16MM PROJECTS

JAMES MEDD : The Exmoor project

Building Exmoor Steam Railway locomotive 325

The Exmoor Steam Railway isn’t particularly well known as a builder of narrow gauge steam locomotives. Names like Hunslet, Kerr Stuart and Fowler might be more recognisable to those in our hobby, but Exmoor, who are based near Bratton Fleming in Devon, are possibly the largest supplier of new steam locomotives at present. Since the early 1990s, they have designed and built a number of attractive locomotives in gauges ranging from 7¼” to 15”. They are also involved in preserving larger engines, and in 2006, they restored one of the Beyer-Peacock Garratt locomotives for the Welsh Highland Railway.

The Prototype

Number 325 was built in 2009 to a design which shares some characteristcs with the South African NG6 locomotives. It is a 2-6-2 tender engine fitted with Walschaerts valve gear and painted in black livery with white and red lining. Originally designed for the 12¼” gauge Exmoor Steam Railway, it later spent some time at the Exbury Gardens Railway in Hampshire which already owned two Exmoor-built tank engines. Ultimately, a second engine to the same design was commissioned by Exbury; painted in their standard royal blue livery and carrying works number 326, it was named ‘Mariloo’.

Number 325, which later received the name ‘Black Beauty’, was transferred to a safari park railway in Denmark, where it remains now. The prototype is not a narrow gauge loco in the traditional sense, as it runs on a track gauge of less than 2’. However, as the design and aesthetics of the loco appealed to me, I decided to build a model of it.

The Model Construction began with a standard Roundhouse ‘Fowler’ chassis kit, which was assembled over the course of several weeks. I used M3 hex-head screws instead of machine screws and painted the wheel centres black, removing excess paint on the lathe. Roundhouse crossheads and union links were fitted to the cylinders as well. The frames were spray painted in satin black and the cranks were painted in Humbrol tank grey. Once complete, the chassis was run in on compressed air and all seemed well.

After fitting the smokebox, the next major component was the boiler. I decided not to use a standard ‘Fowler’ boiler, so I designed a custom one which allowed me to place the bushes for the steam fittings in the places where I needed them to be. The boiler was fabricated and pressure tested by GB Boilers of Bedworth. As the prototype loco is a 2-6-2, I needed to find a way to attach the mounting bar for the leading wheels to one of the frame spacers. Sadly, after trying out several options, there didn’t seem to be a way to attach the pony truck without it fouling the superheater and exhaust pipes between the frames. I regret not making a custom chassis, as this would have allowed me to position the frame spacers where I needed them, and I could have extended the frames to include the front step and cut-outs for the front pony truck. However, I felt that I didn’t know enough about valve gear to design the chassis from scratch. That’s maybe something for a future project! With the model now designated an 0-6-2, I needed a way to extend the frames forward by about 25mm. The solution was provided by Tom Beattie from Locoworks who made a brass box which attaches to the front of the frames. Tom also made the running boards which sit on either side of the boiler and they attach to the frames with small metal clips.

My attention now turned to the bodywork for the loco, particularly the cab. Unfortunately, I wasn’t able to obtain any drawings of the prototype, so the size for each item had to be determined by finding a suitable photo of the engine, scaling it, and measuring the dimensions from there. I prefer to design components using a CAD program rather than on the drawing board, and as I lack the skill and dexterity to cut and file sheet metal to profile, the cab panels and other items were laser cut. 0.9mm brass was used for most of the parts, with 1.5mm mild steel being used for the cab footplate and tender base. The cab was soldered together with pieces of ¼” brass angle in the corners to support it. This was the first time I’d soldered large items together so it took a bit of practice, but I managed to get neat solder joins after a few attempts. A steady hand, plenty of flux and a 100 watt soldering iron certainly help, but my Dad also made a jig to keep the work square while soldering.

Some of the smaller parts were turned on the lathe, such as the spectacle plates and sandboxes. I don’t have a milling machine, but it was possible to make some components, like the sandbox supports, using a vertical slide attachment and a suitable cutter held in the lathe chuck.

The roof and boiler wrapper, which again are laser-cut parts, were rolled to profile using a set of slip rolls – another skill which takes practice to get right.

With the boiler now in place and the bodywork starting to take shape, it was time to add the steam fittings. The loco is internally fired and uses a standard Roundhouse poker burner and gas tank.

The usual fittings and controls, including the displacement lubricator, regulator and reversing lever were fitted one by one. The boiler has a spare bush fitted so that I can add a water top-up valve in future.The loco was first steamed in April this year, and apart from a slight leak on one of the displacement lubricator pipes, the loco ran smoothly in both directions. After fixing the leak, which just required a little more silver solder, I began to design and build the tender. The tender consists of two standard Roundhouse bogies and a ‘Fowler’ tender casting. A baseplate is bolted on to this, and then the tender panels are attached to a framework of ¼” square brass rods which are drilled and tapped for various fastenings.

The tender is mostly screwed together rather than soldered – I designed it this way so that I can add radio control equipment easily in future. However, I was able to practice soldering a few more small items, such as the coal scuttle.

A coal load was made out of a piece of styrofoam which was cut to shape, given a coat of PVA glue and covered with pieces of model coal.With the loco more or less complete, and after a few more steam tests, it was time to fit the boiler wrapper and bands. I had designed the wrapper with small ‘tags’ that would have been used to secure it to the boiler, but these broke off during rolling. Fortunately, the 3 boiler bands hold it securely in place.The completed loco and tender were put together on the workbench, then the model was dismantled and the parts were cleaned up and prepared for painting.

The parts of the loco were painted black using 2-pack automotive paint, with a gloss finish for the cab, boiler wrapper and tender panels, and satin for the footplate, running boards and many other small items. While the parts were being painted, I took the opportunity to touch up the paint on the chassis which had chipped off in places, and I also painted the smokebox and boiler using heat-resistant paint. The painted items were collected after a few weeks, and the cab and tender components now require lining. I began to rebuild the model by refitting the boiler wrapper and the boiler bands, and this is as far as I’ve got with the project at the moment. The next jobs are to attach the smokebox to the chassis, fit the boiler and add other components in time, and I’ll certainly update this report as the project continues…

Lessons learned – so far!This project has been useful in introducing me to new processes, tools and techniques. Probably one of the key tasks I’ve learned is soldering, using both soft and silver solders. I’ve understood why the work must be clean, how to clamp pieces of work effectively without losing heat, and how different kinds of solder can be used for different jobs depending on the size of the item being worked on. I’ve also had to learn how to use bending rolls, and I’ve continued to use the lathe to produce various components. I wish I’d waited until I’d completed all the bodywork before painting the chassis, because the paint invariably became chipped and flaked off when different items, such as the cab, footplate and running boards were tried in place. I’ve retouched the chassis with satin black paint, but the finish would have been much better if I’d kept the chassis in bare metal until all the other components were completed.

I’ve also recognised the benefit of constructing a model using scaled drawings – sadly, drawings of the prototype were not available, so I had to work from photos to obtain the right dimensions. It would have been much easier to build the loco using dimensions taken from a set of scaled drawings, so that’s definitely a consideration for future projects.

Even so, I hope that what I’ve produced is a reasonable model of the original loco. Finally for now, the old saying ‘measure twice, cut once’ is always a good rule to follow!

James Medd

August 2020

 

G.B. Boiler Services

Eastland Fields Farm

Bedworth

Warwickshire

CV12 9SD

gb.boilers@hotmail.co.uk

 

 

 

 

 

 

 

 

            

     

    

 

 

 

 

     

 

 

  

 

     

 

 

       

 

 

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