The Essential Beginners Guide to Live Steam Models:
Building Model Steam Engines (2)
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:
Dont 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 Cylinder(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.
There is a slightly different technique for machining gunmetal & cast iron cylinders. Mainly, as gunmetal is a very soft material, you may have to use brass packings on the chuck jaws to prevent marking the work. Cast Iron is very hard & is usually OK mounted directly in the chuck, but it is a good idea to use packings when machining the port face so as not to mark the ends of the cylinder.
The way I usually do it is to initially clean up the cylinder casting with a file, then mount the cylinder casting in the 4 jaw chuck with the core hole running as true as possible, take a cut or two across the face, the last one being the finishing cut, then bore the cylinder all in one go. Boring the cylinder is easy enough, just take your time - especially with cast iron & use a nice sharp boring tool. The first cut needs to take a good "bite" to get through the skin of the casting. Bore to within a few thou of the finished size, then bore almost to the finished size & reverse the longitudinal traverse on the lathe so that the tool comes back out of the work, and repeat this process a couple of times. You should have a cylinder with a really good smooth finish if you do it like this. If you are not happy with the finish, use a cylinder hone on the bore when the other end of the cylinder is machined. These cheap cylinder hone sets are readily available from Ebay & are very useful to have in your workshop. I am assuming that your lathe cuts parallel - if you end up with a slight taper, the hone will help also, but it is not the answer! It is a good idea to do a test on a bit of scrap to verify that your lathe cuts true, before machining your expensive cylinder casting. You should now have a true cylinder with a parallel bore, dimensionally accurate to the drawing.
Next, machine the valve port surface in the 4 jaw chuck, then once this is done, drill the steam ways if the ports are cored in. If the ports are not cored in the casting, you will need to mark them out on the port face & use a slot drill in a milling machine (if you have one) to machine the ports, or mount on a cross slide with a slot drill in the chuck to carry out the maching process. Either way - really think about this part of the process, as it is dead easy to foul up & spoil the work at this stage. For drilling the steam ways, either file or mill a flat in the inside edge of the cylinder (on the steam port side!), then centre pop the hole locations & with the cylinder mounted at the correct angle in your milling vice, carefully drill the ports at the correct angle so the drill doesn't burst through the port face - ! Clear the swarf regularly, as a drill breaking at this stage would not be a good thing either.
Once the ports are milled & the steam ways drilled, all that is required now is to drill & tap the holes for the cylinder covers. This needs to be done after you have machined the covers & drilled the holes in them for the cylinder cover bolts. Use these covers as a drilling jig to ensure correct alignment of the holes. Again, clear the swarf regularly & don't rush the tapping - especially whilst in the middle of tapping a thread in one of the holes. Also - don't drop the casting on the floor as I once did - breaking the tap - !
Recheck your work & do not proceed with the rest of the engine until the cylinder(s) are 100% correct. If you carry on now, with the cylinder(s) not right, you will end up in trouble as usual later on in the build.