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Steam engine from scrap metal

I had a block of brass but no mill, no casting, and want to design my own steam engine

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JasonB20/11/2020 07:26:38
20955 forum posts
2331 photos
1 articles

valve at 1/4 dia of main cylinder or even a bit less would be my thoughts

Yes lap valve

Piston bronze or aluminium, one O ring per piston

They are referred to as glands not bearings but can have packing or O rings

"Heads" or cylinder covers on either end don't want to leak, this is a double acting engine so both sides need to be pressurised in turn by steam which will drive the previous spent steam out of the exhaust on the opposite side of the piston.

To fill your passages and get rid of some of the dead volume you could loctite a plain 6.5mm rod into the hole that has had a flat machined down one side before inserting.

For an idea of size this although a single acting engine has a 24mm dia piston, the valve is 5mm dia overall 3mm dia at the waist. Pasages are 3mmdia and the 4mm OD PVC hose probably has a bore of 2.5mm or less.

Edited By JasonB on 20/11/2020 07:27:37

Turbine Guy20/11/2020 21:26:15
375 forum posts
210 photos

Hi Evan,

I agree with all of JasonB's comments. Unless you plan to operate your steam engine at a high speed (which I suggest you don't do), a small piston valve will work fine. To prevent getting yourself in a bind, I suggest you look at some of the drawings available in ME like the Example Drawing. This will give you an idea of the proportions of the parts, how they fit together, and examples of methods for making difficult parts. In this example, a method of making the double throw crank shaft is about as simple as I have seen. I will leave suggestions for machining up to others on this website that have far more skill and experience.

Good luck with your engine,


Evan Lewis20/11/2020 22:16:40
23 forum posts
10 photos

Thanks to you both again. Last night I threaded an 8mm brass bar, tapped the passage hole and glued it in with superglue. I considered cutting a keyway groove down the side but decided to drill it afterwards. we will se how that goes! I like your idea of a plain rod with a flat on the side best. I still have 3 more to do so I will try that. Yes, the link should be very helpful.

I don't have the material for the crankshaft yet. I would like to make it from stainless so that it doesn't rust. It is much harder to work with. Am I asking fro trouble?

Nigel Graham 220/11/2020 23:14:37
1618 forum posts
20 photos

You could use a free-cutting grade of stainless-steel for the crankshaft, yes, though you would still have to approach machining it with due care for its characteristics.

In practice though, crankshafts don't usually go rusty because much of the metal is covered by oily bearings, but a simple wipe over with an oily cloth after use should protect the exposed webs for a reasonable time.

Turbine Guy21/11/2020 16:36:40
375 forum posts
210 photos

I wouldn't hesitate to use carbon steel parts. If you wipe them over with a oily cloth like Nigel suggested or spray them with WD40 like I do after each run, they can be rust free for quite a long time. The following photo is my Chiltern steam engine that hasn't been run for months. The base plate, crankshaft, bottom cover plates, columns, slider tube, and fasteners are all unpainted carbon steel. The plate the engine is mounted on is stainless steel. I originally planned on painting most of the carbon steel parts, but Chiltern did such a nice job on the finish, I liked the appearance of them unpainted.

Chiltern 1

Evan Lewis22/11/2020 12:29:17
23 forum posts
10 photos


Does that look better? I tapped the steam passage and redialed it, reducing the size from 8 to 4 mm and thus reducing area and volume by a factor of 4. I hope it works better.

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