The more of Elmer’s Engines I build the move I love ‘em. This time I chose his #3 engine – an Open Column which describes the appearance. The engine employs porting on the crankshaft in the same way as his ‘Standy’ engine.
My first posting on this build covers what Elmer calls the bearing which in reality is also the main frame of the engine. I had a chunk of hexagon brass bar which was machined to shape on the mill. Here’s how I did it. (Click on pics if you want to see a larger image).
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- With metric conversion calculator on hand I measured up for the bearing/engine frame.
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- The chunk of hexagon bar was cut overlength by 3 or 4 mm in around 30 seconds on my bandsaw
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- An indexable cutter was used in the first stage of squaring up my hexagon bar.
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- This is one occassion where protection against flying swarf is essential.
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- As my indexable cutter was not wide enough to pass in one sweep I switched to a fly cutter for the removal of the last few mm.
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- Using my edge finder I locate the precise edge of the workpiece. Zero my DRO, move in half the width of the edgefinder (2.5mm) zero again and that positions the centre line of the chuck exactly on the edge.
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- An end mill cutter in my mill was used to carefully shape the block to plan dimensions.
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- A satisfying afternoons work, the frame now ready to receive the drilling of airways and fixing holes.
One or two points that may give a better appreciation of my approach to building the frame.
The plan for this engine is available for you to download, free of charge at http://www.john-tom.com/html/ElmersEngines.html I always convert plan dimensions into metric using a simple chart from my Model Engineers Handbook.
Whilst the plan showed the making of the frame in two pieces the ‘chunk’ of brass bar I found in my materials stash enabled me to make it in one piece therby avoiding the need to solder. Soldering will be required later in the build and I will try to guide you through the art of hard or silver soldering when I reach that stage.
I regard my bandsaw as a vital piece of kit in the workshop. I no longer have the stamina to hack through great chunks of metal. You may notice the steps I have taken to hold short lengths of stock in the saw vice. The long screw keeps the vice jaws parallel whilst I have ‘extended’ the movable jaw with a piece of bar. Sometimes a little ingenuity is called for.
I appreciate that some of you may not have a milling facility. You can get round this to a large degree by buying brass stock closer to the finished shape and dimensions.
In shaping up the frame in the mill I usually take 0.5mm cuts when flycutting brass. With the end mill I probably advance the cutter something like 0.75mm at a time. I reckon more workpieces finish up in the scrap bin through overly optimistic depths of cut. It is sometimes tempting to take deeper cuts to speed the job along. My advice (learnt the hard way) is resist and avoid wasting hours of work.
You will see in the last picture that I have already drilled the hole for the crankshaft. I wanted to do this before milling the gap between the two bearing ends. It is particularly important on this engine to have a good, almost tight fit of the crankshaft through the bearings to prevent pressure loss. Running in will soon ease any tightness. I decided to use 5mm steel for my crankshaft which on the vernier measured 4.9mm. I selected a 4.7mm drill in the knowledge that the drilling action always produces a slightly larger hole than you might be expecting. Drill a fraction oversize can reduce all your hard work to scrap. Better to be undersize – its much easier to remove metal than put it back.
