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by Marc Horovitz
|Late in 2011 I got the itch to build another steam engine. I had a lot of irons in the fire at the time, so didn't want to get bogged down by a lengthy design/build project. I wanted to build something relatively quickly. This engine is the result.
On my monorail engine, the steam motor was right out in front, mounted horizontally. On the tram engine, I mounted it vertically in the cab. On this locomotive, I decided to mount it between the frames (unprototypically) and gear it to the front axle. Then I would hide the steam motor with side tanks and make a pair of dummy cylinders to mount outside, in the usual place.
Since the steam motor occupied all the space between the frames, that obviated the use of an alcohol-fired boiler, with wicks underneath. With a single flue, gas-fired boiler, I could put the gas tank in a side tank.
Because the engine is freelance, and because I like British narrow gauge, I patterned it after UK practice. It would have full-length dummy side tanks, a hinged smokebox door, and a big brass dome over the safety valve. The lubricator could sit next to the boiler, behind one of the side tanks.
The reversing valve would be actuated by separate lever in the cab, via a fairly elaborate (but fun) geared system that was done to reduce the lever throw necessary to actuate the valve. I put a big roof over the engine to give the driver protection from the hot Colorado sun.
In due course, the steam motor was finished and running smoothly on compressed air. I then made the frames from 1/16" steel plate, then the wheels and axles. I made my own gears -- something I enjoy doing -- and mounted the little one on the steam motor and the big one on the axle.
Once the chassis was working smoothly and the dummy cylinders and rods were in place, it was boiler time. This I made from a piece of copper plumbing. It has just three bushings: one for the safety valve, one for the pressure gauge, and one for the throttle turret. Assembly was straightforward and I silver soldered all the pieces together, then pressure tested it at 100 psi. All was good.
With the boiler finished, I moved on to the smokebox front, which involved a hinged door that opens for lighting the fire. This was an interesting mini-project in itself. The hinge straps are riveted to the door and the handle actually works as a latch, similar to a proper dart (but there is just one handle).
With the boiler done, I mounted it to the chassis. It was starting to look like a locomotive. I made the boiler fittings, including the throttle valve, the safety valve, and the lubricator. I set the safety to blow at 40 psi. Gaskets for the various bits were cut from a sheet of automotive gasket material that I acquired along the way.
Next came the dome, which began life as a 1-1/4" round brass bar. I cut the hemispherical top end on the lathe with my ball-cutting tool, then recessed the bottom end, leaving a fairly thin wall. I scooped out the bottom to fit the boiler contour, holding the dome in my milling vise and using a fly cutter to do the profiling. I then heated the dome to red heat to anneal it. With the aid of a hammer and a piece of 1" dowel, I beat out the flare at the bottom. When I got it to fit properly, I polished the dome to a high gloss with a buffing wheel.
I had some difficulty with the burner. I built one based on a published design but it was unsuccessful. With the help of a British friend, John Turner, I built a second one, which performed very well indeed. I used an Accucraft jet, turned down and soldered into a small housing to reduce its overall size.
The gas tank is made out of a section of large, square brass tubing that I had on hand. I made the control valve and used a filler valve from one of Harbor Freight's cheap micro-torches.
The engine was now together and could be bench tested. This was done in the usual way, on blocks, and all seemed well. I should mention that I did a very brief test without steam oil in the lubricator. More about this later.
Then it was time for the sheet-metal work. I'm a big proponent of the use of tinplate (tin-can metal) so decided to use it for all of the sheet work. At around .008", it's thinner than than the brass I'd ordinarily use, which is around .020" thick. I was a little concerned that the tinplate would be too flimsy but, as this was a small engine, it might be OK. In the end, it worked just fine.
I had a bunch of empty alcohol cans rescued from one of the Diamondhead steamups, so it seemed fitting to use those on this enging (even though it's gas fired). I cut all of the parts with scissors and folded them up using methods found on the Tinplate Girl web site. I drilled a lot of holes for dummy rivets, which took the form of brass escutcheon pins soldered in place. The tank tops, also tinplate, are screwed on. The rest is soldered. Tinplate's a wonderful material to work with and solders like a dream.
At long last, the engine was finished, with the exception of the dreaded paint job, a task that is guaranteed to put me into a cold sweat at the very thought of it. However, I tackled it. Despite some initial sebacks that involved stripping some parts and starting all over, the job was eventually finished. If you don't get too close, it looks acceptable. The red lining was done with a ruling pen (bow pen) using Humbrol paint thinned with lighter fluid.
I decided to have another go at etching name plates. I had done a little acid etching before with mixed results. I'd heard about galvanic (or electrolytic) etching, so decided to give that a try. I'm not going to go into the details here -- check out this web site to learn more about the process. I found that this method worked well, is safer than acid etching, and less messy.
I stripped the engine down yet again, cleaned out the lubricator, steam lines, and cylinders (messy job!), then reassembled it. I filled the lubricator with some much lighter oil and lit it up again. Yep, that was the problem. This time it ran beautifully.
It runs well on the track, too. Being a small engine, steam comes up quickly. It will run for around 15-20 minutes, which I think is good, given its size and the fact that water cannot be added during the run. The gas consistently outlasts the water, so I have to keep an eye on it when I think it's getting low. It's surprisingly strong, too. It had no trouble pulling three heavy coaches, about the limit of a prototype engine of its size.
You can see it running in the video below. (It's throttled back when pulling the coaches.) If, for some reason, the video doesn't work, click here
|The running chassis. The steam motor resides between the frames and is geared to the leading axle with a 2:1 reduction. The outside cylinders are dummies. The rotary reversing valve is at the rear (left) end.|
|A closeup shot of one of the dummy cylinders.|
|All of the boiler pieces, ready to be assembled and silver soldered. The barrel and the flue are standard copper plumbing pipes.|
|The smokebox door is hinged and can be opened for fire lighting. The handle on the front locks it closed. The hinge straps are riveted to the door.|
|The boiler mounted to the chassis. Frame and footplate are made of steel. The smokebox front secures the boiler to the chassis at the front.|
|Left: At the rear, the boiler is held in place by two brackets screwed to the footplate. The reversing valve can be seen just below the boiler flue.
Upper right: The burner, shown here upside down. When installed, the flame will burn on the bottom.
Right: The dead-leg displacement lubricator, installed on the footplate and plumbed into the steam line.
|Above. The dome, from the bottom, after shaping, profiling to the boiler, annealing, and flanging. Right: The finished dome in place.|
|The reversing gear. The lever is geared to the reversing valve so that when the lever is moved in one direction, the valve is moved in the opposite. This arrangement was actually arrived at because it economized on the space necessary to operate it.|
|The gas tank (left) and backhead, with everything in place. The reversing gear has also been installed on the footplate. The engine is functional at this point in its construction.|
|Tinplate side tanks being tried on for size. Holes are for dummy rivets (escutcheon pins).|
|Access to the filler valve is through a hatch in the top of the side tank. The control-valve handle was made by soldering seven small pieces of brass tubing together, then slicing off a "cookie."|
|One of the link-and-pin couplers. These are milled from a piece of rod, which makes them solid and substantial. They are screwed to the end beams.|
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