"I Spy"

a

See-Through Steam Engine

In September of 2003 I built a "special" small flywheel as an experiment. I was so impressed by the way it turned out that I just had to build a steam engine to put it on. I built this engine "on the fly," amd am just now making "as built" plans. Here's what I came up with.

The engine has a plexiglass cylinder block, so the internal action can be observed. It will never run under steam, as probably the plexiglass would self-destruct with the heat. But it runs well on 5 to 40 psi compressed air, and I can even keep it going (for a few seconds) with lung power. (Does that make me a blowhard?) It is a single-acting engine with 1/2-inch bore and 3/4" stroke, with piston valve.

Tools used were a Micro-Mark 7x14 lathe and a Taig CNC mill. (CNC ia not required, but since I have it, why not use it?) The engine is small enough that it could be made easily with Sherline equipment.

I did not keep a logbook on this project, so I can't give you a step-by- step rundown. But I will discuss the major parts (with pictures where I thought to take them) and tuning.

Base

The base is a piece of 2" x 3-3/4" x 1/2" aluminum. I drilled the holes from the bottom so I could countersink them with a larger drill bit without changing the setup. This put the countersink exactly on target. With my eyesight (or lack of same), every little trick helps!

A miscalculation in dimensioning led to the countersink in the lower right overrunning the edge of the base. Luckily, this is on the bottom of the base and when the engine was assembled the flywheel hid it from casual inspection.

Cylinder Block

The nice thing about plexiglass is that you can see through it. Unfortunately, this feature is a disadvantage when you're trying to take a picture of it. My camera "saw through" the plexiglas to focus on what was behind it. Even when I tried to focus manually it gave me fits; hence, no picture. But the plans in .pdf show how to make it.

My only advice on making the cylinder block out of plexiglass is to use sharp tooling and run slow. Dull tooling or high spindle speed will overheat the plexiglass and ruin the piece. Don't ask me how I know. This engine will never be run on steam, as I suspect the heat would destroy the cylinder block. Knowing this, I used Loktite in much of the assembly. I found the plexiglass at Boeing Surplus in Seattle, Washington. From the piece I got for a dollar I could make a couple of dozen of these.

Air Intake Nipple

The air intake nipple completes the power end of the engine. It's made of 1/4" brass round, and is 1" long. The size of the hole running through it is just large enough to accept the tubing that comes with a can of Endust -- a source of compressed air intended for cleaning computer keyboards and such. This is an excellent portable air source for demonstrating the engine away from a compressor.

Piston/Wrist Pin

It's important to make the piston after doing the cylinder block, so you can turn it down to a slip fit within the cylinder. Doing it in reverse order, for me, is making it for the trash bin. The wrist pin is made of 1/8" steel round, shorter than the piston diameter, with each end rounded and smoothed, to avoid scoring the cylinder.

Piston Connecting Rod

I forgot to take a picture of the piston connecting rod, but no matter; you can see it in the pictures of the assembled engine at the beginning of this page. It's just a straight (more or less) piece of brass with a hole at each end for attachment to the piston and the crank. You'll notice it has a "jog" in the middlle. This was to cover a mistake in alignment between the cylinder and the crank. (I made this engine "on the fly," remember?)

Valve

The valve was made from 3/16:brass round, picked up from a local hardware store. It was just enough oversize to not fit in the cylinder block; I had to shave it slightly in the lathe to provide a slip fit. I drilled and tapped 2-56 the hole for attaching the connecting rod. The screw shown is a 2-56 x 1/4". You could use a smaller, untapped hole with a brad running through it, but though that works, it's unsightly. The groove on the right was made with a hacksaw, with the workpiece turning in the lathe. That allows air from the nipple into the steam passage for the power stroke. The flat on the right allows air to escape on the return stroke.

Valve Connecting Rod

The connecting rod for the valve was a natural for CNC, and that is how I made it. Before I had a CNC mill, I made them with a step drill, a coping saw and a file. That worked ok, but it took a lot longer. With CNC, I just drew the part and let the computer direct the mill to cut it out with a 1/8" end mill. Aint technology grand?

Bearing Block

This is another piece I made with CNC. It could as easily be made with a hand-cranked mill. The piece is made of brass, powder-coated in green. I drilled the hole for the crankshaft clear through, and then milled out the center. This ensures that the two holes are precisely in line, preventing the crankshaft from binding. I installed the 1/4" bronze bushings, then ran a piece of 1/4" steel round through them to ensure alignment, and Loktited them in place. Not seen are two holes drilled from the bottom into the columns for mounting the piece to the base.

Crankshaft/Crank

The crankshaft is a piece of 1/4" steel round, cut to length as shown in the plans. The crank is 1/8" aluminum turned to 1" diameter with a 4-40 tapped hole 3/8" off center. This provides a 3/4" throw for the piston. The crank is too thin to accept a setscrew, so (knowing this engine will never see steam) I used Loktite to attach it to the crankshaft.

Eccentric

The eccentric was made from 3/4" steel round, turned down to 11/16" and a 1/8" portion further turned to "just a skosh" less than 1/2", to provide a slip fit on the valve connecting rod described above. This needs to be a fairly close fit; too loose and you have sloppy action of the valve, causing erratic operation of the engine; too tight and you have binding, with no operation of the engine. Not seen in the photo is a setscrew to bind the eccentric to the crankshaft. Do not put a flat on the crankshaft to accept the setscrew, as you tune the engine by adjusting the eccentric. Note the rough surface on the face of the piece. That's what you get when you let your tool get dull. I have since cleaned that surface up with a file.

Spacer/Retainer

This piece butts up against the bearing block to prevent the valve connecting rod from slipping off the eccentric. It also serves to prevent friction between the eccentric and the bearing block. I made the hole 1/2" diameter to fit over the 1/2" portion of the eccentric. Turns out I needn't have bothered, for it doesn't stay in that position anyway -- and doesn't need to. I could just as easily gotten away with a 1/4" hole to accept the crankshaft. The piece is 1/16" thick, just right to position the eccentric in line with the valve.

Flywheel/Hub

This is the part that inspired the whole engine. I have a detailed writeup on its construction at --

http://www.davegoodfellow.com/flywheel.html

-- so I won't repeat it here. I made the hub for it later, and that is a tale of woe. I intended to secure the flywheel to the crankshaft with the hub and a screw into a tapped hole in the end of the crankshaft. To make that work I needed to install some sort of retainer for the flywheel to butt up against. I tried a C-ring, but it would pop out of its groove before I could tighten it enough to make the flywheel rotate with the crankshaft. Having a "Senior Moment" at the time, it didn't occur to me that I could put a steel pin crossways in the crankshaft; that would have been plenty strong enough to let the hub tighten down. And if I put a corresponding notch in the inside ring of the flywheel, the hub would not have to be super-tight anyway.

But Senior Moments will not be denied, and I was tired. I stuck the flywheel on with -- you guessed it -- Loktite. Hopefully, I'll never have to dismantle it.

Tuning

Tuning this engine is much easier done than described, but here goes:

1. Rotate the flywheel in the intended direction of operation, until the piston reaches "bottom dead center" -- that is, its furthest travel into the cylinder.

2. While holding the flywheel in this position, loosen the setscrew on the eccentric and rotate it until the "air input" groove (the one made with the hacksaw") just begins to line up with the hole that goes from the input nipple through the valve cylinder and into the piston cylinder. This is easy to do with the plexiglas cylinder block, as you don't have to squint through the hole; you can watch it from the top of the block.

3. Retighten the setscrew.

Tuning is completed. Put five or ten pounds of air to it, flip the flywheel in the intended direction, and watch it go. In spite of all the compromises, it's a sweet-running, attractive little engine. After running it for a half-hour or so, I was able to make it go (barely) by blowing in the input nipple.

Click here to see it run.

Plans

I have completed "as built" plans, which have been uploaded in .pdf to --

I Spy Plans

I hope if you decide to build this little engine you'll have as much fun with it as I did.

Other Machinists' Versions

Michael Lam, 14, of Ottawa, Ontario, Canada, built "I Spy" as a 9th grade Science Fair project. As you can see from the photo at Lam.html, his project was successful.

Jerry, 65, of Rancho Cucamonga, CA, built this nifty version mostly out of wood. He lined the cylinders with brass tubing and made some other parts from metal, but much of the project shows his woodworking skills. Not satisfied with just watching it run, he gave it work to do, in the form of a small generator and light post. Photo at Jerry.