16mm Projects

The Welsh Pony as restored in 2020 by Jack Hartwell

After my interest in 16mm scale modelling was revived in 2020 I eventually reached a stage where I had more rolling stock than my Roundhouse Charles could manage. I decided I needed another loco. Eventually after looking to purchase a loco, I decided I would build one. Around this time the Ffestiniog Railways most recent rebuild, Welsh Pony was nearing completion.

Having had a keen interest in the Ffestiniog Railway for many years I decided to build a model of the loco in its current form and livery. I had not built a loco before but had some experience with model engineering. My course at university meant I had access to the latest edition of CAD software’s and so over the next 6 months I designed the loco that I would eventually build. I did not have access to any drawings that were available at the time, so a software program called GIMP was used to calculate dimensions from pictures, as well as a 7mm scale drawing of Prince. The 3D CAD model then enabled me to produce 2D drawing for laser cut parts to be produced, greatly speeding up the build. It had to be worked on only in the holidays or the occasional weekends. As I did not have access to our shed workshop all the time, any processes that would bring me closer to a finished loco were used. I wanted, however, to machine as many of the parts as possible myself. Later my 3D CAD abilities improved, and I was able to have castings produced from 3D printed patterns, for the tank filler, whistle manifold and steam dome.

I decided to start with the wheels and build a rolling chassis. The wheels are machined out of mild steel with the radial slots machined on a rotary table. The cranks are soldered on and make the machining process simpler, once painted it is impossible to notice. The wheel treads were all machined in the same set up with a tool ground to the profile, this ensures they are all the same running diameter and profile. The cranks pins are 1/8’’ stainless steel bonded into the wheels, with a 10 BA thread on the end. A 10BA nut and washer then retains the rods. A wheel quartering jig was made, and the wheels were bonded to the axles with Loctite 603, this method requires you to have a bond gap and the size of this gap effects the strength of the bond. Data can be found on the Henkel website for recommended bond gap sizing. The bond is extremely strong and able to withstand temperatures up to 150 degrees. However, cleanliness of the two joining parts is very important for a successful bond.

Laser cut frames, Wheel sets and cylinder blocks mounted to the frames.

The next job was to machine the cylinders. After machining a brass block to the correct overall dimensions, the blocks were then drilled out and reamed to final size. They were then mounted to a mandrel for subsequent machining. This allowed me to machine the radius, angled side and cylinder end cap bolt holes on the rotary table on the mill. At the time I never got around to polishing or lapping the cylinder bores, however, the finished loco runs extremely smoothly. The inlet steam flows directly downwards from the port face then outwards through the frames to the cylinder blocks where the ports flow diagonally to the ends of the cylinders. This means that there needs to be a good seal between the cylinder blocks, frames and port block. This is achieved by counter boring holes to seat O rings and using high temperature silicone to create a gasket. The exhaust steam follows the same route in reverse but flows directly out the bottom of the port block into a manifold. A piece of 1/8’’ copper tube then passes back past the valve rods and into the back of the smokebox to be directed up the chimney.

Cylinder blocks profiled to the correct shape, and ports machined, valve chest and completed wheelsets.

Next, I completed the valve gear and cylinder assemblies. The loco has a common steam chest, and the valve gear is a simplified single eccentric valve gear like you would find on most Roundhouse locos. I had chosen this because I did not like the thought of making and timing 4 eccentrics for the prototypical Allan straight link valve gear, which is relatively unique to England locos. The valve gear is a robust and straight forward valve gear in terms of design, manufacture and set up of the valves. It performs well with no lap and lead designed into the valve and unlike slip eccentric valve gear allows the loco to be reversed at any time.

Completed rods with bronze bushes, chassis nearing complete and the completed chassis ready to test on air.

At this point we were approaching Christmas 2022 meaning I had more time to work on the loco. The boiler was designed to be as simple to construct as possible. This meant a Roundhouse gas burner and regulator valve were modified for use and the boiler was constructed from 2’’ copper tube with a ¾’’ flue. This is common among 16mm locos so I knew this would work. I added a water gauge to the boiler, I have since found it not to be totally reliable despite trying the usual tricks. So, I top the boiler up with water regularly when running. The boiler was constructed from copper and phosphor bronze was used for bushes with a brass block soldered to the underside of the boiler for mounting securely to the footplate. The boiler was soldered up in December 2022 by myself and my father. It is very useful having a spare pair of hands and eyes when soldering boilers. For anyone designing a boiler I would suggest having the largest opening to the gauge glass fittings possible, the bushes I used are 3/16 X 40ME and the hole is 1/16’’, this is too small to provide a reliable reading on the gauge.

The boiler before soldering, completed boiler ready for hydraulic testing and the boiler mounted to the chassis and frames assembly.

I added stays to the gas tank which double as bushes for bolting the tank to the underside of the footplate. Following successful hydraulic tests by Rodger Schofield, I gave the loco a steam test. There were some small issues such as the gas burner whistling, I later discovered this was due to the gap between the flue and smokebox, and adding the bodywork closed this gap and solved the issue. Nevertheless, mechanically, the loco ran flawlessly. This was very encouraging and now I could work towards completing the loco.

The Gas tank showing the stays which help to strengthen the gas tank when it is under pressure, the completed gas tank ready for testing. The loco following hydraulic testing of the gas tank and boiler and a steam test at the Yorkshire groups New Year steam up.

The body work was largely constructed from 0.5mm brass sheet and the outer frames and footplates were constructed from 1.5mm brass sheet. A lot of the parts were laser cut and produced to my drawings. Rivets were added using a Model Engineers Laser rivet embosser kit and were all marked out and embossed individually. The smoke box assembly was fabricated from brass sheet and some machined parts. It is held down by the sand-pots through a length of 8BA threaded bar which also threads into bosses on the front footplate.

Body work being assembled and starting to look like a loco finally, the smokebox assembly and some cab detailing.

The RC receiver and battery pack is hidden under the tender coal load with the switch accessed from underneath. The RC servos are Hi-Tech HS5055MG servos, and they are hidden out of the way as much as possible. The loco now had several steam tests to make sure everything worked, and issues were resolved as they arose. Once I was happy with the loco in steam, I began what ended up as being a long process of detailing the loco. Lots of castings from Slaters’ Prince were adapted for use as Welsh Pony and lots of detailing parts were fabricated to match the prototype.

A Completed loco in the brass.

Painting and lining the loco was the most daunting task for me, I have some experience in both but needed to improve my abilities to be satisfied with the result. For airbrushing I used a relatively cheap Clarke airbrush. This was a good airbrush, and it did produce an excellent finish so I can recommend this airbrush to anyone looking to have a go.  However, I did not realise the rubber seals used are not suitable when cleaning the airbrush with cellulose thinners. Part way through painting the cab some of these seals were propelled onto the surface. I then stripped the cab to bare metal and purchased a Badger crescendo 175 airbrush, this was a considerable investment for me but was worth the cost. The cab painting and all varnishing was completed with this air brush.

Painted components and a mock-up of a lot of the parts after painting.

Onto the lining; the first step for most of the parts was to create the black border. This was done using a bow compass with the pointed tip replaced with a rounded of piece of brass rod. This means the spacing can be easily adjusted for adding the orange lines. I made Plasti-kard templates, held onto the body work with small pieces of Blu Tack wherever possible. For example, the straw corners were each produced with the same template ensuring they are all identical. The piece of advice I found most useful for lining was to walk away when you are happy. The worst thing you can do is try to do too much. You can easily remove the fresh bits with white spirit on a brush. However, if you need several attempts to join two straights at a corner you want to make sure you can’t wipe the straights off unintentionally. Sticking to this advice I gave each colour 12 to 24 hours before attempting the next stage. A mixture of bow pens and lining pens were used as well as various paint brushes. A great source of knowledge is Ian Rathbone’s book on the subject which covers everything to do with painting and lining a locomotive.

A step by step of lining the tender, it is broken up into much more stages, but this provides an idea of the steps that worked for me. The same process was repeated for each panel.

The loco was then varnished which was even more daunting than the initial painting. I feel this step is necessary in this instance because I had used transfers on some panels and the varnish provides a high gloss protective finish ensuring the loco looks good for years to come. The most important thing when painting is cleanliness. The work area, the work piece and you all being clean ensure you limit the risk of debris in the paint and issues with paint adhering. I used lint free cloths with acetone to clean bare metal and panel wipe for painted parts. Good extraction and a high-quality spraying mask also make the process much more bearable and of course they prevent any damage to your health. Once the paint and varnish had a few days to dry and harden I began reassembling the loco, trying hard not to scratch anything!

The completed lining now protected under varnish. The assembled chassis and loco excluding the bodywork.

Finally, the loco was fully assembled in August 2023 and given its first run. It performed very well, and the only fault was a leaking gauge glass gland which was easily solved once identified. The runtime is approximately half an hour with a heavy load, and the water usage is quite low. Now it is finished I can say I thoroughly enjoyed the build process and I look forward to the next project. Post completion I have also added a whistle to the loco which adds a bit of fun when running. Thank you to all of those who helped with advice and ideas along the way.

The assembled and completed loco.


October 2023



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