I've seen that when I did the original treat on this knife but I was using pretty direct heat (had the knife pretty much right at the end of the flame. Later I tested a piece of plain carbon steel and found that the heat required was way lower than this knife and decided that I over heated it. So, I normalized it a few times later and did the heat treat that I described earlier. As I said, we brought it up really slow and the whole blade came to heat gradually and I didn's see any shadow. What I found out though is that the 5160 has to get a lot hotter than plain carbon to reach non magnetic so the temperture that I went to on the first round was probably fine. I had just done it much faster and with more direct flame. I do think that I got a better hardening on the slow gradual heat up though. Gut thing. Nothing to back it up with.
I'm inclined to say that you don't need anywhere near that size if your chamber is well insulated (and of course not *too* large). I have to think it is desirable to keep the flame well away from the steel so long as you can get the temperature in the chamber up. This is what I have been working toward and for the most part accomplished. My only concern is that the flame on my naturally aspirated burner is still not mixing the fuel as well as it should. Still get a bit of the "yellow salamanders" dancing around in the chamber. Has a lot to do with stray currents from outside the chamber both at the intake and the exhaust/work opening. I am hoping that when I get the T Rex burner I will see a much improved performance.
Hmm. I'm using a needle valve myself. Cheap and gets the job done. I'll do the regulator later when I don't have more immediate concerns for where to spend my money.
When you say "exit pipes" are you referring to the mixing tube and burner nozzle? My buddy with the forced air unit ended up putting a ball of steel wool just behind the gas jet and got an improved mix out of his torch that way. Any obstruction in the mixing tube and forward will work as a flame holder if given a chance.
My buddy took a hex nut the size of the tube diameter and filed noches into the flat sides and then welded it into the end of his mixing tube. Works ok. Gets a bit hot if used for a while.
Now that sounds like fun. I'm thinking of making a set of steak knives for the family (without the stupid serrations). I'd like to do them in carbon steel with a hamon line just for kicks. I got my hands on some "plow steel" from the local Scrap & Steel yard. probably 1060 or 70ish. I'm making a custom camp hatchet for a friend and the scraps will provide enough material for several more knives.
Sounds like good all around material.
Got it on Sat. A hard bound school book. My favorite kind! Good shape too but the guy who owned it before me was neurotic about writing his name all over it. Not that I care. Lots of good information there. Should keep me busy for a while.
GA