Well I should be on the home straight now.
Today I have produced the flywheel – a straightforward turning job on the lathe. Watch out for the thin 1/64″ bosses either side to prevent binding in the engine bearing or frame as I prefer to call it.
Next was the con rod for which I am showing one or two pictures – this was machined out of a length of round bar, drilled for little and big ends then tapered in the lathe and finally tidied up with needle files.
The piston was turned out of a hard plastic – Delrin or something similar. It machines beautifully, turned at a low speed as a precaution against meltdown. A gudgeon pin, or wrist pin as they call it t’other side of the pond, was cut from a 1.5mm drill bit using a small rotary diamond blade in my mini drill.
The final bit of machining was to make a forward and reverse valve as per plan – a delicate bit of milling with a 1.5mm slot drill. Everything was assembled with a touch of oil on each of the bearing surfaces and connected up to the air supply. I would like to say at this stage that it burst into life. It didn’t, I had had enough for one day so scrubbed up with Swarfega and grabbed a beer from the ‘fridge.
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- The diameter for the crank was turned to size in the lathe then zeroed with the aid of a centre finder.
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- After the first cut the ‘x’ and ‘y’ reading were noted so I could repeat for the other side.
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- Cutting the second side repeating the positional data from the first side.
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- Lineing up for drilling hole for 2.5mm grub screw on the flywheel
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- Machining flats on the conrod so it would still hold in the three jaw for tapering.
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- Drilling for ‘big end’ and ‘gudgeon pin’. The DRO propvides the required dimension accurate to 1/1000″ .
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- Angling the cross slide enables the centre section of the con rod to be tapered.
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- Machining valve for forward and reverse porting using a 1.5mm slot drill.
