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.
