Making Replacement Parts - With a Lathe
I have a modest hobbyist-level metalworking shop in my basement: a drill press, bandsaw, and metal-turning lathe. These are all bench-top machines, not stand-alone, and they all run on conventional 115V AC, less than 15A. People say that "the lathe is the machine that can reproduce itself", because it has a motorized spindle and a platform that can be precisely moved on two axes. With a modest accessory, you can acquire three axes of motion. Lathe work often involves clamping something big and round in the spindle, and spinning it around while a cutting tool is clamped to the platform in such a way that it cuts into the spinning material. Think axles, spokes, bowls, candlesticks, etc. You can also clamp a cutting tool into the spindle, and clamp a piece of material onto the platform, so as the platform moves, the cutting tool removes material along a path. Think "boring out a combustion chamber for an internal combustion engine", or "cutting a slot in a sheet of metal". Between the two operations, if you have a way to cast chunks of metal to the approximate shape you want, the lathe (within the dimensions of its motion) can reshape things quite precisely.
My most recent project seems modest: I bought an old measuring instrument (a "vernier height gauge" to be precise) which requires three thumbscrews for proper operation. Mine had two. So, I used one that I had as a model, and machined the third that I needed (and one more, as a spare). If you've walked through the fastener section of a hardware store, you might think that every possible screw in the world can be had for a few cents, but I couldn't find ANYONE who could sell me a #4 screw, with 48 threads per inch, 3/4" long, with a 1/2" diameter head. Of course, it had to be 4-48, or it wouldn't fit into the instrument. It could have been longer than 3/4", but I couldn't find longer. And it could have had a smaller head, but then it would have been harder to adjust. But, in the end, I made the screw I needed, learned some new skills in the process, and turned a $20 bench decoration into a layout tool for future projects that would have cost hundreds of dollars to buy.
If you happen to need a special screw, or some other special nugget that does something "infinitely improbable", let me know. We'll talk.
Admin Note: Moved to "Green Wizard Book of Skills" 3/29/19