Build a See-Through Model Steam Engine

Modeler's Corner


| September/October 2004



Tips for building Lucy

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.