Thanks very much for all the info. I do understand better, that was driving me crazy. I just use the file as a guide. The main things I go by are edge flex and cutting test. I usually cut 3/4" hemp rope. Those aren't all inclusive either, but the main thing I expect is the knife to cut and hold an edge. I also use the file test as a guide I have had a file bite into a blade I thought was hard a few times.
Thanks again guys
Reliable and accurate tests are geared to eliminate variables and test a very narrow group or a single specific property. The single largest pitfall in knifemaking these days is in the accurate interpretation of the results of any given tests, it is one thing to do a test, it is another to know what it is, or is not, telling you. Files and Rockwell testers both measure hardness but hardness come on a couple of forms, in fact hardness is more a concept we use to represent different types of “strength”. Rockwell measures deformation much like Brinell, Vickers and others ,the file is more along the line of the Mohs scale often used in minerals.
The edge “flex”, like any flex testing, is most accurately used to measure consistency in thickness and geometry, not so much heat treatment. There is a claim passed around modern knifemaking that it was a test used in old German cutlery facilities, while this is true what is left out of that tale is what part of the production it was testing. The guy responsible for the edge flex test stood behind the guy who was grinding the blades to insure his grind consistency.
I do use the file test often, but always in conjunction with Rockwell to get a more complete picture. And you touched on the time when the file yields very good information- when it easily bites into the steel. There is no mistaking that. If the file bites the steel, the steel is at best softer than the file. The only time this may be a false reading is if you test too soon after the quench and the blade is still in the process of hardening, but a follow up test a little later will reveal this.
I think it is a difference between “pass/ fail” type tests, such as the file and the edge flex, and tests that give us solid numbers on a scale, like Rockwell. The former can only tell us something if the blade fails, they don’t give us degrees of success by which we can even further improve our blades. Thus many folks are never aware of the untapped potential and gains they could make if they weren’t being told that it was “good enough” by limited or misleading testing.
P.S. BD Blade, and others who start other threads with good questions , I am sure you already realize these things, so don’t take my continued expansion of the topic as an indication that I feel the need to lecture you. But the reason we do this on a forum instead of with e-mail is for the benefit of all those who will come here and read these threads looking for answers to their questions. I constantly am contacted by people who have found things I wrote years ago and have new questions. Each of these threads is also for all of them as well.