I did geometry and trigonometry for 2 weeks, culminating in publishing a series of tables on the "Shop-Made Tooling" forum. I filled more than 10 sheets of paper with diagrams and formulae, and created several spreadsheets. I finally came up with some firm decisions for my train. And that means after many years of planning, building my shop (check the "Our Shops..." forum), and getting familiar with the tools on small projects, I have begun construction on my spring detent chronometer pocketwatch. Every journey begins with a single step. This is step one (of a million): This chunk of steel is going to be a specialized tool. I don't own a lot of expensive equipment, so even this simple cut will take some hand work. Get the hacksaw and cutting oil and get to work: Some rough grinding to put a 5 degree cant on the front edge, and drill a through hole also tilted 5 degrees. It is now a cutter base. The angle makes the tool insert hang out over the edge, giving relief to the insert as it cuts. The insert, which becomes the second tool I've made for my watch, has 5 machining steps. The radius of the top end is to within 0.01mm. It drops into the base, the relieved tip can now etch a radius of exactly 0.59 mm. The radius it cuts will be the inside curve of a second cutter. That cutter will cut the teeth of the center wheel of my watch. That's right, this is a wheel cutter-cutter. It makes a wheel cutter, which makes a wheel. Every wheel has its own cutter-cutter and cutter! Still a little work to do. I trimmed the shoulder from my cutter insert so it could sit flat on the stage of the cutter base. It is critical that the insert not move during the cutting process--the tolerances here are pretty damn tiny--so it must sit nice and tight. Also, I should clean up the base to guarantee it is flat, for that all-important support. Here the milling vice is mounted on the tilting table set at 5 degrees: Polish the insert, then off to the high-tech hardening station. If you look carefully, you'll see the tiny insert wrapped in iron wire ready to be dipped into the bowl of icy cold New Hampshire water. Wrapping it assures control as the red-hot piece goes into the water--it must enter vertically so as to not distort the dimensions. The hardened insert must be polished before tempering. I use a piece of hard, dry ash wood from a tree that grew outside my shop, sharpened and charged with polish. Into the bed of brass chips, which I collected last time I had to part a piece from a 1" brass rod (the largest diameter I've ever turned). The handy steel vessel was made by hand by my son! You may have laughed when I called the hardening station high-tech. But when you see my tempering furnace, you will understand I wasn't being ironic. Yes, that's the woodstove that heats our house. Since there's a fire going from November to April, and since I'm cheap as hell, I'm going to try to temper in there even though I've never tempered steel in my life. Oh well, what could possibly go wrong? I rake out some coals and place the brass-filled steel dish on them. Then I watch. I was looking to bring it to straw, but I figured I'd take anything short of dark blue. When it looked to be darkening, I grabbed the vessel with a regular leather glove and quickly put it onto the stone hearth to cool (and quickly removed the glove). Took all of 3 minutes. Let's be generous and call it dark straw, good enough! Finally, the tip is polished off with 2000 grit sandpaper (the base piece itself is the polishing jig), so it is razor sharp. Here's the tool completed and mounted in the toolholder of my lathe (note the straw-ish color of the insert): Next step, make a wheel cutter!