Thumbnail 3 Cylinder Steam engine

Mini 3 Cylinder Oscillating Steam Engine

This small oscillating steam engine with three cylinders is perfect for use with a small lathe. I built it on my Emco Compact 5. The machine has three cylinders with a diameter of 6mm and a stroke of 12mm. It is particularly well suited as a beginner’s project because the parts are comparatively easy to make. A reversing valve is integrated, which offers the possibility to change the direction of rotation of the machine. A servo can easily be connected to this valve to control the direction of rotation via a remote control. This machine is well suited for use in small boats.




Technical data of the 3 cylinder steam engine
Technical data of the 3 cylinder steam engine

Cylinder of 3 cylinder steam engine

As already mentioned, the machine consists of three cylinders with a piston diameter of 6 mm and a piston stroke of 12 mm. The cylinder barrel was expanded with a 6H7 reamer. The surface of this bore was carefully smoothed after brazing with abrasive paste and a piece of hardwood to obtain the smoothest possible surface. A smooth surface is critical for a good seal of the piston in the cylinder.

The mirror surfaces of the cylinders were clamped into the four-jaw chuck and precisely machined to ensure they were flat. In the same setup, the M3 threads for the mirror axes were drilled to ensure that the mirror surfaces and axes were exactly square to each other.

The curvature of the mirror was made with a homemade milling cutter. The mirror was fixed in the vise while the router bit was clamped in the jaw chuck. The desired rounding was then milled out at a slow feed rate.
Finally, all parts were soldered with silver braze.

The crankshaft bearing of the steam engine

The manufacture of the crank bearing is a demanding task due to the tiny components. First, the parts are carefully marked and center punched. Then the basic shape is carefully filed out with a needle file. Next, all the necessary holes are drilled, and then the bearing is divided into two separate parts.

The threads are drilled precisely and the parts are screwed together. After this step, the screwed crank bearing is clamped in a four-jaw chuck, and the bore is carefully machined with a reamer. In this way, a divisible crank bearing with an exact fit is created.




The crankshaft

The cheeks of the crankshaft are first carefully marked and center punched before drilling begins. First, a hole is drilled through which all four parts will later be screwed together. This is followed by drilling the second hole. This ensures that all the holes fit together exactly.

Then the package of crankshaft cheeks is clamped in the lathe and machined from all sides to ensure that they are all the same size. In this way, four parts are created that are exactly identical.

The crankshaft is then assembled. Holes are now drilled through the crankshaft cheeks into the shaft. Metal pins are hammered into these holes to securely fix all parts. After that, the soldering of the crankshaft takes place. After soldering, the continuous shaft is cut off, and thus the crankshaft is completed.




The piston

The manufacture of the piston should not cause any major difficulties. The piston is made with an oversize and then soldered to the piston rod. To ensure that the piston is soldered as centrically as possible to the piston rod, I made a simple jig out of aluminum. This jig is made of a round material with a hole in the center. A look at the pictures should illustrate how this works.

The piston is now soldered with the help of silver solder. After soldering, the piston is clamped in the lathe and face turned. To ensure that the piston is exactly centered to the piston rod, machining is done lengthwise to achieve the correct diameter.

The piston is then adjusted to the piston tube using very fine sandpaper. Here it is important to check regularly that the piston fits well in the tube. Finally, a ring is made that serves as a seal. The oil collects in this ring, effectively sealing the piston.

However, I have built another piston. This consists of a Teflon piston. Teflon has the advantage that it has excellent sliding properties. In addition, Teflon is temperature resistant which makes it an ideal material for pistons. If you have the possibility to get Teflon I would prefer this piston. Here you can try something that works best.

Drilling the steam holes

This step in the construction of the 3-cylinder steam engine is among the most important. The cylinder oscillates around the cylinder axis, with steam being fed into the cylinder at one of the turning points and steam having to be expelled from the cylinder at the other turning point. For these operations, precise matching of the steam bores in the cylinder and in the fixed mirror is essential.

Therefore, the assembly of the machine takes place and it is brought into one of the end positions. A mark is then made through the hole in the cylinder on the fixed mirror. Then the cylinder is rotated to the other end position, and again a mark is made. This process is repeated for all three cylinders. Thus, a separate mirror is made for each cylinder. In this way, the steam holes of the cylinder now match the holes in the fixed mirror 100%.
The hole in the cylinder must be sealed afterwards, of course. This is best done with a soft solder to prevent the cylinder from being deformed by the heat input.




The steam pipes

Copper tubes are used for feeding and discharging steam into the machine. To bend these tubes, I constructed a small bending aid that allows the tubes to be bent without kinking. In order to solder the steam feed pieces to the tubes, the machine must be fully assembled so that everything is in its final place. The steam supply pieces are then screwed together and the steam pipes are inserted.

Thus assembled, everything can now be soldered in its installed state. Here, it is crucial to protect the machine from excessive heat. For this purpose, I wrapped the machine with wet paper and aluminum foil. This ensures that soldering can be done to the leads without damaging the mirrors with too much heat.




Switching valve

The direction of rotation of the 3 cylinder steam engine can be changed with the changeover valve. Its operation is shown in the pictures. Inside the brass block there are holes through which the steam is directed. Through the switching mechanism, the steam is alternately fed into the main lines of the machine. Depending on how the lever is set, the steam either flows through one line while the exhaust steam is discharged through the other steam line, or vice versa. This mechanism allows changing the direction of rotation of the steam engine, which is crucial for its functionality.




Final work

To finish the machine and give it an attractive appearance on the outside, a few more work steps are required. Some parts were treated with a burnishing liquid to blacken them. The longer the brass parts are left in this liquid, the darker they become. This creates a really nice effect.

Furthermore, the steam lines were wrapped with cotton string and Teflon. This not only has aesthetic benefits, but also acts as a thermal insulator and prevents the steam from condensing in the lines.

Some parts were sandblasted using a homemade sandblasting booth. This booth consists of a simple wooden box with two arm openings and a glass panel on top to see inside the box. The air gun was equipped with a T-piece. A small hose was attached to one end of the tee, which was immersed in the sand. The principle of the „Venturi effect“ creates a negative pressure in this hose, which sucks in the sand. It is important to cover all threads with tape to protect them from damage.




The finished 3 cylinder steam engine

You can download the building plan here:

You will get the following digital files:
  • All drawings needed for construction in .pdf and .dxf format.
  • The complete 3D model of the Steam machine in .step format.
  • An instruction video with all building steps.
  • I will do my best to help you with any problems or questions.

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