Hardness Testing

Don’t get me wrong Fellhoelter, I am squarely in your corner here as I rely heavily on Rockwell hardness in my evaluation. But there are many who feel as long as they get a certain HRC number that they have all they need to know about the knife, and it is those folks I am trying to reach to let them know that only if you have all of your ducks a very tight, rigid, row can you rely on one test in such a way. I will take a good Rockwell number over just about any commonly used bladesmith “test” to evaluate blades, e.g. bending in a vice, flexing on brass rods, mincing rope for hours etc… which are all incredibly subjective and often don’t even measure the properties we are looking for. The Rockwell test on the other hand does very accurately measure penetrative hardness in ways no other test can, and produces very standardized and repeatable numbers.

But the numbers must be taken in context. I think the Rockwell tests works best for those who have a good handle on and control over the entire heat treating process, for then they can be more confident as to why they are getting the readings they are getting. If somebody is heat treating in a camp fire or with a torch and has no way whatsoever of gauging temperature, Rockwell will be of little more benefit than just whacking away at a hard object. For example, say you used a torch and overheat the steel, overheated steel actually hardens much more deeply so your HRC readings will tell you your heat treat is really great due the high hardness you are achieving, what it is not telling you is that you are getting that hardness because your grains are the size of golf balls. In this case Rockwell is misleading but a good chop, or even a flex over a metal rod, could reveal the serious flaw in that blade.

But if one has good control and consistency in their heat treatment, I entirely agree that accurate Rockwelll numbers are an invaluable tool, and one that I rely on every day. I know they are reliable because I verify them with other tests equally as reliable and scientifically accurate.
 
Fellhoelter said:
Let's go a slightly different route here.

I fear I'm coming off as an A$$.

What other testing should I be doing to verify my results out of HT?

I am a trust nothing, verify everything kind of guy.
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Fellholter,
Never think that entering into a conversation and debating the points brought up here or anywhere else is being an A$$! It's these kinds of conversations that help us all learn! With that said, I am not by any means saying that anyone should be rude, actually I think your posts were worded in a about the perfect manner, we can all agree to disagree if the need arises. But if we skim over oppourtunities to learn like this, we all suffer.

To the point you're making, you want to know for a fact that your blades are a certain Rc, that is understandable, I think Ed's point is, provided your equipment is predictable, that you can get predictable results using the same methods on the same steel, we all know the same type of steel differs from batch to batch and manufacurer to manufacturer (1084,1095, etc), and sometimes the process of Ht'ing a blade has to be tweaked. With that said, once you run your test on a new batch, most makers will make a blade for testing to destruction or close to destoyed. If after chopping (with a chopper) seasoned oak and I have chipping on the blade, I know the HT isn't right. In reality it may not take testing to destruction, just some extra work cleaning up the marks made by using it in basic tests. The other point Ed was making was that it's not ALL about the Rc, the Rc can be dead on, but if it'd too hard/soft for the grind, edge geometry, etc, the blades performance will suffer, Ed's point is that newbie's that don't have the cash to spend on a RC tester really don't have to test every blade, that was his experience he was sharing, it's the sharing of these experiences that help us all learn and maybe not spend money where we don't have to. And it's your questioning how and why that also helps us learn, this is why new-makers today are getting better much faster than they did in the passed, that and better equipment they can build themselves, it all helps, just my 2 cents, Ed, I hope you don't mind me interjecting here. When noone is is being rude or inconsiderate and thinks they may be percieved as an a$$, my fear is that more folks will be afraid to interject their questions or concerns about something the we can all learn from. I think this is the main reason this forum has exploded the way it has, the reason folks feel comfortable to speak up, and not be scorned for asking a "dumb" question, <do know the only dumb question is the one you didn't ask!> Had to throw in that disclaimer, Rex

BTW this is a great thread, I've wanted a RC tester for a while, and have looked at many of them, I just never got lucky looking on fleabay, or Craigs list or anywhere else, plus I've been quite satisfied with my blades performance so far. Knowing that mistakes can be made and not known is why we give our customers warranties, if it makes you more comfortable to do the Rc testing and helps you feel like your blades are better because of that, by all means -do it! That doesn't mean that others that don't (i.e. can't) test their blades are of lesser quality, they have to learn how to make blades that satisfy themselves first, then worry about customers once they get all the other aspect of knife making figured out as well! This is only one part of knife making, the main point here was that the Rc number is only one part of the equation, once you factor in all the other aspects of the blade, and I believe, after some real world testing will you know if you've got it dialed in, again this is my opinion from my experiences. That said, if I could get a Rc tester tomorrow I would, because it is another tool to help me make my blades better. Thanks, Rex
Is this color better?
 
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The blue font is very difficult to read Rex.

I think that Brian and myself as well as a lot of other guys here like to use stainless steels such as CPM S35VN and that they do require precision heat treating. You need to use a kiln, not a torch or forge. The Rockwell test really lets me know if I got the result I am looking for in a measurable way. It also let's me know that I am quenching the blade correctly. I like numbers and I like things to be precise. There is not another test which can give me info on my heat treat like the Rockwell test that I am aware of.
-John
 
Kevin R. Cashen said:
...very standardized and repeatable numbers... must be taken in context.
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At the risk of over-editing, I suspect that's true of testing in general.

I really have very little to go on other than my faith in my HT guy and his ability to take accurate Rc readings; so for now I try to back them up with "real world" tests like hacking through 2x4's and such. I'm not really satisfied with that but until I learn more and get better equipment, there I am.

Rex... seriously bro, John's right, the italic blue font really isn't a good idea. The way my screen is set up I can barely read it :( I'll add that the enter key is your friend... breaking up a post makes it much easier on the eyes than a big wall of text.
 
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Sorry guys, I fixed it, I'm at work and was in a hurry, the blue didn't look bad or was hard to read from here, I guess if you know what it's supposed to say it's not the same as reading it the first time, I changed it to black, and James I'll try to break up the posts some, I usually try to do that some without making it look like it was broken up for no reason, it doesn't help that I take so many words to make my point either!
 
Glad at least some of you thought I wasn't coming off poorly.

Being a Toolmaker for years, it goes against my nature to "trust" an operation like Heat Treating without testing it.

Especially since the OP is new to the game, and talking about buying a new oven.

Until some things are verified, there's just no way to know if all is well and if the oven is even working properly.

I don't test every blade, but I do test every batch.

Before tempering, and after.
 
I think that a lot of us would like to be able to do more testing than we can do. Not being able to afford the instruments needed or being able to hire the testing to be done for what is just a hobby all that is left for us is use based testing like seeing how a blade cuts and to do the occasional distructive testing to be sure that the knife performs well.

Doug Lester
 
Just my two cents...

If you had a tester in your possesion, I believe you would religiously use it after every HT episode. I bought my oven and tester near the same time and the difference it has made is bar none. The tester gives you so much opportunity to experiment and verify everything you do.

HT'ing is a very touchy concept/practice. Since I got my oven, there have been two-three instances that I have HT'ed a blade and came out with inferior results (either after the quench or the temper). Without the tester, I would have never recognized it. The only thing that sucks about the tester is that you really can't get the whole truth about the edge, but if you test the tang (as close to front that is hidden), you still get a good idea what is going on after quench and temper.

There was an instance that I found out that my temper (typical recipe) came out too soft. I caught it with the tester and re-HT'ed it. There was also another time when everything felt as usual but I found that I didn't get full hardness out of the quench, so I re-HT'ed it. It just seems like things don't come out perfect when everything feels like it is going as usual. That is where the tester comes into play.

To say that a tester will answer all your questions and problems, that isn't true. It can, though, give you a good control for your experimenting and verification. There is no way that a tester can tell you the best hardness for a steel or knife, but it can verify that your HT recipe is too hard for this steel or application or too soft for another.

If you can afford it or find a way of using one for HT'ing purposes, I think you will be glad you did. I also think you will find you will test more, both with the tester and physically. I have found that using it has led to me saying "what the he'll went wrong, I did everything exactly as before!" I think you'll find that HT'ing isn't as predictable as thought, at least for less experienced guys. Or maybe the tester is wrong:)! LOL
 
I need to learn how to write better. You expressed what I was trying to say much better than I did.
 
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Buy a a hardness tester as soon as you can afford one- maybe even sooner. I bumbled around for about a year making knvies from 1095, and they all were soft. Then I got a hardness tester from Enco, and everything came to time! You can only trust blind luck so far! And, it is not very rewarding to replace knives.

If you have any welding equipment and knowledge or know someone who does, you build a gas HT oven very cheaply. That was a fun project!

Milt
 
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