Build a See-Through Model Steam Engine

By Staff
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Hello again everyone. Recently, I  had the pleasure of talking with model engine designer and builder Ed Warren, whose model plans once appeared regularly in the now-defunct ModelTecmagazine. The subject of our conversation was, of course, model engines, and we discussed a model Ed designed some years ago as a teaching aide to show people how a simple steam engine works.

The ‘Lucy’ model is made out of see-through, 1/2-inch Plexiglas (or Lucite, hence the name ‘Lucy’), and the thought of a see-through model engine really sparked my interest. Although it’s a steam engine, this is a great project for anyone interested in model engines – especially first-timers.

Lucy is a ‘wobbler,’ or oscillating engine. The cylinder is attached to the base by a single bolt and pivots on the base as the crank spins. The intake and exhaust ports are drilled into the base, and a single port is drilled into the side of the cylinder. As the cylinder pivots against the base, the ports are exposed or closed.

Ed says to drill the Plexiglas at high speed and to use kerosene as a lubricant. The drilling went perfectly, with only very small drill bit markings in the plastic. Ed tells me he has never used a drill jig, and all I did was tape the plastic for my hole markings and then used my drill vise to hold the parts.

I made a few changes, which included fitting a 1/2-inch-larger flywheel I already had on hand (the larger the flywheel, the slower the model will run). 1 also made my own hose coupling for the intake port on the front of the base. Ed’s plans call for a 14-28 tap and two 14-inch pipes or tubing for the intake and exhaust tracts. I remembered a friend talking me into using tire valve stems for my propane demand regulators, and I incorporated that approach here.

To do this, I removed the core from the stem and threaded the stem into a jig 1 had built and then burned the rubber off with my propane torch. After it’s cooled, I chuck the stem into another fixture in my drill press and polish it. It sounds like lots of work, but in fact it’s easy and only takes a short time to do. A valve stem takes a 5/16-32 tap, and most tool stores will have this tap in stock.

All told, I spent more time finishing the flywheel than 1 did building the model. It runs very well with very little air – just 2 psi – and it’s a treat to watch in action.

The Next Model
The next model I’m going to build will be the 14-scale Gade from Morrison & Martin in Benton City, Wash.

It’s a very clean kit, and I ordered it with the gear set and all the small parts and accessories (along with the oiler) that are available. The plans look very concise, and once the show season slows down a little it will be off to the shop to start making some chips! I also got one of the tiny 10-40 spark plugs and am excited to see such a small plug work. Is this hobby great, or what?

This month’s tip for model and scale parts source:

Morrison & Martin has casting kits for the 1/4-scale Gade I will be building. (509) 588-3829;

Ed Warren has books on building wobbler steam engines. 11996 Gast Road, Bridgman, MI 49106; (269) 426-3596.

These tips are for your thoughts only, and your fuel lines may vary.

Tips for Building Lucy
By Ed Warren

Years ago, I discovered that teaching about steam engines would be much easier with a see-through engine. Since Plexiglas is readily available at most hardware stores, I chose it as my medium. The following tips are for building a plastic steam engine. I might add that even though it’s made of plastic, it will run on air quite well.

Using a high-speed setting on your drill, and using kerosene as a lubricant, slowly drill with light pressure. If you apply too much pressure, you will break out the comer of the plastic. High speed in the milling machine has the same effect; it seems to polish the edges as it cuts.

If you can’t find Plexiglas, then brass, steel or aluminum can be substituted. On this particular wobbler, the flywheel was made as big as possible to slow down the action so the power and exhaust strokes could be seen in operation.

Starting with the base, carefully lay it out and drill the holes. I have never used a drill jig for drilling, and maybe some day I will give that a try. This plastic is quite strong and holds threads well.

No bearing stock is used on the cylinder plate because it tends to hide some of the simplicity of the engine. Aluminum is used for mounting the engine, which also gives something to hold on to while showing it (the plate has holes in the corners to mount it to a table).

Carefully drill the cylinder after cutting and milling. The piston can be made out of brass or stainless steel and buffed to a shine so it can be seen through the plastic. Buffed brass looks good for the flywheel.

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