CONWAY: NOVICE GUIDE TO LOCO BUILDING

LOCO BUILDING Conway – a first steam locomotive build

Rich continues his short series designed to help novice builders facing the challenges constructing a fi rst engine – this month, don’t believe all you see in plans...

BY RICH WIGHTMAN Part two of a short series

Okay, having read the first part of this series last month you have decided on which loco to build. You have your machines and hand tools. You have your set of plans and some materials to hand and you are keen to make a start. Firstly, if possible get the plans scanned and saved as a PDF file.

I have used my home A4 scanner to copy small sections of plans. Using one of the many drawing programmes out there (you can find many free ones online – I use a programme called Inkscape which is open source and is free to download) you can clip just the bit you want and print it out to a very accurate actual size.

I found doing this to be of great use – you can visualise quite clearly the size of the part you are making and lay said part on the print of the drawing as many times as you want. You can make your own notes on the drawing print and if it gets too dirty simply print another. It means you can keep the original set of plans clean and only use them when needed.

If you are buying a new set of plans from one of the suppliers ask that they are rolled and not folded. The crease marks can be annoying and make some of the smaller details and measurements hard to read. I have seen plans for sale, and sold on Ebay for a higher price than a new set, I wonder why?

Study the plans well and inwardly digest. If there is something you don’t understand ask a question on one of the model engineers’ forums we discussed in part 1. Someone will answer and explain in detail the problem you are having.

Another word of warning here – there are routinely errors to be found on plans. There may be just one or two but some designs are apparently littered with mistakes. This is where a good search on the internet is very useful to see if anyone else has had problems.

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“Had I not read the drawing correction in the magazine a very expensive mistake would have been made by cutting the boiler tube too short...” Not adding up

If the design was published as a series of articles in one of the model engineering magazines they may have published the errors but not always. And the errors can be significant – as an example on Conway the boiler length on the plans is 14 inches but in actual fact it needs to be 14¼ inches. The error was published in the magazine the loco was described in but had I not read that a very expensive mistake would have been made by cutting the boiler tube too short! Even though the error was published the original plans were never altered and still contain the incorrect measurement. So it’s very important that you study the plans and make that sure all the numbers add up!

A few more examples of errors I came across on my build, starting with the valve rod guides. Take a close look at the drawings of the valve rod guides and the stretcher onto which they fit or should I say are supposed to fit, Photo 8 and Photo 9. There are six holes in the valve rod guides and four holes in the stretcher!

I had made the guides and

stretcher at different times so didn’t notice the error – Hmmm? After a bit of head scratching I decided it was easier to remake the guides than remake the stretcher that was already fitted in the frames.

Another example concerns the blast nozzle and jets. This is quite a complicated little part that requires precise machining (Photo 10). I followed the plans religiously, making each part to the dimensions given only to realise too late that the dimension of 11/16-inch (indicated by the red arrow) on the plans is wrong and should be 13/16-inch – another piece of bronze launched unceremoniously into the bin.

There is also an error in the dimensions of the horn blocks and a correction to this was published in a later edition of the magazine, stating that their overall height should be 113/16-inch and not 25/16-inch! Yet, if you buy a brand-new set of plans for Conway today they will still contain the errors I have mentioned! I understand it’s something to do with copyright why they have never been amended. The moral of this little tale is that you must take a look at each part, look at where it fits and check that all the numbers do add up.

Measure for measure

What shall we talk about next? I know lets debate the imperial versus metric argument. If you are old-school then imperial measurements won’t bother you and you will have taken metrication in your stride. If you are of a younger generation and brought up in the world of metrication then converting back to imperial may be a challenge, but it’s one I think you will have to master.

Most if not all of the plans available today were drawn many years ago and have imperial dimensions. Converting all the measurements to metric is not impossible but might not work in certain circumstances.

Some materials might only be available in imperial and vice versa – for example the frames on Conway are 1/8-inch steel. I managed to source some 1/8-inch material but the most common size these days is 3mm. Near enough you might think but 1/8-inch is 3.2mm. If you make the frames from 3mm and make all the stretchers to plan then the distance between the inside of the frames will be correct but the outside measurement will be 0.4mm (0.016-inch) narrower than the plan. It doesn’t sound much but it could mean alterations to axleboxes, axles and such will be necessary.

Most of the fittings you will need such as safety valves, water-level gauges, blowdown valves, cylinder draincocks, blower valves, whistle valves and clacks to name just a few examples have imperial threads, with 26, 32 and 40 threads per inch being the most common.

While it is not impossible to make all your own fittings and use metric threads – the plans will have details of the fittings – you must remember to make all the bushes and such with a matching thread. I have made some, water gauges and clacks, but find the tiny parts too small for my fumbling digits and the commercial ones are reasonably priced.

Those of us using older machines – my lathe is a Myford ML7 – are probably working in imperial anyway. My milling machine, however, is one of the Chinese variety and is in metric. Digital readouts are the answer and can be fitted quite easily. I have the example in Photo 11 fitted to my machines, supplied by Arc Eurotrade (usual disclaimer) and which come with its own display. I have each coupled to the free download called TouchDRO (Photo 12) which works on any android phone or tablet.

Many people simply modify the cheapo 6-inch digital calipers which work perfectly well and switch between imperial and metric. I have one fitted to the tailstock of the

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PHOTO 8: Original drawing of the frame stretcher – note the four holes specified for each valve guide...

PHOTO 9: ...whereas on the drawing of the guides themselves, six holes are specified!

PHOTO 10: More potentially expensive errors – the highlighted measurement of 11/16-inch should be 13/16...

PHOTO 11: This unit from Arc Eurotrade is typical of the digital readouts that are available.

PHOTO 12: TouchDRO – a free download for use with Android phones or tablets.

All photos by the author

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Myford with no problems at all (Photo 13).

To sum up, I think you will have to become conversant in both imperial and metric measurements. The plans will specify a few different sizes apart from imperial such as number and letter drills and BA size threads. I have charts printed out and pinned to my workshop walls for easy reference.

Another decision to make early on is to what degree of accuracy you want your model to be. Do you want a show-standard, accurate down to the last rivet, work of art or do you want a loco that is a reliable runner that you can take down to the track with minimal effort and maintenance. I chose the latter.

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PHOTO 13: For ultimate lack of cost a digital caliper can be adapted to ser ve as a machine tool readout...

PHOTO 14: Button-head screws make believable rivets. Changes can be made

On Conway I have made a few alterations to the original design, the main one being to fit side tanks rather than the original design’s saddle tank – I did it for no other reason than I prefer the look of side tanks.

My tanks are quick-release units being held on with two M6 bolts. The cab is also quick-release and is held onto the loco with eight thumb screws. I have also made split axleboxes which incorporate underslung coil springs instead of the leaf springs in the original design.

Where possible I have used stainless steel in my build – the valve rods and brake gear for example are all in stainless steel. They are inside the frames so can’t be seen anyway. The running boards are stainless steel, as yet unpainted and may remain so – they are dead easy to clean requiring little more than a wipe with a rag.

The Conway plans mostly specify the use of BA-size nuts and bolts. BA nuts and bolts have a head size smaller than normal which look more to scale. I have used stainless-steel nuts and bolts in mostly metric sizes, some socket-head cap screws, some with stainless-steel nyloc nuts. They are relatively cheap to buy compared to BA and readily available.

To do this some holes may have to be drilled slightly larger. For example 4BA = 3.6mm so the holes will have to be drilled to accommodate a 4mm bolt. 7BA = 2.5mm so can easily be substituted by 2.5mm bolts.

Also available in stainless steel are button-head screws which I have used around the smokebox to good effect, they look a little like rivets (Photo 14). Whilst I admire the level of skill to which some builders have reached I’m afraid I have not yet mastered the art of riveting nor do I to some degree have the patience. I have tried my hand at riveting and just could not get it right so I’ll stick with the buttonhead screws for now.

Okay, just before we start on the build, what to do about the boiler. If you are building a model purely for show then this is not an issue but if you intend to run it then make a decision early on. This is I believe why we see many unfinished locos for sale, some with all the boiler materials included. Builders get to the stage of needing a boiler and then back out. I will quote Martin Evans from the Conway magazine article; “It seems that quite a few locomotive builders find boilermaking more difficult than machine or chassis work. This is rather difficult to understand, because in many ways, boiler work is easier than chassis work and, furthermore, it does not take nearly so long provided the essential equipment is available.

“Whereas in chassis work, we have to work frequently to ‘thous’ (sometimes even to half-thous!), on boilers, we shall not do too bad if we are within 1/32-inch on the longitudinal dimensions, or 1/64-inch on our widths”.

It is a little daunting, the idea of making a boiler and I must admit I had been putting it off for quite a while. But the time had come to get on with it. I couldn’t justify the expense of buying a commercially-made boiler, some run into thousands of pounds with a two-year waiting list, so the only option was to do it myself.

Firstly, before any materials are purchased, speak to the boiler inspector at your club. He will advise you on what to buy and he will want to see it at various stages of the build.

Boilermaking gear

What is the essential equipment? Well you need a hearth of adequate size for a start. Mine is a cheapo Workmatetype bench fixed solidly to a plywood board and mounted on heavy-duty braked castors (Photo 15). I can move it from the corner of the workshop to nearer the door for better ventilation when soldering.

It is topped with a sheet of 6mm thick steel that I won from somewhere. I use Vermiculite firebricks on the base and surrounds which can be stacked to suit the job in hand.

A propane gas bottle and torch is next on the list. Propane burns hotter than butane, and you will need lots of heat. I initially started with a cheapo torch kit from one of the major tooling outlets which was okay for a start but as the boiler progressed and became larger I was struggling to get enough heat into it.

At the time I had access to oxy-acetylene gear which was a great help. The fine f lame was great for