MY CORLISS

ENGINE BUILD

Part 15  by Vince Cutajar

I managed to find some 16mm square section 316 stainless (I would have preferred 303 but beggars can’t be choosers) for the connecting rod. Cut a piece of the 316 stainless and cleaned up the ends on the milling machine. I made it 12.7mm longer than the plans but that will be removed at a later stage.

As I intend to work between centres, I centre drilled both ends.

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I used the 4 jaw chuck to hold the material.  As can be seen the X3 table is getting a bit crowded.  I did some marking for the two holes.

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The holes were next drilled and reamed 6mm.

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I first machined the flat ends on the connecting rod to size and then transferred the part to the lathe between centres. It is a bit of an ‘iffy’ arrangement but it has worked before for me.

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I turned the middle part of the connecting rod to 9mm diameter.

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Next was profiling the middle part. I had already decided that a fishbelly profile was not for me (I hate fish and live on an island!). So the next best was a straight taper. Went on the internet to find a right-angle calculator (hopeless at trigonometry) and  calculated that the angle should be around 2 degrees. Set it up and made a dry run to see if it was correct and decided that a little more taper would look better so increased the angle to about 2.5 degrees.

Using a round profiling tool, the first middle of the taper was cut.

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Flipped the part around and the other taper was machined.  And the two tapers finished after a little polishing.

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I decided next to finish off the crankpin side of the connecting rod. It shouldn't take long. Or so I thought.

So I marked the excess material I had. Cut it off and milled it to clean it up. I brought out the crank to see how it all fits together.

The crankpin wouldn't go in the hole. The crankpin was 6.5mm and the hole 6mm. Opened up the 6mm hole with a 6.5mm slot drill to give me a smooth finish. Still a tight fit. How I wish I had used a 6.5mm twist drill instead.

A long time was used up to polish the hole and the crankpin until the pin fitted smoothly in the hole. Then I noticed that the head of the crankpin was a little large. It was 13mm diameter when I needed it to be 12.7mm. Eventually this was brought down to size in the lathe.

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A little more progress on the connecting rod.

The 0.25" excess material on the crosshead side was milled off.

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Work on machining the fork was next. Drilled and milled the excess material out.

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And then l used a slitting saw to remove the radius the end mill left on the inside of the fork.

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A little filing ensued to get the crosshead to fit nicely in the fork.  Next operation was to round off the end of the fork on the rotary table. Made a sacrificial aluminium bush to fit tightly in the fork,

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and the rounding-off operation finished on the rotary table.

Next, and final operation on the rod, is to give the sides of the fork the tapered shape.


Drawings here

Part 14 here Part 16 here

 
https://www.sarikhobbies.com/model-engineer-builder/

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