Loco about Locos

Work has progressed - the boiler is now complete. The assembly sequence I used was as described in Alex Farmers book on boiler making - and, as it happens, his was also a GWR boiler, although bigger. As the assembly gets bigger, it always surprises me just how much heat it needs. I work outside, so can only work on wind-free ( and preferably dry) days. Also, I find it essential to use refractory bricks- without them, I'd never get up to temperature. Even so, it needed two good sized gas torches, and occasional oxy-propane, to complete the assembly. I couldn't do this alone, and gratefully thank George and Russell for their help. Where ever possible (and that's most of the time), we worked with pre-placed solder - its much easier than applying a stick, as it tends to melt - or at least sag - if you're not quick. We put rings of silver solder under the heads of all the rivet - stays in the firebox. As the solder flowed, each was grasped on the outside with pliers, rotated

Some of my boiler making tools. I formed the taper barrel using a set of bending rolls. I decieded that the chances of cutting the sheet to exactly the right dimensions was pretty small - the copper stretches when rolled - so I left the sheet oversize, and planned to cut it after forming. I know this makes for less convenient cutting, but at least it wont be short. Just as well; after annealing and rolling, the taper ended up at the opposite end to what I'd planned - it didn't matter one little bit. So once it was almost to shape, I could work out exactly where to cut it. I rechecked the dimensions once I'd got rid of the overlap, and found there was still a little to file off. I drilled the strap and riveted it to one side, pulled the barrel up tight with a strap, and drilled and riveted the other side. Before doing so, all the surfaces were finally cleaned and covered with flux. I laid two strips of (high temperature) silver solder at the centre joint, and added some more

I decided that I didn't want to cut holes in any of the plates until I'd formed the firebox wrappers - so I started on those next. One way to form them is to make a wooden template and beat the annealed copper around them. Or you can form the sheet using bars of the appropriate diameter, which was the way I chose to go ( not being an enthusiastic woodworker !) Once annealed, the copper is incredibly soft, and needs little more than hand pressure to start to form it. I used various formers, as the pictures show. This firebox has a combination of inside and outside curves (most do) which makes it arkward. I just bent a bit at a time, checking against the flanged plates. A good fit is important, as silver solder has no gap filling properties. When the copper stops bending easily, its time to re-anneal. It took me five or six heats to get the inner firebox wrapper to my liking - less for the outer. Incidentally, I deliberately left the sheets oversize; putting lots of bends and f

I know several model engineers who wouldn't touch boiler making - it's not for everyone. You need several sources of heat - a lot of it, somewhere safe to work, and you need to be aware that - unlike most aspects of model engineering, it is possible to get into a situation where all your work - and expensive materials - are irrecoverably scrapped. I've got to say, I like the challenge, and satisfaction that its 'all my own work'. Then there's the lack of waiting time. Whilst its also true that there's a significant cost saving, this is definately not a good reason for doing it. I bought a kit of materials from Reeves- this comprises all the copper sheet, bar and tubes. You really do need to have the correct materials, all in good condition, and, these days, of traceable quality. Copper is interesting to work with. After annealing, its amazingly soft, and can easily be shaped - until it reaches a point where it work hardens. Its then time to stop and re-anne

The frames were already cut out, saving a bit of sawing. I checked that all dimensions were correct, and cut out the buffer beam and drag beam, from angle section. It never seems to be truely square, which shows up on the insides, when the angle fixings are mounted. So i lightly milled them all over, which got rid of the mill scale at the same time. Also the angle sections to lock it all together. I clamped the angle iron in place, and drilled through from the fames. Only then, I marked of the length of these pieces, taking the dimension from the frames rather than from the drawings - at least this way, they all fit accurately. I worked on a surface table, checking that all was square as I went along. For the horn blocks, I milled the mounting surfaces to size, and riveted them to the frames, slightly overlapping the horn openings. then milled the horn gaps to size - if they were milled to size before fitting. This makes sure that the horn slots are accurate and truly square. If I'

I've been trying to buy a panel saw (sheet saw?) for some time, but have been told that they havn't been made for many years. I was lent one a year or two ago, and found it much better for cutting large sheets of brass than the jigsaw I had been using. As I can't just buy one, I took an old wood saw, and ground off the cutting points. I then made up brackets to mount a fine-toothed 12 inch hacksaw blade, and drilled the saw blade to suit (A solid carbide drill goes straight through the saw steel) It might look a bit odd - but it works. Its as easy as can be to cut a straight line right through a 4 ft by 2 ft brass sheet. I might get round to tidying the saw up - the real thing is styled like a tenon saw without the tenon. And there seems to be no need for a blade tensioner because of the way the saw works.

I initially assembled the linkage with all the joints unpinned, so I could check that it all fitted and could move freely without any obstructions. Disaster!!! The angles that some parts of the motion were moving through were clearly wrong. The pendulum levers - which support the expansion link, and the link hangers were both visibly wrong. I checked all the components against the drawings - and discovered that the weighshaft -which supports the link hangers had been located in the wrong place on the frames- a dimension of 13/32 on the drawing had been set out as 13/16 in. (Actually, by the original maker of the frames -but I was supposed to have checked it). Everything else was correct - but -adding up the various dimensions on the drawing showed that the centres for the link hanger brackets were in fact wrong -by 1/8 in. Still, it made me read up and understand how Stephenson link gear is designed. To make matters worse, I'd drilled all the mounting holes around both items,and th

The Hall uses Stephenson link gear mounted internally between the frames, and the cylinders have piston valves. Most of the valve gear components are straightforeward to make, although the eccentric strap might be worth a comment. The first step was to machine up a bit of bar to 1 1/8 diameter, with a lead that was a few thou less - as a go/ no-go gauge, and also for use as a jig. To machine up the eccentric,(from a casting), I sawed it in two, to form the two halves of the strap, then milled the surfaces square. I used a fine hacksaw blade, and was careful to mill off the least possible metal. Then I silver soldered the cut halves together again, and set up in the 4 jaw to bore the eccentric. (To set up work in a 4 jaw chuck, I use a dial gauge mounted on a tool holder, and TWO chuck keys on opposing jaws. This let me move the work together with the clamped up pair of jaws - much quicker and easier. A simple jig made sure that all four eccentric links were the same length.

The spacing of the coupling rod centres is critical to the free running of the loco. I measure each side separately and comparing it with the drawing. Any inaccuracies in making up the axle-boxes or in setting the crank-pins will show up here. I started by marking out the centres and outline on the rod blank, then drilled the centres, starting with a small centre drill, then drilling out at (say) 2BA clearance at one end, and 2BA tapping at the other. The rods tapered from 3/8 to 1/4 in. - i.e a taper of 1/16 in. on each side. So I marked out the centre line on the support bar, and another, offset by 1/16 in. I drilled and tapped a fixing for one end of the bar on the centre line, and attached the rod blank. Then I lined up the other centre on the 1/16 in offset line, clamped and drilled through 2BA tapping. Now I removed the rod blank, and opened the 2BA tapping hole on the rod blank to 2BA clearance. Also I tapped 2BA threads in the support bar and bolted the two together. I clampe

Just by way of a change, some pics of my finished locos - not me driving! This is a 5 in gauge B1. And this is my A3 Pacific, again in 5 in gauge.

I then turned, bored and reamed the valve chest (sorry, no pics of this) and cut the two recessed passages where the ports were to go, using a parting of tool. Then the ports were drilled and filed all the way through. Accuracy is very important here. The valve chest is to be a light press fit into the cylinder - the end parts of the valve chest stick out of the cylinder, and their o.d. is not critical to the thou. So I turned this part down until it would just pass into its bore in the main casting - then withdrew the tool by a thou (diameter) and cut a bit more. I tried it against the cylinder casting, and checked that it wouldn't enter the bore. I actually went over the surface with some very fine abrasive nylon (like panscrubs) to keep the interference fit to a minimum. The problem is that there is very little metal at the valve area, and it can easily collapse if the press fit is too great. (I've heard it suggested that a sliding fit and loctite might be better - as ret

The cylinders on this loco are gunmetal. Simply because that's what came with the bits I bought! I much prefer gunmetal anyway. I don't run my locos a lot, and worry that cast iron cylinders will rust. The other side of the coin is that you can use conventional piston rings with CI cylinders. The first thing I did was to make up the boring bars. Mine were cross drilled bar, of as big a diameter as could pass through the cast bore - within reason. I have quite a few carbide drills intended for drilling glass fibre printed circuit boards. They do have their uses -but are very fragile. They all have a 3mm shank, which is ideal for making small cutters. They're easily ground using a diamond wheel (but nothing else will do !) The tip is held in the boring bar by one grubscrew which presses on the shank of the cutter, and another grubscrew behind it, which is also used to control the advance of the cutter. I needed to make more than one cutter with different lengths, or a

I started with a set of frames which had already been made. I was going to say - which saved a lot of sawing - but in fact I would probably have cut them in the mill. The important thing is that the two blanks are riveted together and treat as a pair until complete. As I had no idea how mine had been done, I started with dimensional checks. I soon found that the axle box spacing was marginally different (of the order of 20 thou) from one side to the other. And the horn slots had been finished individually and were different (hence the axle box spacing). Apart from that, they seemed ok. I set the frames on parallels standing on a surface table. The structure was not truly parallel, with a rock of at least 1/16 in in one corner. I slackened fixings and kept rechecking, until I found that the central cross braces were the cause of the problem - one was a few thou out of parallel. I milled a few thou off to make it truly parallel, and made up a shim (only 5 thou) to keep the spacing correc