Hey, folks: I'm thinking about making my own A-2 irons for my infill hand planes, and I have a few questions.
1. I've read varying accounts on heat-treating A-2 tool steel as distinct from O-1. All say you must plunge O-1 into oil after soaking it at the proper temperature, but when it comes to heat-treating A-2, some say plunge it into oil and some say let it cool in air. Which is correct?
2. Accounts vary as regards tempering the steel, too. Most say you must temper the steel directly after heat-treating it, but I've also read that you can re-temper steel. If you can re-temper it, what's the rush to temper it in the first place?
3. Last but not least, why heat-treat the entire iron? Put another way, why not heat-treat only the business end? I've done some experimenting with a torch and a make-shift chamber formed out of fire brick, and I've had no trouble getting the business end of several test irons to the point where the color "blooms," or suddenly changes from red to bright orange. The chamber was narrow, making it impossible to treat the entire length of the iron - which would be hard to do in any case with a torch. But the irons sharpened up nicely after plunging them in oil and then tempering them in a reliable oven, and it occurred to me that I might not need to worry about heat-treating the entire thing. Am I wrong?