Wednesday, February 29, 2012

First experiences with the lathe

Some months ago I set out to fabricate a miniature steam engine, following the plans in Tubal Caine's 1981 book "Building Simple Model Steam Engines."

It's a real challenge to bring oneself up to speed on a project of this nature. At the outset I possessed exactly none of the required tools or raw materials, and little of the know-how. Thank goodness I found TechShop just a few miles down the road.

I decided to begin by machining the flywheel. I figured this would be good practice for the finer lathe work required for the piston, and in any case I would need to cut the "formers" for the boiler out of the same stock. With the introductory metal lathe course fresh in my mind, I innocently ordered a footlong bar of 2" diameter cold rolled steel from Amazon.com.

The initial cuts went well enough. The real problem was parting it off at the end. I spent over an hour trying to cut through the darn thing on the lathe before I ran out of time on the machine.

Of course I had cut the piece too short to mount safely in the big bandsaw. A TechShop technician suggested the "chop saw," where the next phase of the ordeal began.


This also took a couple of hours, right up until closing time. Progress slowed when the piece heated up and I had to pause frequently to let it cool. Towards the end I picked it up with a pair of pliers and dropped it into a coffee can full of water, which was immediately brought to a boil. I had no idea that so much energy could be held in a few cubic inches of steel.

The flywheel finally came off. Here you can see the marks made by the saw, as well as the oxidation following its bath.




I went back and surfaced the back side on the lathe, and I found the end result to be "good enough." Ironically, the side that I had so much trouble cutting is smooth and shiny after being faced off, but the more complicated bevel shown above is now rusted from the water in addition to horribly gouged by my amateurish lathe work. I might make a fresh attempt later, but more likely this first piece will set the tone of the entire project.

I am vaguely aware that I ran afoul of the "work hardening" phenomena, and perhaps quenching that steel in water had some side effects that I didn't consider at the time. My main takeaway from this phase of the project is that I need to learn more about metallurgy in order to be an effective machinist.

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