The Essential Beginners Guide to Live Steam Models:
Building Model Steam Engines (3)
Whichever is your passion, be it Steam Locomotives, Traction Engines, Stationary or Marine Steam Engines, building them & making them work can either be a pleasurable experience or a nightmare !
Every part of a model engine must be a model in itself, it is commonly found that a model steam engine often looks quite good, but on closer inspection they can be far from good. I come across some horrendous examples of "model" steam engines. It is always down to the builder, Stuart Turner sets of castings make into very good steam engines with the required standard of workmanship, but some that I have seen are only suitable for the scrap bin - !
Here are a few pointers to help the beginner:
Don't be too ambitious, a "Duchess" or "Gresley A4" locomotive is definitely not a recommended option for a beginner. Let's face it - to construct a simple 0-4-0 working steam locomotive is not that easy unless you have built a few, Ebay is full of "part finished" steam models, most are not so good & are typical of builders being too ambitious without having attained the skill level required to complete such a model.
I would highly recommend starting with a simple stationary engine such as a Stuart Turner Victoria. This model is not too small & fiddly to make, and it is very simple to machine, and if you foul up, extra castings are available from Stuart Turner anyway. If you complete this model & it runs well, at least you have a substantial model steam engine to either play with & show off to your friends or sell for a good price. I find that smaller steam engines are a bit fiddly to make, whereas the "Victoria" is quite easy to build and the parts are not microscopic.
When building a steam engine the best way is to sectionalise the build in your head first - think the build through before you start.
The Connecting Rod(s)
Before you start, study the drawing carefully & make sure that you know why you have to make this part as accurate as possible to the drawing.
A steam engine connecting rod is usually one of the simpler parts to make, but a few notes her will not go amiss.
The main points to watch are:
1) the connecting rod needs to be the right length.
2) the big end & little end holes must be in line with each other.
Making a connecting rod from a solid bar is a plain lathe turning job initially, the only difficulties encountered will be if the rod is thicker in the middle that at the ends.
All you have to do is cut at a slight angle at each end towards the middle, then use a file to make it not look machined & remove the tool marks Finish off with various grades of emery paper followed by "Scotchbrite" (the green scouring pads).
Think about it - in the full size, a connecting rod on a mill type engine is very long indeed. The reason for the rod being thicker in the middle that at the ends, is not for decoration, but to impart uniform strength along the rod & to resist flexing. If the rod was parallel all the way along its length, it would be likely to bend in the middle. Although it is unlikely to bend in a model, the time & effort required to make a rod to "scale" dimensions is well worth the trouble.
Once the rod is turned to dimensions, the next & most important part, is to mill & then drill the big & little ends flat to fit the crosshead & crankshaft.
Once you have a rod that has the required flat parts at each end, mark out the length accurately then drill the bush mounting holes. This can be done in a 4 jaw chuck in the lathe if you have the centre height clearance to swing the rod, or on the pillar drill. Either way it is vital that both the holes are absolutely 100% in line with each other. If they are not, then the finished engine will bind. The engine will also "knock" or "click" when running, as the connecting rod constantly tries to re-centre itself.
Always recheck your work & do not proceed with the rest of the engine until the connecting rod(s) are 100% correct. If you carry on now, with the connecting rods(s) not right, you will end up in trouble as usual - later on in the build.