Miniature steam engines run in the family.

ost steam engines have disappeared from use or been put in museums, but after 60 years in the business Thomas Jensen continues to build and sell working miniature models, some of which weigh as little as 2 lbs. Sales of the tiny machines have supported him and his family since the 1930s. Now,

Jensen, a Danish-born mechanical engineer, admits that he is most content in his machine shop, a small garage-like building almost invisible to passersby. Inside, between 3000 and 5000 tiny machines, about % the size of full-scale steam engines, are churned out each year.

His company, Jensen Manufacturing Company Inc. (Jeannette, Pa.), is very much an extension of its founder. Jensen's son, Tom Jr., is president of Jensen Manufacturing. He too is a mechanical engineer, as is Tom Jr's son, John, who works for the Norfolk Naval Shipyard (Portsmouth, Va.) and plans to one day take over Jensen Manufacturing and carry on the tradition of steam engine making in the U.S. well into the next century. (John has been a member of ASME since 1990. His interests are in design engineering, and fluid power systems and technology.)

The low profile the senior member of the Jensen family, Thomas, has kept throughout his life has underplayed his career's achievements. "Everything is carried out totally incognito--that's my dad's style," said Betty Meil, Jensen's daughter, who herself is the mother of two electrical engineers. However, Jensen's achievements haven't always gone unnoticed. President Bush recently wrote a congratulatory letter to Jensen for his 91st birthday. Jensen's efforts have "inspired those around [him] and have set an example for others to follow," the president said.

Humble Ingenuity

Many in the miniature steam engine fraternity are surprised at the ingenuity that underlies some of Thomas Jensen's creations. But to him there is nothing wondrous about much of what he does; whether that be machining within tolerances of [+ or -] .0005-inch or making boilers that last for decades. For one particular part of the manufacturing process, Jensen built a tube-cutter that saws off small brass boilers to length from the inside. "That's very simple, there's nothing special about it," he insisted. But according to miniature steam engine hobbyists, the cutter is rare for the manner in which the tubes are sawn off. In this case, the use of multiple steel cutting wheels spinning around both the inner and outer circumferences of the tube reduce the chances of part deformation.

"What is simple to Mr. Jensen is mind-boggling to most of the rest of us," said John Foskett, director of marketing at Jensen Manufacturing. Almost all of the molds, jigs, and fixtures used to make the steam power plants were crafted by Jensen himself. Many were designed and built without drawings. (Jensen Manufacturing has recently drafted working specifications for most of its equipment.)

The miniature steam engines Jensen fashions with the help of about seven workers are among only a few currently being built worldwide. Two other firms, Mamod Ltd. (Slough, England) and Wilhelm Schroder GmbH & Co. (Ludenscheid, Germany) are the leading producers of these machines. Each manufacturer sells the table-top machines as hobby items and toys.

Many of Jensen's engines, however, are also bought by colleges and utilities, which require that the machines perform actual engineering tasks. For example, Jensen's No. 51 power plant is hooked-up to an ac/dc generator that produces 3.5 volts, turns on a light bulb, and runs a miniature electric motor. Utilities, such as Philadelphia Electric Co. and New York State Electric and Gas Corp. (Ithaca, N.Y.), use the machines in demonstrating the generation of electric power to customers, employees, and school children on field trips. In the miniature power plants, steam displaces a reciprocating piston that turns a crankshaft and flywheel. Mechanical energy is transmitted by a belt from the flywheel to the generator. In a typical modern electric utility, the steam is used to run power turbines.

Thomas Jensen's passion for building steam engines can be traced to his boyhood days on a farm in the outskirts of a town called Marstal, on. an island off the southeast coast of Denmark. Jensen said he obtained many of his inventive inspirations from watching a horse-drawn threshing machine, powered by a steam engine, that rode by his family's fields every summer to harvest wheat.

In 1931, four years after receiving a degree in mechanical engineering from Copenhagen Polytechnic Institute, Jensen came to the United States. Unable to find work, he immediately began to build miniature steam engines in order to make a living.

Besides steam engines, Jensen has built thousands of tools used in the manufacturing process. For example, he invented a radial drill press that bores 10 holes simultaneously in boilers, which years ago were put together using rivets and a tin-lead solder. The machine is driven by an electric motor whose power is transmitted by a serpentine belt running on wooden pulleys. Also, in many of the model steam engines, the boiler sits on a base of simulated firebrick stamped and shaped from metal with a tool fashioned by Jensen.

Hobby and Commercial

Jensen Manufacturing sells separate hobby and commercial versions of the miniature steam engines. Prices range from $99.95 to $5000. The less expensive engines are hobby versions, which are made of materials such as brass, stainless steel, and a polished nickel plating. All but two of these engines burn oil-based dry fuel pellets that, according to Foskett, emit a very clean smoke and leave no residue. These engines weigh up to 6 lbs.

The commercial models are much heavier because they use cast iron parts, including a flywheel and engine platform. Also, in all of the commercial models, steam is generated with the use of immersion heating rods. Jensen's first commercial prototype was built in 1922. The production engine that resulted weighs 170 lbs and operates on 80 psi of steam pressure. These commercial machines are now available in four models. The No. 50 power plant model, for example, was fashioned in the late 1930s. It consists of a 5-inch diameter by 10-inch long nickel-plated boiler, a steam engine, and a generator that produces 4 volts of alternating current. In the 1970s, an electronic control unit, switches, gages, and a 1/2-gallon capacity water tower were added to the No. 50 engine by Randy Calhoun, an electrical engineer at Hilton Davis Co. (Cincinnati). Calhoun, according to Foskett, owns the largest collection of Jensen machines in the world.

The steam engine Calhoun helped modify became the No. 51 power plant, Jensen's flagship model. In operation, the No. 51 uses a feedwater pump with a stainless steel piston that shuttles water from the tower into a boiler. Inside the boiler the immersion heating rods turn water into steam. Through the appropriate inlet port and at the correct time in the engine cycle, the steam is directed by a stainless steel slide valve into a precision-machined double-acting cylinder (with a 7/8-inch diameter bore by 1-inchtong stroke). That causes a displacement of the machine's piston. The slide valve directs the steam into one end of the cylinder and then the other to complete a full piston stroke.

A governor controls the volume of steam entering the cylinder and, thus, the speed of the engine. Under heavy loads, however, a larger quantity of steam has to be funneled through the governor. That is achieved using three 375-watt immersion heating rods in the boiler, which allows for the provision of extra steam as it is needed. When the steam engine is required to supply more power to overcome loads, toggle switches are activated. Either one, two, or three heating elements are used at one time. "This concept helps illustrate how electric utilities generate more power in hours of peak demand," Foskett said.

World Record Attempt

This month, one of Jensen's commercial power plants will attempt to gain a Guinness record as the longest continuously running miniature steam engine in the world. The Guinness Book of World Records holder is a model steam locomotive that has operated for 144 miles in 27 hours and 18 minutes. "We've already beaten that many times with the model we're using," Foskett said.

In the competition, to be held at The Carnegie Science Center in Pittsburgh, the Jensen team will use an 18-year-old prototype that usually employs a coffee can and funnel as a water tower. The coffee can is the main body of the water tower and the funnel is its roof. Since the tower does not hold enough water for use in the competition, it will function merely as a display item and be replaced in use by a container constructed from one of Mrs. Jensen's household cooking pots.

The old steam engine prototype has already turned through about 113 million cycles, running at 100 to 200 rpm during 8000 hours of operation. Previously, it has operated without stopping for 3000 hours over five months. As far as Guinness is concerned, however, that is unofficial. Generally, Jensen steam engines run at up to 1OOO rpm.

Pint-Size Educator

The miniature steam engine extends beyond use as a hobby item or demonstrator of electrical and mechanical power to uses in college classrooms. In the past year, for example, 190 students of mechanical engineering at Carnegie Mellon University (Pittsburgh) have taken a course designed around the use of Jensen's machines.

Applications for enrollment in the class have been beyond expectations, said Bob Sturges, a professor of mechanical engineering at Carnegie Mellon, who teaches the course. Sturges, an ASME member since 1990, has come up with ways of linking Jensen's machines to the less physical aspects of mechanical engineering, such as calculating torques, speeds, and power. In doing this, he hands a Jensen steam engine and an Meccano Erector set to groups of two students and asks them to work out ways of calculating and measuring the power of the engines under different loads.

The engineering students at Carnegie Mellon use the gears, shafts, screws, plates, and other components of the Erector set to link the steam engine with a generator, a volt meter, and a spring dynamometer. The generator and volt meter are bought off-the-shelf, but the students invent their own dynamometer and construct the power generation systems. "The results are very encouraging," Sturges said. "All of the students seem to have their own way of doing things, but they are usually done correctly."

Along the way, the students learn to apply and become aware of principles of mechanical engineering. First they become familiar with the theories behind forces and equilibrium, using levers and trusses from the Erector set. Then the students move on to learning about stress and strain by making a spring, which is later used in a dynamometer to measure torque rates in the engine. The steam power plant provides a perfect basis for most of the concepts taught in the course, Sturges said. "For example, the models made it easier to communicate the principles of converting fuel energy into heat energy and then heat energy into mechanical energy," he said.

Pride Before Profits

Safety is paramount in the manufacture of miniature steam engines. That is particularly true when they are used by lay engineers, young and old. Jensen's machines are tested thoroughly to define their limits.

Actual working pressure of its commercial power plants is usually between 12 and 15 psi; a safety valve is activated at above 25 psi. Additionally, an extra pressure allowance is designed into the boilers to avoid the potential for failure. For example, the company's 5- by 10-inch boilers are tested to 450 psi.

Over the years, the company has turned down some tall orders for its engines. For example, schools in Saudi Arabia wanted to buy 30,000 of the hobby models. But Jensen, determined to concentrate on devoting his time to making machines rather than running a business, turned the order down. Some of the large commercial engines, which account for about 10 percent of the company's business volume, take between two months to one year to build.

Thomas Jensen is too concerned with maintaining the quality of his engines to be distracted by burgeoning demand. "Daddy has always done this just for the pure love of it." said Jensen's daughter Betty. "If he managed to make a living at the same time then that Was a bonus."