Steam Power!

Just wanted to share the small steam engine I have been building in the machine shop:

Steam engine, as it was last month, without reversing gear
Today’s first trial fitting of the Stephenson reversing gear

(fingers crossed…new photo place since the Photobucket debacle).

I have between 40 and 50 hours of machining work in the engine and the Stephenson reversing gear, and it is almost done. The reversing gear is still incomplete–I need to de-burr and polish the parts and pin some things together.

It’s a Stuart model 10V, built from castings purchased from Stuart in the UK.
The engine is tiny, about 6 inches tall with a 5/8" cylinder bore.

One of these days I’ll get around to posting a “Ask the home shop machinist” thread, and see if it gathers any interest.

Looks to be very nice work.

Back in the 50’s I had a model steam engine that burned solid fuel tablets, but of course I’d not built it. But fun to play with anyway.

I’ve attended farm toy shows and there are sometimes folks there with model steam engines that they run on compressed air because the show doesn’t allow open flames. Maybe they could use an electric boiler.



Like those guys, I run my steam engines on compressed air. For me the most enjoyable part is the process of hand crafting every single part–once the engine is complete it joins its brothers on the shelf.
Some day I may make a boiler, but it would still be about the process of making (sharpening skills in silver soldering and such).

Way cool! That is some fine machining.

Those look good!

I am curious, does the reversing gear basically just reverse the inlet & the exhaust of the steam engine?

Nicely done. Few understand the time it takes to not only make something like that work, but look good as well.

My father and I built the Coles Power Models American LaFrance steam fire engine, finished a little over a year ago. I will have to figure out a photobucket account and post pictures. Better than 2000 hours of machining time, and probably $3000 in castings and fittings. I haven’t fired the boiler, although it’s been hydro tested to 175 psi. I fear the boom of the boiler deciding it doesn’t want to play. It’s been run on air a number of times (It’s also illegal for me to fire the boiler in Massachusetts, as I don’t have a Class 1 Fireman’s license - Rhode Island is ok, though).

I know the pride of running a steam engine you made with your own hands for the first time. It’s a great feeling. Sadly, it’s also addictive - I have had my eyes on a Corliss engine for some time, but too many other projects get in the way.


A friend built a steam engine from a kit. He had to make three crankshafts–kept screwing up–but he finally got it done and it ran fine (on air). Far beyond my ability or patience.

I looked up Coles Power Models, and it appears that they closed up shop this year. To bad.



To answer your question, this reversing gear is not reversing inlet and exhaust–it is changing the valve timing.

On the front of the original steam engine photo you can see a single eccentric cam with a brass eccentric strap around it. That strap connects to a sliding valve in the valve chest at the top of the engine (the box with “S” on it).

In the original engine, the setup technique is to set the piston at TDC and rotate the little eccentric cam 120 degrees to the left and snug it down. That is the correct position for running the engine clockwise when viewed from the flywheel.

The reversing gear adds a second eccentric, shown here, which is pinned to the original eccentric at 120 degrees.
At the bottom of this view of the reversing gear you can see two brass eccentric straps stacked on top of each other, with steel rods going to opposite ends of the curved part.

The brass straps are attached to the two-piece stack of eccentric sheaves (the original from the first engine, plus the newly made sheave pictured above). The stack of sheaves forms a two-lobe cam shaft.

At this point it should be clear that each sheave will move its corresponding end of the curved part up and down independently, resulting in the curved part performing a rocking motion.

Now consider the lever and linkages. All that does is select which end of the curved part is inline with the top valve linkage. Flip the lever up and the curved part slides to the left, and the valve receives input from the rearmost eccentric, the one positioned 120 degrees clockwise from TDC.
Flip the lever down and the curved part slides to the far right, the valve receives input from the front eccentric, the one positioned 120 degrees CCW from TDC.

Yes, it took a while for me to get my head around that. The exploded diagrams provided with the kit are excellent, but one must see it up close and personal in order to really get it.

Indeed. I love doing this work because I can finish my regular job, have dinner, and then go look at the plans and see what part I want to make that evening. It’s a soothing process; there is something quite satisfying about creating parts with an accuracy down to the nearest thousandth of an inch (.025mm).

Now I want to see that steam fire engine of yours!

And I can definitely believe 2000 hours went into it. Each part is typically a one-off, and there is usually a little bit of a learning curve to certain odd parts (hmmm… do I want to do this in the 4 jaw chuck, or on the mill. Which sequence should I do the operations…)

Even something as simple as the eccentric sheave from the last post takes an hour or so to machine.

I can’t say I’m surprised. Customer service was not their strong suit. I waited over nine months for a boiler water gauge glass. Not the glass tube, the mounting hardware and valve that the glass sits in. They kept telling me they’d get around to making them.

I wonder what happened to the casting patterns. The folks who (recently) owned Cole’s got them off of the original owner. The loss of those would be a tragedy for the model engineering community.

Patience is often the key here.
My wife looks in awe at some of these little bitty parts and says she would never have the patience to do this.

Here are two tiny bolts that I made last week from 12L14 steel:

Tiny Bolts

Here’s the steps it took to make those little things:

  • Facing a hunk of 3/16" 12L14 steel rod on the lathe in a collet
  • Turning a .156" length down to .100 (for 7BA threads)
  • Undercutting the base of the bolt to .081 (minor diameter)
  • Running a 7BA die down the bolt
  • Taking a cut on the tip of the bolt to thin it to 1/16" for a short distance
  • Mounting the rod stock in the milling vise in a hexagonal collet block
  • Milling 6 sides to .172" across flats, flipping the collet block one flat for each pass.
  • Remounting the collet in the lathe
  • Chamfering the underside edge of the bolt head prior to parting it off
  • Parting off the bolt from the stock .062" from the threads (creating a 1/16" thick head)
  • Flipping it around in a 3/32" collet and facing the bolt head
  • Chamfering the top side edge of the bolt head
  • Polishing the head with sandpaper

Some of those steps were performed quickly, in sequence, without even thinking about it, while others involved several minutes to change the setup and work out the best execution plan.

Here you go:

Very cool, and worth every hour of effort.

(it was worth dealing with Photobucket’s annoyances in order to see those beautiful shots).

How big is that thing? I see so many parts that would tax a home machine shop’s capacity.

Unless you and your father have access to a production machine shop, it would be a challenge to turn some of those parts on a home machinist’s lathe. Likewise, the castings look big enough to exceed the capacity of even a full-sized Bridgeport mill.

Overall dimensions are 9" wide, 18" tall, and 28" long. Weighs 68 pounds with an empty boiler. It’s hefty. Definitely not the first model one should build.

My family owns a machine shop, so you’re not at all off with that statement. I was sweeping floors there at 8 years old, and knew how to run a lathe by 11. Spent 8 long years there before setting off in my own happy direction. The steamer had been a very long term dream of mine, and my father was coming up to his retirement time. He was looking for a project to whittle away at, so I was happy to pony up the cash for castings. Series 1 CNC Bridgeports, and some fairly good sized lathes were critical - I’m not sure it would have been built without production level machines. The tooling alone must be thousands of dollars, let alone the machines themselves.

Really, the boiler was the biggest pain. To get it hot enough to silver solder one spot would melt the solder in another. It was a troubling trend of chasing your own tail all around the boiler. We ended up having a very skilled friend weld the copper innards (it’s a fire tube boiler, not water tube). The fittings, stays, and other penetrations into that boiler were a nightmare. And you can’t plan it out ahead of time, everything depends on the location of everything else, so there’s no reference point to start from.

I’ve talked to people who have built boats as a hobby project. They all say everyone should build a boat, because once you build one, you’ll never build another one. I love steam fire engines, and steam in general, but I’m never building that model again!

Finally got around to posting a few more shots here…

This is what a Stuart 10V kit looks like when it comes out of the box:
Drawings with Rough Parts

Some parts are rough castings that need a few hours of machining of various surfaces, drilling and tapping holes, boring holes, and such.
The A-frame piece on the left is a good example: lots of finishing, a 5 bolt circle at the top, and a precision bore to guide the crosshead.
Similarly, part 38 is a bit of cast red brass that is intended to be sliced up into two bearings, bored, bolt holes drilled, and finished on multiple faces.

Other parts are simple bar stock that needs to be machined into submission. For example, both of the heads of the engine are machined from that piece of iron round stock on the right side of figure 2.6.15. The piston and gland were both machined from that hunk of brass bar stock on figure 8.

Here’s a shot of the original kit for the Stephenson Reversing Gear:
Stephenson Reversing Gear Kit

You can see that for that kit they provided several brass bits that are all but done. Indeed, you can see the brass lever in almost perfectly finished condition, needing two holes to be drilled.
In my opinion, they took a little bit of the fun out of the kit by doing this, but it took long enough to make anyway–making tiny fasteners out of brass consumed quite a bit of time.
They are somewhat stingy with material, and half of the time when I am working on a piece of cold rolled steel or brass bar stock I’ll just grab a piece from my scrap drawer in order to have something to grab on to.

A shot of the preparation of the brass straps for the eccentrics

Most of my milling machine work is done by following the numbers on the DRO (digital readout), a godsend for machinists, but I still enjoy going to the surface plate to scribe layout lines on Dykem blue.