Hardness Testing

Chall

Well-Known Member
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?
 
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.
 
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,
Rob
 
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?
 
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.
 
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!
-John
 
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....
 
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.
 
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...
 
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.
 
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.
 
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.
 
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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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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