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Lerch
07-27-2011, 08:02 AM
After laying awake last night unable to sleep this though came into my head, how crucial is the contact of the aluminum plates directly to the steel (or steel foil) to the conduction of heat from the steel?

All of my knives so far have been hollow grinds on either 1/8" or 5/32" stainless and on the 5/32" there is a decent gap when the plates are sat down on the handle and backbone of the knife and the actual cutting surface. I am thinking that this would cause the spine and handle of the knife to be harder than the cutting surface, and i would have thought you would have wanted the exact opposite to be true

if i was to know which side of my steel foil the cutting edge was on could i place blow air across that side with the foil on and harden the cutting edge more properly? or am i thinking stupid from the beginning here and this is no issue at all??

thanks
steve

Knifemaker.ca
07-27-2011, 10:02 PM
Nice to know someone else shares my nightmares. :13:

I had the same thought, so I did a test. I took a bar of 3/16 (154CM if I recall) and ground it flat at 3/16 - another flat at just over 1/8 and the last flat at just under 3/32. I then hardened it - plate quenched it and cryoed overnight. Without tempering, I tested it in several places on each flat. The readings were all the same +/- .5 RHC.

Obviously the two thinner flats never contacted the plates, but the RHC was the same. Plates suck the heat out of the whole bar lots faster than air quenching would have - plenty fast enough for full and effective quench. As an example, you have something like 6 minutes to get 440C under the nose (about 1200F) - and it's long past hand cool long before that.

Rob!

Lerch
07-28-2011, 08:39 AM
thanks for the info, glad to know my concerns werent groundless, even more glad to hear it isnt a problem :)