I need a bit of help heat treating my O1 molding plane blades. I have a setup of just a Bernzomatic 8250 torch with a can of Mapp gas and a few blocks of fire brick to hold in some heat. I'm sure I;m able to get the heat high enough with this setup but due to the lack of control I am not able to get a sufficient soak time at the right temperature. I've heard that this should be fine with such small blades in a molding plane (#8 Hollow and Round--1/2" radius). I've made my planes per Larry Williams DVD, which is great.
Anyways, my question is about knowing when I'm at the right temp. Larry suggests not using the color of the steel but watching for bubbles (which he calls flux bubbles) coming to the surface of the steel. I personally never saw any of these bubbles on my first and only attempt but didn't dare go any further as the steel color was into the orange range. I also had a magnet nearby but couldn't get that setup so the magnet wouldn't stick to my red hot blade, just got too awkward. What are these bubbles Larry is talking about and is it something truely reliable in determining the proper temp?
My blade does seem a bit soft so I'm not sure I really did get up to temp. But seems to hold an edge well enough to make the plane useable. In fact I'm very happy with the plane so far. But I want a better result on the matching hollow.
Also, I'm stuck on the tempering side of things as well. I have a reliable oven that I use but am not confident on the time and temp to temper the blade at. Larry suggests 375 deg and Ron Hock 325deg. But the time is not clear to me. Ron says 325 for 20mins per inch of cross section. With my half inch by 1/8" blade what does that equal? Might be a dumb question by I just can't wrap my head around that.
Last question is about re-hardening 01. So if Im not happy with the hardness of the blade is it possible to re-harden it? I've seen where it has to be annealed first before this is possible and that seems like it would be beyond what I can do with my setup. And I've also heard where there may possibly not be enough carbon left to re harden this blade.
Sorry for being so long winded. There is a lot more to this heat treating than I thought.