The Essential Beginners Guide to Live Steam Models:
Building Model Steam Engines (1)
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 most important parts of a steam engine are the Crankshaft & Main Bearings - if these are not right in the first place - the engine will not work very well at all.
Steam engines work on a push pull cycle on the crankpin, so if there is "slop" or "binding" anywhere, this sequence will be affected. "Slop" will cause "knocking" binding will cause erratic running.
The Flywheel
Machining a flywheel is straightforward, but if it is a large cast iron flywheel, don't rush it - always run the lathe at a low speed - this is the best way to cut cast iron on a modeller's lathe to avoid "chatter". Using a carbide tipped lathe tool is a good option also, not essential though, as a normal high speed steel tool is also adequate. Follow the instructions in your "book of words" for the machining sequence. Always clean up the casting with a file prior to machining. One school of thought is to fully clean up the spokes & fully paint the flywheel first, then machine it. This is a good idea, but I would usually only spray primer the flywheel casting before machining it. I prefer to paint the spokes by hand with a good quality enamel paint.
The Crankshaft
A good crankshaft is not an easy component to make either. It must run 100% true otherwise the flywheel will wobble which looks awful on a model. When machining the crank, it is vital that the crankpin is truly 90 degrees square to the crank web & crankshaft. If it is not, the engine will "knock" when it is running as the connecting rod will run out of true on every stroke. Take your time with this item & get it right first time. Turning a crankshaft from the solid is not recommended for beginners, use the "built up" method preferably silver soldered, although good results can be achieved with "Loctite", it is vital to drill the crank webs & fit pins to secure these components, as in operation even a model crankshaft is under enormous mechanical loading. Once the crankshaft is finished, spin it up in the lathe to check for true running. If it is slightly out, while still in the lathe chuck use a dial test indicator & a little "persuasion" to straighten the crankshaft.
The Main Bearings
It is assumed that a beginner will have bought one of the books available to help with workshop practice. There is a definite sequence of events required in order to successfully make split main bearings which are then adjustable for wear. The purpose of this article is not to be a step by step instruction set, but just a general guide.
So now you should have a crankshaft, flywheel & a nice set of main bearings.
Bolt the main bearings to your bedplate casting(s) as per the drawing & fit the crankshaft using a little oil on the components. The crankshaft should not be a "rattle fit" nor should it be tight. One method is to initially make the bearings slightly undersize, fit them to the bedplate, then run a hand reamer through the lot. This will ensure accurate alignment of the main bearings. Oil the bearings and rotate the crankshaft with your fingers. If there are any tight spots, check your dimensions & refit. You may have to "shim" the main bearings where they contact the bedplate if there are any major inaccuracies. Once the crankshaft spins freely, test fit the flywheel to the crankshaft & make sure that it also runs true. If it does, then great - if it doesn't - something is wrong. Recheck your work & do not proceed with the rest of the engine until the crankshaft is 100% correct. If you carry on now, with the crankshaft not right you will end up in big trouble later on. You have been warned - !