.K. I obtained a series of well-detailed photographs and the Ironbridge Museum kindly sent me copies of a couple of sheets of plans used to build the replica engine so I was off and running. The first job was to draft everything to scale in AutoCAD and work out the design of the boiler. Eventually a satisfactory design was arrived at, one that would meet the requirements for steam and be totally safe operating at 100 PSI. Then design turned to the running gear and other mechanical details of the locomotive.

Meanwhile, having material on hand, the boiler was begun with the barrel and end caps, the 'first chips' for the new engine.

I screwed up the first set of end plates by mis-measuring and drilling two of the tube holes too close together so I did a re-design using one-piece end plates with a circular groove to recess the barrel into the end plates.

The layout of the end plates from AutoCAD was plotted full size, checked for accuracy, and glued to one of the copper plates. Three holes were drill and tapped for registration screws and then the sawn edges were cleaned up on the mill.

All the hole centres were transferred to the copper with a centre punch and all the pilot holes were drilled through both plates before separating the plates and de-burring the holes.

The plates were individually mounted on the faceplate, centred, and then the recess was machined to accept the boiler barrel.


Another COLD day in Manitoba, -30C with a windchill to -40 but the shop is comfortable once the wood stove starts giving heat.

Decided to go ahead with drilling and reaming the holes for the 4 tubes and assembling the boiler temporarily to get an accurate length for the tubes. 


The tubes were turned to length and chamfered on the lathe and temporarily installed in the boiler.


I didn't have a drill big enough (1-5/8") for the flue holes so I bored them and cut the combustion flue.



There were two holes to go in  the boiler barrel, the largest,  1-1/8" diameter for the dome but I  don't have 1 -1/8" bit so I used a large old plumber's reamer to enlarge the hole from 1" to 1-1/8" and that finished the parts needed before silver soldering.


Now if my rotary table would just show up I could round the top of the end plates, solder, and do the initial hydrostatic test .......

I got tired of waiting for the rotary table so decided to cut the radius by hand with a pivot and a lever.

With the radii cut, it was on to silver soldering the boiler. A 10,000 BTU propane hot plate helped provide heat to aid the oxy-acetylene torch and the first joint was completed with full penetration and a nice inside fillet.

The boiler was completed, then pickled (cleaned in an acid bath)


The next step will be installing the tubes and then performing a hydrostatic test.

The smaller tubes were installed and expanded into the flue sheet but I didn't have any way to expand the larger flue so I used soft solder to caulk the tubes in place.


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