Elmer’s ‘Tiny’ #23
Jim Greethead from New South Wales enjoying a pint of amber nectar at the Bristol Model Eng Exhibition during a recent visit to the UK.
Jim's trio of beautifully built 'Tinys' each fed with air from a neat three way manifold. I think Elmer Verburg would have been well pleased.
As soon as I heard that ‘Aussie Jim’ was building Elmer Verburg’s #23 ‘Tiny’ I asked Jim if he would consider taking some step by step photographs and prepare write up notes on his build procedure. The following is the result.
Jim was recently over here from his home in Bywong, NSW, Australia and made a point of visiting the 2009 Model Engineering Exhibition in Bristol.
Thanks Jim, this is a first class article and introduces a number of innovative solutions to problem solving from which we can all learn - so over to you Jim for the full story……….
Building Elmer’s ‘Tiny’ Engine
When I saw the Elmer’s Tiny that John Somers built, I knew that I just had to have one. This story is not a tutorial or an instructional article, it is just a few photos and a couple of things I learnt on the way.
The first task was to convert Elmer’s drawings to metric to suit my workshop. This involved DesignCAD and quite a bit of learning. It would have been faster on the back of an envelope but I need to learn DesignCAD anyway. You can see a couple of pencil changes to the drawing as it appears in the photos but it was good enough to work with.
The next decision was whether to make it in aluminium (my favourite material - easy to work and it is clean), or brass (looks good but is expensive and the finished engine needs polishing ) or stainless (hard to work and the only available piece of unknown origin). It seemed easier to make three then to decide between them and, as everyone knows, it is just as quick because the setup time is shared. Mind you, I think “everyone” knows this from theory not from experience.
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- Not having a form tool or ball turning tool....
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- ...I used a chainsaw file to form the grooves.
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- Elmer's drawing shows the bit where the crankshaft goes as being spherical so on the aluminium engine, I rounded it off with a flat file.
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- But on the others, I just left it cylindrical and I am happy with the result.
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- Then I buffed them so the buffing would not round off the edges of the subsequent machining. Buffing can hide a multitude of sins (and tool marks).
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- So now I had three bodies ready for the next step.I actually left them on the stick until they were finished and running. They are easier to handle like that.
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- For machining convenience, I dimensioned the body from the top end , set an x axis stop and then established both x and y zeros.
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- A handy bar of 38mm brass was sufficiently accurate for finding the y axis zero.
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- The 19mm bar fitted nicely in the slots, needing only a couple of clamps to hold it.
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- After that, the flat was machined and the holes spotted and drilled (and deburred) for the cylinder pivot and the crankshaft bearing.
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- Then came the ports. Elmer's drawing shows the ports being #57 drill which equates to about 1mm. After a couple of calculations, I increased this to 1.2mm and then to 1.5 when my last 1.2mm drill broke (in the hole).
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- The 1.5 gives some overlap but that doesn't matter-it just wastes a bit of air (and that's free until they find a way to charge for it).
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- I also calculated the position of the ports instead of using Elmer's gizmo.
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- The next bit was interesting! Leaving the x axis lined up with the ports, I rotated the body left and right and drilled the inlet and exhaust connections (I made them symmetrical).
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- I found that I needed to set a stop where the drill just breaks through into the port hole because the drill tends to grab and wind itself right through to the other side and then it is back to square one and start all over again.
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- One more rotation to relieve the pivot hole for the spring. I used a drill in the pivot hole to line it up.Once the crankshaft bearing hole is deburred, the body of the engine is finished.