The heart of the beast

If you can imagine the human body, you can get an idea of how a steam locomotive would work. These small scale models are working models of the prototype, or "life-size" steam locomotive. This Aster USRA light Mikado is 1:32 scale or "Standard gauge". What this means is that it would take 32 of these small scale engines to represent the length of 1 prototypical sized USRA light mikado. It would take 32 stacked atop each other to represent the prototypical height and the same for the width. So all total, it would take 32,738 of these small scale live steamers aranged in 32 high, 32 wide and 32 long to equal the general outline of the prototype USRA light Mikado. (Thanks Charles)

As to our comparison here, in the human body you have the brain which sends the signals to the heart to beat which in turn sends out the blood to the parts of the body enabling it to do what the brain tells it to do. In much the same way, the engineer is the brain of the train and he would turn valves and pull levers which would send signals to the brakes, cylinders, pumps and valves to work the engine. The blood is replaced by steam in the train which enters the cylinders (heart) and moves the cylinder piston to generate motion to the coupling rods which move the driver wheels all together.

This is quite a simple comparison, but I am about to put together the heart of this beast I am building. The first thing I need to do is "lap" the face of the cylinder block and the bottom of the slide valve which will slide over the ports, which in turn allow the admission of steam into the cylinder and the outlet of exhaust into the smoke stack. When Aster machines the cylinder blocks and slide valves, little marks where the parts were milled can be seen. Putting a piece of emery paper on a flat and thick sheet of glass or a mirror allows me to smooth out these traces and gives the surface a very smooth and mirror-like finish. The Thick glass assures a flat and level surface.

I was advised to do the lapping in a "figure 8" motion so as not to apply uneven pressure going in a back and fourth motion. Some will lap with various grades of emery cloth from rough to fine and get that surface to a literal mirror-like finish. Others will do just enough. I was told by a man who works on these that no matter what finish, in the end, the slide valve will eventually create normal wear and one day for an overhaul of maintenance I might have to lap them a bit more.

I obviously will lap them enough where I won't have any steam leaks as the gasket material will create a seal between the cylinder face and valve chest. The few groves that may be left would also allow good adhesion for the cylinder steam oil. Here is a great point to say that there are differences between oil and steam oil. The basic difference is that steam oil has tallow in it which allow the oil to bond with the steam and still allow lubrication in the Cylinder assembly. For further reading on the differences you can check this article which is posted on Jim Pitt's site. http://www.southernsteamtrains.com/misc/steam-oil-hwade.htm

I have decided at this point to lay out all the pieces required for the next section on a white towel. This will serve two purposes. Firstly, it will be a great way to show the many small pieces which make up the final build and secondly it will affirm that all pieces are accounted for and milled correctly.