is it that you like the edge to have all the grain refinement ? why not make the whole blade just as refined? is there a benefit to having a spine thats not as refined as the edge ?
if you still wanted just a hard edge you could always just edge quench
i love the kiln for repeatability while im not questioning your heat color eye witha torch (ok maybe a little ) why not have a +/- of under 2 % and know for sure what your temp was (yes i know kilns can go bad too)
Evenheat kiln will have some variation in temperature (one zone and a temp probe at the top). You can figure what the likely temp of your piece is by some experimenting heat treating and measuring hardness, but you still might be off by 10-25 degrees at low temps and more at high.
Sugar Creek kiln is better this way, as a probe is on the side, just above the floor level, but it has two rows of coil instead of 4 of Evenheat (it will heat up more slowly), and at $200 less, it might not be a better deal over Evenheat.
In that sense, you don't get precise temperature measurement, unless you add additional sensors into the kiln or able to measure temp of heated piece with an infrared thermometer (industrial grade - very expensive, all others - inaccurate). To know at what temp you heat treat and temper, you have to do a bit of experimenting, testing for hardness and recording your findings. There will be some guess involved at all times.
Which is to say that it will be not that different in terms of accuracy than torch heat treating. Heat treating with torch (by eye) could be pretty accurate, as long as your eyes are not failing you and you test your work for hardness and cutting ability regularly, as I believe Bill does.
also good to have a baffle for at least the sides of the blade to keep the heat even and not being directly "blasted" buy the coils when they cycle
the added mass also helps keep the temps for swinging wildly
and for the guys that temper in there home oven or toaster oven a brick or 2 will help leaps and bounds (keep the blade between the heated bricks )
What do you use for a baffle, Butch? I got two extra bricks with Sugar Creek, wonder if this is what they are for.
Roman Landes swears that W2 can and should be left harder than "normal" even for field knives. I think he leaves his at around 62RC.
My kiln was made by evenheat, but it is not a traditional knifemakers kiln. Mine is vertical 36 inches high and has 16 rows of coils. My controller(Omega) and thermocouple was not included and I put that system together myself. They are located in the middle of the kiln right where the blades go. I have tested my system with yet another thermometer and my system has an accuracy of 2 degrees even in the 1500f range.
I believe in constant testing and even test-to-destruction and I do that to insure quality control.
I strongly believe that making a blanket statement about the accuracy of all kilns over other methods of heating is inaccurate and misleading.
What I do find misleading is when people state particular hardness on a finished knife without using a hardness tester. I accept that experience will help one to establish a range, but not an actual number.
In my previous life my boss showed me his Puma pocket knife one day and you could see the Rockwell indentation on the knife and they scribed the number right next to it. Very impressive to me. I've never seen that on any other knife. He told me it was an old knife and even Puma had stopped doing it. Shame, I thought it was pretty classy.
I still have problems with Rockwell reporting. I remember my standards were +/- 0.5 at best, example 50 HRc +/- 0.5 would be scribed on the side and the dial had 5 unit increments if I remember correctly, 90, 95, 100... etc. The machine didn't have the resolution to differentiate between 60 and 62 nor the tolerance to do so either. This was on my old Wilson unit. Maybe those fancy digital ones are a whole 'nother ball of wax.