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Double Oscillator

Making a start. The pillar and base were machined to size and ready for further detailing. It is not essential to shape the pillar as shown - a simple, more easily formed, rectangle would do just as well.
It may look like a memorial stone but download the plans and it will make sense. The pillar and base were machined to size and ready for further detailing. It is not essential to shape the pillar as shown – a simple, more easily formed, rectangle would do just as well.

April 6th 2010

Here’s a small model steam engine which is an ideal first project for the newcomer to model engineering.

Whilst I have been extolling the virtues of Elmers Wobbler as a good starter project this engine is just slightly more advanced in that it is a double acting oscillating engine rather than a single which is the case with Elmer’s Wobbler.

With a single acting engine the steam (or compressed air) powers the piston in one direction only and relies on the flywheel to carry the piston through to the top of the next stroke. With a double acting engine the steam is also used to power the piston back. All that is required is to provide an extra pair of ports at the opposite end of the stroke and seal off the base of the cylinder whilst allowing the piston rod to pass through it without allowing the pressure to escape.

Making a start

So, first things first. Download the plans from http://www.john-tom.com/html/SteamPlans.html Scroll down to ‘Model Steam Engine Plans – Page 1′. Just below you will find ‘The first steam engine I built is Here – a good first engine’. This link will take you to a downloadable set of very clear well dimensioned plans in metric.  Whilst I am a great fan of Elmer’s engines I am aware that some beginners find the mixture of imperial fractions and decimalised dimensions a little confusing at first.

On looking over the plans two things might concern you, particularly if you haven’t invested in a milling machine at this stage. First the main column features stepped sides, which does add a certain something to the styling. If you prefer to keep things simple this main column can be left as a 105 x 60 mm rectangle.

You will also see that the base has a cutaway well for the lower part of the flywheel. If, like me, you like the idea of the well and you are working without a milling machine then you could make the base in two layers. The opening on the top layer could be cut right through by chain drilling and filing. The two layers could then be bolted together from beneath using four M5 countersunk screws. If you don’t fancy that suggestion you could simply raise the crank shaft hole and porting so the flywheel clears the base without any unecessary machining.

Choice of materials

My advice is to work in brass for the cylinder and flywheel and aluminium for the base and column. Items such as crankshaft, crankwheel and  piston can be machined in free cutting stainless steel. One possible pitfall to be wary of is the drilling of the steam passageways in the column. Without care it would be all too easy to snap off a drill during this delicate operation which would mean all your hard work in fashioning the column would be wasted – more on this later. I mention it here to support my suggestion to use aluminium rather than steel.

I usually prefer to start by making the base and pillar. In other words the basic framework on which the other components are added. Lack of suitable material for the base decided me on making the pillar first. I have shaped this pretty much to plan using my milling machine but, as I said, a plain and simple rectangle would do the job just as well. By using a backstop on the vice it was a simple matter to shape one side of the pillar then flip it over to mirror the milling of the first side.

My local monthly autojumble at Rufforth was on this morning and there are always a number of model engineering tool and material suppliers in attendance so a piece of 12mm aluminium plate was aquired. I cut the plate to size using my hand held Black and Decker jigsaw and plenty of WD40 as a cutting and cooling agent. The two plates were drilled and tapped then bolted together to give me a total depth of 24mm and the edges milled square and flush. The next stage will be to machine the well, or cutout, to provide clearance for the flywheel.

April 14th 2010

A little bit of progress over the last week.

4 comments to Double Oscillator

  • Appreciate the recommendation. Will try it out.|

  • Dave

    Hi John. Are the plans for this engine still on john’s website? I cant seem to find it. Also have you had an experience with taig / peatol lathes? From the research Iv done they look like they would cope with this sort of project. I cannot afford a mini lathe at the moment so i’m looking for something just to get me started as I have no experience at all. Thanks Dave

  • Hi John
    Great site, have been following quietly for a couple of months. Glad you introduced me to these little engines, I will have to have a go. They look like something that my attention span will cope with. Are there larger versions of the pictures, having difficulty with the detail. I notice that others seem to open up but those for the Double Oscillator seem just to refresh the page. Have just added a blog to my site and yours is one of the first links in my blogroll.
    Cheers
    John