View Full Version : Hardness Testing

03-24-2011, 08:02 AM
Thinking about taking the plunge and buying a heat treat oven. My question is how to test for hardness without buying an expensive tester. I see the formulas for heat treating cycles and tempering times but how do you test the hardness?

03-24-2011, 08:47 AM
To really know, you gotta have a tester.

Look for the Aames handheld testers, it's harder to find a deal on them now that knifemakers have discovered them, but not unheard of...

Rebound testers suck for thin items like knives, and files only ballpark it for you.

If you want to actually KNOW what hardness you have, you have to test.

03-24-2011, 08:59 AM
Sending the blade out to be tested is one option.

Although very crude and general in nature, another option would be using hardness testing files. But that merely gives a "ballpark estimate" at best.
Still, it is an economical means to check your methods when new to heat treating. I don't believe I would use it to compare methods, or even to compare different steels. Simply to know if the steel is "harder than this, but softer than that".

My impression about hardness testing is that it is destructive in nature. Meaning that "cleanup" is required, and you're left wondering if you have the same hardness throughout. Also, location of testing comes into play. I don't understand testing the tang when the true question concerns the blade, so the methods employed during heat treat are also considerations.

I have yet to have any of mine tested, but then again, making knives is something I do for my own purposes, not for intent of selling to others.
If the time comes when I do need to know, my machinist down the street can do it for a couple of beers.

For now, I do as I've always done- try the blade out under real-world conditions and see if I'm satisfied with it.

Someone like Kevin or anybody with more experience in this subject needs to provide you with more guidance, because I know just enough to get into trouble!:biggrin:

It is my understanding that this subject is a science unto itself!

Good Luck,

James Terrio
03-24-2011, 09:05 AM
If the time comes when I do need to know, my machinist down the street can do it for a couple of beers.

Brad at Peters' HT Rc tests my blades now after he heat-treats them, but when I start doing some of my own I will call around for a friendly machinist with a tester. Couldn't hurt to ask, right?

03-24-2011, 09:48 AM
Thanks guys. As always, the information I get on the forum is great.

03-24-2011, 09:59 AM
Brad at Peters' HT Rc tests my blades now after he heat-treats them, but when I start doing some of my own I will call around for a friendly machinist with a tester. Couldn't hurt to ask, right?

You're absolutely correct; it never hurts to ask around.
Thing about it is- there's machinists, and then there's machinists. Not all has one, and just because someone has one does not necessarily mean they know what they're doing, at least as far as our objectives are concerned.
A lot of it depends on the specific type of shop they run. A tool and die maker may get you somewhere, whereas the automotive shop turning your crankshaft may net you a dead end.
Never hurts to ask around. Many times they can at least provide leads elsewhere.

John Barker
03-24-2011, 10:30 AM
I have an Aames tester. It was new in the box with all the goodies and the certification was up to date. Got it for around $300 on fleabay, which was a steal!

James Terrio
03-24-2011, 10:57 AM
A tool and die maker may get you somewhere, whereas the automotive shop turning your crankshaft may net you a dead end.
That's exactly what I was thinking. It also occurs to me that I could ask at the local tech college, they have a pretty extensive machining program which I'm still thinking about weaseling my way into anyhow....

03-24-2011, 04:33 PM
For a while I paid the local college $5 per blade to have them tested.....after a while things became so predictable that I realized I was just wasting money. I also realized that getting fixated on a specific Rc hardness is not the key...I personally think it's much better to concentrate on achieving the proper "working hardness" for each given blade. That's not just a given Rc.....it's the correct Rc for a given steel, with a given grind, and a given edge geometry.

That being said, learning/knowing the specific Rc hardness lays the ground work for the rest of it.

03-24-2011, 04:42 PM
I personally think it's much better to concentrate on achieving the proper "working hardness" for each given blade. That's not just a given Rc.....it's the correct Rc for a given steel, with a given grind, and a given edge geometry.And without testing, you'll never know if you hit it or not...

03-24-2011, 06:28 PM
I have a hardness tester that seems to work ok with a 25 RC test sample but does not seem to read properly at higher values. I am looking for a 60 RC calibration test piece that I can afford.

03-24-2011, 07:00 PM
Standards are $32 at Enco.

03-24-2011, 08:38 PM
And without testing, you'll never know if you hit it or not...
Sure you can....if it's ONLY a specific Rc number you're trying to achieve, then you're missing the point of seeking the proper working hardness for a given blade.

03-24-2011, 08:53 PM
I must be missing something...

Each steel and geometry will have a best specific heat treat for the task the knife is designed for, which is what I believe you are saying.
I agree.

Which in my mind, and in my shop, means I'm looking for a specific working hardness when I run through a cycle.

The # will be different from knife to knife, but still specific to the knife going in the heat.

I think you need to test your steels hardness to know if you got the HT where you wanted it.

Especially the original poster.
He's just going to be learning how to HT, and without some reference measurements, he'll never even know if the oven is hitting the specified temps.

I believe these 22 folder blades out of CPMS35VN will perform best at 59-60Rc, so I heat treat to that formula, and verify with an Rc test to make sure my cycles did what I expected them to do.
Without verification, all is just a guess.

Experience goes a long way, and I always hit my desired #'s, but I still verify each batch or else I don't honestly know for sure that nothing went wrong.

90% of the time I am using my tester, it is mere to be assured that everything went according to plan.

Kevin R. Cashen
03-25-2011, 07:37 AM
Hello from the Badger show in balmy Janesville WI, Rockwell is indeed just one small piece of the whole picture but it is a very precise and accurate measure of that specific property, it can't tell you much about other very valuable properties or qualities in the blade, but neither can other tests not made specifically for hardness accurately tell you about the penetrative hardness. I see both sides, Many people believe that a good knife resides in simply achieving a certain Rockwell number, while others feel HRC values can be irrelevant, reality is somewhere in the middle. I personally do more Rockwell testing than most would, but it is just one methods of analysis I work with. One tip I would share is to beware of cheap test blocks, your tester is only as good as your test block, so if you have a $5,000 tester and $20 Chinese test block, the guy with a cheap Chinese tester but top of the line certified test blocks ($75-$80) is going to beat you in reliable readings. I would get cheap blocks for regular calibrating, an really good ones for occasional checking to see if all is still good.

03-25-2011, 09:04 AM
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.

Ernie Swanson
03-27-2011, 06:16 PM
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.

How well your blade holds up to the main purpose of the blade is, blade geometry, edge retention, and ease of sharpen.
From my understanding one knife made out of say O-1 could be better with a couple point lower or higher RC than another blade made of the same material.

03-27-2011, 09:37 PM
Absolutely true.

Now how do you KNOW when you hit that, without testing, is what I'm looking for.

Or, what different test is there?

Sure, we can take the knife out, and put it through it's paces, but I want to sell knives.
I can't go beating them all up...

We have to have a reliable test, out of the ovens, to know we got the HT we were looking for.

Rockwell testing is the only non destructive test I know of that I can readily do in my shop.

When my customer asks me I can honestly answer, because I tested.

03-28-2011, 04:35 PM
i think what the guys are trying to say i may be wrong but maybe he should work out what the entended purpose/ working geometry for given edge/ and hardness should be by testing his first 1 before setting anything in stone once worked out i see your point of rc testing a batch to see that it went well , but then again im sure you have worked out alot of that allready . just how im taking all of this.

03-28-2011, 05:31 PM
Ok guys I just bought an Aames hardness tester today off of ebay! So get ready! I will have lots of questions once I get it on how to use right.

Kevin R. Cashen
03-29-2011, 09:40 AM
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.

McClellan Made Blades
03-29-2011, 10:25 AM
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.

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?

John Barker
03-29-2011, 12:03 PM
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.

James Terrio
03-29-2011, 01:01 PM
...very standardized and repeatable numbers... must be taken in context.
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.

McClellan Made Blades
03-29-2011, 02:21 PM
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!

James Terrio
03-30-2011, 10:03 AM
Thanks bud, that's much easier to read now :)

03-30-2011, 10:09 AM
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.

Doug Lester
03-30-2011, 11:36 AM
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

03-30-2011, 07:21 PM
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

03-30-2011, 07:55 PM
I need to learn how to write better. You expressed what I was trying to say much better than I did.

03-30-2011, 08:06 PM
I thought I was feeling you the whole time, just didn't know what the confussion was!

03-30-2011, 08:10 PM

04-10-2011, 07:19 AM
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!