Start Model Engineering

After a 3 month haul making my Beam engine I wanted something less demanding and finally chose Elmers #19 Standby engine which is an interesting variation on the ‘wobbler’ engine in that the cylinder doesn’t wobble ! (although it may on mine !).

Bogsie introduced me to the concept that if you are making one engine you may as well make two, three or even half a dozen as most of the time is spent on setting up and once you have done one its only a moments job to make another one (or two). Yeah, right Bogsie.

I started by cutting three ‘blanks’ of 1″ x 2″ chassis plates from 1/4″ thick aluminium and bonded them together with superglue before milling them as one down to final size.

Incidentally I found my Black and Decker jig saw ideal for hacking through aluminium plate – change blades frequently and lubricate with lashings of WD40 and save yourself the effort of using the hacksaw. I then machined down to final size on my milling machine

After using the flycutter to trim the block of three chassis plates down to size the next job was to drill the various holes. Everything was going well until I had to drill along the arm of the chassis with a 2mm airway aprox 1 1/2″ long. With care I managed the first two then on the third I snapped a drill leaving the broken bit embedded in the chassis. So, I now have to remake a third chassis plate. It was at this stage that I abandoned the workshop and sought solice in a cool beer in the warm sunshine.

More next time

Sooooo, I set to and made a third chassis plate then went and messed that up. It was at this point that I decided to cut my production run from three down to two.

Click here for page two

On to the last lap with this Elmer variation. The cranks were machined out of stainless using plenty of cutting oil. I picked up a litre bottle of cutting oil from Machine Mart and as I work mainly in brass and aluminium the oil is lasting me a long long time. Turned the stainless down to size on the lathe then transferred to the mill for cleaning up. I always seemed to find that when parting off two things happen. The cut veers away from the face of the machined part and there is often a protrusion remaining as the parting tool breaks through. Both these unwanted formations can be cleaned up easily in the mill and then on to forming the web. An M3 screw with a shoulder to act as the bearing surface for the ‘big end’ of the con rod was machined up.

Next on the ‘to do’ list was drilling and tapping the back of the cylinder for attachment to the engine frame taking care not to drill through into the cylinder bore – 4mm seemed about right. Where possible I use a guide block to ensure my tap runs square to the hole. You can also replace your drill bit after preparing the hole to be tapped with the appropriate tap and turn the chuck a few turns by hand to get the thread started and running square. This can then be transferred to the vice for finishing off.

The next stage I am afraid didn’t get covered photographically. However, the piston was turned from aluminium, cross drilled for the gudgeon pin (or wrist pin as it is called across the pond). The con rod was turned up on the lathe and again transferred to the mill for putting the flats on both small and big ends. The con rod needs to be turned as narrow as reasonable to clear the base of the cylinder.

The crank shaft was machined from stainless rod to produce the flats which cleverly act as inlet and outlet ports. Clearly to be effective your crankshaft needs to be a very snug fit in the bearing to avoid air loss. I am sure it is not aproved engineering practice but as you will see from my picture the crankshaft was overhung from the vice for milling the flats. Very light cuts were taken and a satisfactory result achieved.

Care needs to be taken when drilling the exhaust outlet along the length of the crankshaft – slowly does it with plenty of backing off and cleaning and lubing of the fine drill bit. The crank was ‘loctited’ into position making sure it was set square to the inlet and outlet flats on the crankshaft – refer to your plan.

Now I would like to tell you that I assembled all the components, connected up the air and off she went. Well I found that I couldn’t quite get a full rotation due to the top of the piston making contact when approaching TDC. I used a milling cutter by hand to clean up and ‘bottom out’ the head of the cylinder. The engine now rotated by hand – a spot of oil added to cylinder bore and bearing surfaces, air connected and off she went and after just two or three minutes she was running a treat on around 5 p.s.i.

Elmers Standby