Double Acting Oscillating Engine

double acting oscillating engine

This double acting oscillating engine started when I bought the Warco WM240b and I wanted something substantial to make and the idea of a large rather agricultural oscillating engine popped into my head.

The original intention was that it would be a one piece quarter inch thick steel plate that everything fixed to, but even the 240b would have not had the necessary swing….or maybe just.

Specifications

  • 15mm bore
  • 50mm stroke
  • 147mm between centres (cylinder pivot and crank bearing
  • Cylinder
    • Cast iron block 65 x 30 x 30mm
    • Port centres 6mm in from ends of cylinder 2.8mm diameter
    • 1/2 inch (12.7mm) mild steel pivot in centre of cylinder
    • Brass bearing
  • Flywheel
    • Geared 2:1 from crankshaft
    • 62mm diameter 18mm wide
  • Conrod
    • 3/16 inch silver steel
    • Big end ball bearing
    • 151mm from centre of big end to top face of PB piston
  • Crank
    • 10mm shaft running on 2x ball bearings
    • 8mm hollow big end pin
    • 25mm crank throw

The spring and nut that applies the force to the oscillating cylinder and so keeps it in contact with the main body of the engine that forms the valve chest.

The copper pipe feeds the steam inlet at the top of the action and the exhaust is just a hole in the 1/4″ plate (you can see one of these under the copper pipe).

A simple piece of hex brass machined and drilled to turn it into a T-junction for the steam inlet.

The 5/32″ copper tube was soldered in one go to the T-junction and the man body of the engine.

The cylinder was machined from a solid cast iron square section.

A piece of thin brass was bent over the cylinder and then drilled and tapped 8BA.

The main bearing block was machined from a piece of aluminium with 5 brass bolts fixing it to the main engine backbone.

In the bearing block I fitted two ball races, one of which was a very nice tight fit, the other was there, but not quite. The fall back was some TruLoc 268 – what a saviour.

Although this engine is rather crude I did remove some of the mass from the crank pin. I drilled the hole and then turned the pin around to machine the other side. This is always tricky as it is so easy to crush thin walled parts in a 3-jaw chuck or leave score marks when it rotates. I solved this problem by using the ER25 collets in a chuck that was then fitted to the normal 3-jaw.

The slots in the 1/4″ plate were machined using a Soba Swivel Vice to get the angles.

The engine has a small flywheel that is running at roughly 2.5x crank speed. The original intention was to feed the waste exhaust onto the flywheel – I never got round to this. The brass gear was machined to make it look lighter.

This engine needed a bold colour. At first I thought blue, but then someone said to me red – so a search of the spray paints at Halfords and I came out with a bright Ford Rosso Red…

The cutouts were lined in red, a lot of masking and then finally cleaning any overspray to get a crisp finish.

The plinth was oiled and polished oak with bog oak ends and feet.

Finally, a pre-painted version of the Double Acting Oscillating Engine running in the workshop.

As you can see in the video, this engine started as a simple oscillating engine with a large flywheel and then morphed into a geared smaller flywheel version. I think the final version is more unusual and pleasing. More designs in the gallery page.

About Nigel 355 Articles
I've been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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