This is a simple single acting engine with an unusual inlet/exhaust arrangement. It runs beautifully on less than 5 p.s.i – in fact I can spin the engine by blowing down the air inlet pipe.
To be honest I was baffled as to how the engine worked in terms of controlling air input and exhaust.
Fortunately Bogs was on hand to enlighten me and I quote
“The unusual valve arrangement is done by the rigid thin piston and the offset from centre crank. The air is fed continually down the head, so when the piston is at tdc the piston lays in a normal position and is pushed out. The flywheel then takes over and turns the offset crank. Because the crank is off centre, the piston is tilted forwards at the top and back at the bottom, so allowing the air to flow past the top and bottom of the piston for the flywheel returned stroke. Once the piston reaches the end of its travel, it is then flat again, and so the outstroke takes place.”
The plans for this engine are available from John-Tom’s treasure chest of steam engine plans at http://www.john-tom.com/MyPlans/SteamPlans3/RockingSteamEngine/ROCKING%20STEAM%20ENGINEs.pdf
At the time of building this very popular engine a number of model engineers had already made their own design variation and I decided to follow suit with an ‘art deco’ look. Whilst it is clearly important to retain the key dimensions in terms of cylinder bore, piston size, crank throw etc there is no reason why you can’t get all creative and have some fun with the general cosmetics. Which is what I decided to do. So here we go with the build.
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- A start on the Rocking Engine is made by marking up a suitable length of aluminium bar for the cylinder.
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- The engine bore is started by with a centre drill to provide positive location for subsequent drilling.
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- The bore is drilled out to the required diameter of 9.5mm using WD40 as a cutting lubricant.
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- As the cylinder bore is a blind hole the depth is checked using the tang of the scale.
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- The vernier scale is used again to check the overall length of the cylinder.
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- Cosmetic cooling fins are machined into the cylinder using a parting tool.
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- The cylinder is transferred to the mill and a flycutter used to square off the four sides of the cylinder.
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- The open crank mounting area is machined following the styling of the engine cylinder fins.
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- Machining the base of the cylinder making good use of backstop for each turn of the part in the vice.
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- The art deco theme is continued with the engine mount, base and flywheel.
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- A rear view of the art deco styled Rocking engine. A novel little engine that performs well.
is the unit or measurment really cm, that would be tiny if it is.
Err, which measurement are you referring to ?
John
im not used to working in inches, is it right if i multiply all the measurments by 25.4 to get mm?
im 15 and i want to make one of these great engines. will it be easier to make a bigger scaled p one, or not?
i do not have machining tools but i have made a oscillating steam engine and it works great, will i be able to make this or does it need to be make of machined precision.
thanks john
John you are quite correct in your conversion factor from inches (imperial) to metric. When it comes to shafts and rods it is best to round up the size to available stock remembering to increase the bore of those items fitted.
I have increased the scale of a number of my engines by 50%, they are no more difficult to build and seem to run even better than the smaller ones. You will appreciate that the cost of material increases with size.
You are to be congratulated for your success in having made an oscillating steam engine without the aid of machine tools. Perhaps you would like to send me a picture of your engine for inclusion on this site ?
John
Excellent information and some good food for thought!
This engine has been on my (long!) list of projects for ages but now I’ve got it tee’d up I find that the link to the plans no longer works. Any idea if they’re still available anywhere?
Best regards
Paul
Hello Paul
Check your email – I hope this is what you are after.
John
Hi Rob
I used to struggle with getting a decent finish on my engines until I followed the advice of DividedHead given in his tutorial video. For me the most important factor is preparation of the workpiece before it goes anywhere near a polishing mop. Use superfine emery or ‘wet ‘n dry’ abrasive paper to get a mat, scratch free surface before polishing. Don’t expect the polisher to remove any machining marks. I’ve recently started using Abranet abrasive sheets 400 and 500 grade grit with good success.