Leaderboard

The Brede tramway only had one locomotive, a pony substituted for it when the locomotive was out of service for maintenance or other reasons. So I envisaged only having one locomotive in this project too. There were two obvious choices. One was to build a small Bagnall loco like the one actually used on the Brede tramway, the other was to build a model of the small Hunslets used at Deptford by the War Department and later sold to the Sand Hutton line in Yorkshire. I had better documentation in the form of drawings and photos of the Hunslets but the Bagnall design won out because I had a kit of one, albeit for a 2' gauge line and to 7mm scale. This kit was designed and produced by Roy Link in the 1980s, and was, I believe, still available from Narrow Planet until fairly recently I really wanted to model a 18" gauge line though, and I also wanted to model in a scale larger than 7mm scale. I had made a start on the kit but idly thinking about things and making measurements and comparing them to drawings I came to the conclusion that the kit could be modified to suit both 1:32 scale and an 18" gauge prototype. How well it managed was not apparent until a day or two ago when another rmweb contributor posted a drawing of a Bagnall Sipat class in response to the opening entry in this blog. A little jiggery-pokery in GIMP and I was able to produce a drawing where the outline of the Link kit was superimposed onto the Sipat drawing. The chassis is pretty much spot on and while some bits of the superstructure need remaking to a larger scale, a lot is re-usable. I also wanted to try radio control. One of the issues I have with models of narrow gauge and light railway prototypes is the shiny rails needed for good electrical contact. Track also has to be well made because electrical continuity is the first thing to suffer with uneven track. Compensated chassis aren't quite so badly affected but a rigid four wheel chassis will stutter as a result of poor continuity long before anything falls off the rails. I thought that having a battery powered loco controlled by radio would mean rusty and uneven rails would be a possibility. The technology to do that is now available and not that expensive. Lithium-Polymer (Li-Po) batteries pack a lot of punch for their size - rather a lot of punch if you see some of the YouTube videos of these exploding. However in those horror cases it would appear the disaster factors were the fact they were big power-packs to drive aerial drones and they were being abused by fast charging procedures. Small 3v Li-Pos didn't seem to be so scary. A 3v battery implies a 3 volt motor. These are now easily available in the form of the N20 motors used in all sorts of devices. These Chinese motors have the reduction gearing in the form of tiny spur gears rather than a worm which means they have a good bit of torque despite the low voltage. A fellow 3mm Society member, Geoff Helliwell, has done a lot of work on developing motor bogies and locomotive mechanisms in 3mm scale using this motor type, albeit the 12v version, and I was able to draw on his work. The motor itself fitted where a standard 12v motor was meant to go, thus pointing itself up into the firebox Obviously a worm wheel was now out of the question - unless I wanted ultraslow running - but the Helliwell concept uses a crown and pinion arrangement. An idler gear was needed to offset the motor, else it wouldn't go into the firebox of the superstructure. The arrangement was tested using a couple of AA batteries and found to give an acceptable top speed and enough oomph to pull some wagons. I'm now at the stage where I really need to commit to finishing the valve gear in order to finish the chassis, and I have to admit, that is a little bit of a scary thing given the motion doesn't have a lot of waggle room.

I've gradually been adding the remaining smaller details, which seems to take up a lot of time. This first photo shows those at the front end. The lamp on top of the smokebox was included as a "fold-up" job on the etch (similar to a typical 2mm axlebox). The handle is rather delicate and hasn't survived the process of soldering it together, but I don't think you can see it well anyway. I will make the lens using PVA glue after painting. The smokebox door handles are made from etched handrail knobs, while the smokebox hinge is made from some bits of scrap nickel silver. The "taps" beneath the smokebox are a bit over-scale, but this was as small as I could get them, again from bits of nickel silver (the handles are 0.2mm wire). The vacuum pipe is bent up from 0.5mm annealed copper wire as I couldn't get a sharp enough bend in the equivalent width of brass wire. Following Pete Wright's article in the 2mm Magazine (reprinted in the Loco Bits and Pieces booklet), I soldered on thin fuse wire collars at the top, and just used solder to represent the thicker iron section at the top. The coupling hook is a spare from a wagon etch as I forgot to include any on my etch for this loco. All of these bits were soldered on - easier said than done as they are rather fiddly! The vacuum pipe at the rear of the tender is made in a similar manner, as seen below (apologies for the large water droplet on the side of the tender - this was taken after washing ready for painting). I must now make the missing vacuum pipes for all of my other stock! Here you can also see the tender handrails, made from 0.2mm nickel silver wire and etched handrail knobs. With these, solder is used to make them round. This next photo shows two attempts at making some of the boiler pipework. The left-hand one was the first attempt, but was deemed far too big and I reduced the diameter of each of the bits. This is really getting into the realms of approximate representation! These are glued in place under the boiler using Araldite, as I figured I had zero chance whatsoever of soldering them on without the bits of the valve all coming loose. You can see the pipework in place in this next photo, along with most of the remaining bits. The loco handrails are again made from 0.2mm nickel silver wire and etched handrail knobs. The main handrail is all one piece, with 9 knobs to fit at once. It is soldered where I could get at it from the inside, with the remaining knobs glued into their holes. The rather ugly but characteristic feed pipes on the firebox were made from brass wire with little fuse wire collars to try to represent the fittings at the top. The whistle was a brass turning made in the mini-drill using files and multiple attempts. One or two tries would probably have done it except it took me some time to realise that the reason it kept falling apart was that I was using brass tube rather than solid rod! The valves in the top of the dome are simply brass tube with the tops flared out using a drill bit. They were an absolute pig to solder on straight. In this view you can also see the sandbox lids. Presumably they were circular on the real thing but I had to cut away quite a lot of the rear to get them to fit against the smokebox. I'm not sure whether I etched the holes too far back or what. At this point, the loco and tender are ready for the paint shop. I think I will apply a coat of primer and then see if there is any more filling work needed. More lamps are needed on the loco roof and tender, but I haven't etched one of the correct pattern - they should have both forward and backward lenses, I think, and the lamp iron slots on to the side rather than up inside. There is one glaring omission: the cab interior. I didn't include this on the etch (no idea why not), so I will have to cobble something together as it is pretty conspicuous. But I figure it will be better to fit this after painting anyway. One more detail that I have made but will fit after painting is the tablet catcher to go on the cab side. The photo below shows one as etched and another one assembled, before cutting the rod to length. It's not a particularly accurate model, but again its small and will be blackened so will hopefully be good enough.

Adding some details After a rather intensive period of model building, I’ve slowed down a little, while other activities have called for my attention. The train of early Broad Gauge vehicles, including the Posting Carriage etc. still raise a smile as I pass by them on their shelf. They are, however, still waiting for their engine, so I need to press on with my ‘Fire Fly’ class model. my three recent GWR Broad Gauge models I always find that momentum is easily lost, once the main structures have been completed and several major design problems have been overcome. Nevertheless, there are still several tricky areas, such as the brackets that support the boiler, smokebox and firebox above the outside frames. Some of these small parts need as much design effort, or more, as the larger items. I decided to make a list of parts that I would construct as my next objective, to provide a focus for the next phase of this build. For the body, my list includes: support brackets for the boiler chimney and safety valve cover front buffer beam and buffers For the chassis, there are the wheels and inside motion. These items should create the overall appearance of the engine, leaving various small items, such as water feed pipes, handrails, and controls to be added. In this post, I shall cover the ‘body’ items and leave the chassis for next time. Support Brackets When I started to think about the brackets, I was by no means sure that my 3D-printer would be able to create these rather delicate structures, which is what they become at 4mm scale. I found a couple of drawings, shown below, that provided the details of these brackets. I have used these as the basis of my designs. The brackets at the smokebox and firebox sides are similar to one another but different from the central brackets that support the boiler. Fire Fly Brackets – (left) Firebox and Smokebox, (right) Boiler support I decided to start with the end brackets, as I felt these were potentially easier to create. I had already marked the positions on the sides of the smokebox and firebox, to provide reference points for attachment of these items. I brought up a front view of my 3D model of the smokebox in ‘Fusion 360’ and drew the bracket lines and circles with reference to the main model. After drawing the cross section of the bracket, I used the ‘push/pull’ tool in ‘Fusion 360’ to create a solid object. My test print showed that they could be reproduced very effectively by my ‘Geeetech E180’ printer, despite their very small size, as shown in the following photos. Incidentally, the set of four brackets took only 5 minutes to print and they were ready for immediate use – no post-processing was required. My 3D-printed Brackets as printed and then attached to the Smokebox The design of the central boiler brackets presented another challenge in that, on the prototype, they provide direct support to the boiler itself and, therefore pass through the cladding. This can be seen in my photograph of the Fire Fly replica at Didcot, below: Fire Fly replica I decided not to attempt threading my model bracket through the cladding but to truncate the design at the outer surface, I did, however, decide to show the plate at the top of the main strut, as this is how it appears in my reference photo of ‘Argus’. My 3D printed Boiler Bracket (attached to cladding) Chimney and Safety Valve Cover I 3D-printed both these items, using the methods I have described in previous posts: For details of how I created the chimney see this post: For details of how I used the ‘revolve’ tool for safety valve covers (and domes) see this post: As I build more models, I find I can draw on previous designs to solve many problems and I frequently refer back to my earlier posts as aides memoires. Front Buffer Beam The font buffer beam is a simple rectangular bar from which I extruded two cylinders to represent the leather buffers of the period. Assembly of my Fire-Fly class ‘body’ Adding these details to the main components of the body was straight-forward. I used 'superglue' to attach the brackets into the prepared recesses on the sides of smokebox, boiler, and firebox. I had been concerned that the contact area might be too small for successful bonding but, in fact, after allowing time for the glue to polymerise, they proved to be very firmly attached indeed. I provided the bases of the chimney and safety valve cover with spigots, which fitted into holes provided for them. For attaching the buffer beam, I used my tried and tested method of running a low temperature (200°C) soldering iron tip along the inside joins, to weld the parts together. The model shown below has a good solid 'feel', contributed by the brass tube that forms the boiler underneath the cladding. my model of a Fire Fly class engine Computer Visualisation To help visualisation of the planned end result, I colourised the various parts I have made so far on the computer screen. Such views provide plenty of inspiration to keep me going 3D computer model of the Fire-Fly class body Mike

I've made a lot of progress with the Ruston over the weekend. I decided to build the locomotive using 'split axles' for the pick-ups.I decide to try something new here and use the delrin gear as the space to keep the two parts of the axle aligned. The gears are about 8mm wide so each end of the axle is pushed into the gear by about 4mm. A little circle punched from a piece of thin paper is enough to keep the ends electrically separate and the whole lot is flooded with loctite so hopefully it won't move. You can also see in this picture the shorting strips on the wheels which are from Brassmasters. I know the wheels are really too 'thin' for 16mm but having fitted all the rest of the stock with O gauge profile wheels, and built the point work on Fen End Pit to the same standards I have to stick with it really. Firstly I tried running the loco up and down just on DC power. I had to take a fibre glass brush to the wheel treads to remove most of the chemical blackening but after doing this it ran up and down. I benefits from some added weight but there is plenty of room for added lead later. Yesterday was spend in the not very photogenic activity of trying to fit the DCC chips, sound chip, stay-alive capacitor and speaker. The cab has a useful space, formed of a large ballast weight and a locker which gives a useful space for the chips. The speaker is set under the bonnet. The results can be judged in this youtube clip Today I've been adding more etched bits and some more details in plasticard. I also annealed and bent up the tractor seat, which I'm rather pleased with. Next up I have a load of work on the cab interior to do. David