Drawings - Errors, Modifications and Additions

Fortunately, the drawings have very few errors, this is certainly a help for a first time builder like me! I'll attempt to document the errors I found as I complete this page of the website. I'll cover a few things in general, then things specifically, item by item on a page under this main page.

Screw Threads

One of the first things I changed, were the B.A. threads to U.S. machine screw threads. B.A. stands for British Association thread. These threads are still quite popular with model makers in England. If I had lots of these taps and dies, I would probably have left them as is. But, I live in the Unites States and my shop is filled with machine screw fasteners, taps and dies for small threads. So, all B.A. threads were changed to U.S. machine screw threads. I picked U.S. sizes that were very similar to the the B.A. diameters and there have been no problems.
I did not change most of the M.E. threads. These are a series of threads in fractional inch sizes from about 1/8" to 1/2". M.E. stands for Model Engineer. They are either 32 or 40 threads per inch. Most of the bushings on the boiler are M.E. threads and I did not want to change these. Most of these taps are available new, in high speed steel from Ebay. I have also used these threads on many of the compression fittings for the piping.

Cylinder Bore

As was suggested by several folks in England, and also through calculated results from a model locomotive boiler spreadsheet, the cylinders are a bit large for the Super Simplex boiler and size of grate. So, I have reduced the cylinder bore from 1-9/16" to 1-3/8". I looked at many 1" scale locomotives and concluded that with a bore of 1-3/8", there would still be plenty of power.
What happens if the bores are too large? Well, the boiler will not be able to keep up with the steam demand of the cylinders. They will use steam faster than the boiler can provide it. As for power, with a full head of steam, you cannot stop the wheels from turning, power is simply not a problem. The problem with small locomotives, is keeping the wheels from spinning, not power. I was pleasantly surprised, there is plenty of power with this little locomotive.


On the boiler, I made several changes. These changes were suggested to me by an experienced model engineer and boiler maker in England. The first was to add clean out plugs at the base of the back head. Also, to add several more stays on the left and right water legs of the fire box. I also added a few to the back head. I also added threaded blind bushings to the sides for the expansion brackets and blind bushings to the back head for attachment of the fire box door hinges and latch. The older method was to drill and tap the boiler directly for  these. Today, it is not done that way and anything attached to the boiler should be fastened into a blind threaded bushing.
The crown sheet girder stays I left as per the drawing. But, in Australia this would not pass inspection. In Australia, the crown sheet must always be attached to the outer wrapper of the fire box. Attaching the crown sheet girders to the outer wrapper is an extra challenge for a first time build, and since many of these boilers have been successfully constructed as per the drawings, I built my fire box crown sheet and girders exactly to the drawing. I also checked with the boiler inspector at my club track, to okay this.  

Smoke Box Draughting

Another suggestion give to me by an experienced builder, was to make a slight change in the smoke box to improve draughting. The modification was to bring the bottom of the smoke stack a little closer to the exhaust blast pipe.


The piping for this locomotive was omitted completely from the drawings. It was assumed that the builder knew how to pipe up a miniature locomotive, of course, this is not true, especially for a first time builder. I have a schematic drawn, and posted for down load, that shows how I piped my locomotive, it is on the Plate Work and Piping page, under Water Tanks and Plate Work . One thing I did that is not typical, is I piped the discharge from the hand pump to go into the axle pump. This allows the hand to be used to "prime" the axle pump. This was suggested to me by a friend at my club and so far, seems to work well. It does cause you to install an extra check valve in the supply pipe to the axle pump, so the hand pump does not simply put water back into the tank. When piped this way, you can open the by pass valve and witness water coming from the discharge of the axle pump. Close the valve, and now the hand pump is putting water into the boiler.
My piping schematic relies on a water supply from a tender car that is piped into the water tanks on the locomotive. There are two supplies from the tender, one that feeds the tanks, and a dedicated supply for the injector. This way, the injector always has a cool supply of water, which is important for an injector to work well.

Cab & Water Tanks

The outer side of the water tanks and the cab, as drawn, are to be made from a single piece of material. This makes for a very difficult assembly, and causes trouble shooting without the cab impossible. Since this is a freelance miniature, it can, of course, be built however you see fit. What I have done, and several others I have seen on the internet, is to make the cab separate from the side water tanks. In my case, the cab can be removed by unscrewing only 8 screws, leaving the tanks in place. Also, I have left enough room under the water tanks to allow for all of the pipe fittings to be placed underneath the tanks and avoid having any of the piping go through the running boards. Also, the balance pipe between the tanks goes under the boiler instead of through the cab as suggested. Also, I have used 1/16" brass plate for all of the plate work on the cab and water tanks. In general, there also seems to not really be enough construction detail for the cab and tanks, so, the builder is somewhat left on his own.

Cylinder Drain Valves

It almost seems that the cylinder drain valves were an after thought. As drawn, there was no way I was going to create a system of levers and rods to operate the drain valves. I designed a completely different system of levers and bell cranks to do the same job. There are photos of what I have done in the Build section.

Running Boards

I have divided the running boards into three pieces, the drawing shows them as one piece. One joint is directly in front of each water tank right at the motion plate and the other is somewhat under the side water tank, right at the support bracket.


The drawings show brake shoes on all six wheels. I have not done the brakes yet, but, it looks like there is not much room for shoes on the forward wheels. Some builders have simply put brakes on only the center and aft wheels.