Hardness tester - use and accuracy on forged blades?

Eddie Mullins

Well-Known Member
I am considering buying a hardness tester at some point, but as I primarily forge blades, I am wondering if it is even a worthwhile investment. From what I can understand, the reading is only accurate on flat surfaces. As I will forge in the initial bevel, I am wondering if I could even test the edge hardness?

I see some descriptions that say cylindrical and irregular shapes can be tested.

http://www.use-enco.com/CGI/INPDFF?PMPAGE=403&PMITEM=505-1897

Is this accurate? can it be done on a bevel?

I am also wondering if this is even useful information, unless its tied to performance testing. And if I am going to performance test, why do I need the Rockwell number, unless its simply a selling point for some customers?

Sorry for rambling. I'm sure this has been hashed out before, but I couldn't locate information on testing forged blades and am curious about your thoughts on the merits of hardness testing in general.
 
Yep, that's the same most of us use. You might try Grizzly.com for a cheaper price.

http://grizzly.com/products/Hardness-Tester/G9645

Thanks, I have looked at them also, but my question isn't so much about which tester to buy, but are hardness tests accurate for forged bevels since they are not flat?

For those who are looking to buy, Enco has 25% off and free shipping sales occasionally, they had one yesterday, so to your door it would be about $100 cheaper than Grizzly.
 
Nope, I think the idea of testing on the bevel after it's ground isn't a good thing. Testing of hardness MUCH have a totally flat surface on both sides.

Yea, and I purchased the Grizzly tester back when they were a tad over $1K shipped.
 
I'm certainly no expert when it comes to hardness testers, but those that I have had experience with REQUIRED the test piece to be FLAT. Personally I have never heard of a hardness tester that would give an accurate reading on something like the bevel of a knife blade.
 
I'm certainly no expert when it comes to hardness testers, but those that I have had experience with REQUIRED the test piece to be FLAT. Personally I have never heard of a hardness tester that would give an accurate reading on something like the bevel of a knife blade.

That seems to be the consensus from all sources. So unless I am missing something, this basically renders the test useless on a forged blade.

What then should a blade smith do for evaluating their blade? performance/cutting tests? hardness test files?
 
Eddie, it has to be mounted flat. You can get an adjustable angle block, or a sin plate or make a tapered shim to hold it flat.

John
 
I was going to try a way to say this in my previous post, but since you asked..... :) In many ways I despise hardness testers, and more so those who put WAY too much emphasis on their use/results. Don't get me wrong, a hardness tester has its place, but in the overall scheme of making knives, that place is only a small part of a much larger equation. Yes, knowing what procedures (heat treat or otherwise) for a given steel, will give you a specific Rc value is a key piece of information, but it's certainly not the "know all, end all" that some believe or advertise it to be.

I was hung up on the same thing early in my career..... thinking that harder is better. Boy did I miss the boat! :) I spent about a year taking steel samples to a local community college, where I paid them $5 per sample to hardness test for me..... when I started to test my blades in a practical manner (cutting rope, chopping, edge flexing, etc) I quickly realized that I had placed far too my emphasis on a blade's hardness, and had not thought of other aspects such as toughness, ductility, ect. By that time the hardness testing results had become so predictable that I was wasting my time and money anyway. Long story short, I finally came to understand that making a knife is about what I term "The Overall Package".... its a combination of steel choice, blade geometry, edge geometry, methodology, overall configuration, and the heat treat to match/compliment all those other factors.

Personally, for someone in your position, I highly encourage practical testing. Cutting, chopping, edge flexing, and/or any other practical "test" that offers you feedback on how your blades perform. As for a "standard" that a forge blade should meet....that is totally up the the individual Bladesmith. It is also somewhat of a moving target in that as we progress, the standards for our blades tend to change. Even after all these years of doing it, I will still randomly take a blade and torture it to death, just to ensure that I am adhering to my own standards. At the current stage of my Bladesmithing career, I place very little emphasis on hardness testing, or the results from it, and more on the practical function of a blade.

A couple of things that might be helpful to you are:
Learning how to use the "brass rod" edge flex test: http://www.caffreyknives.net/testing_art.html I find this to be a very accurate test to determine the correct working hardness for a blade. If you have any questions, just let me know.

This is an article I wrote for my website about what I call "The Overall Package": http://www.caffreyknives.net/top_art.html

I also have a number of other articles that might be of interest: http://www.caffreyknives.net/articles.html as well as videos: http://www.caffreyknives.net/how_to_videos.html

Keep in mind that these are my personal views, and the methods are what I do. That doesn't mean they are the only way, but they are the way(s) I've discovered that work best for me. :)
 
Ed - Thanks for the reply, you took this where I was hoping you would. I agree that performance is the ultimate goal. I think hardness testing is simply an instant measure of one attribute, that makers and buyers can use as a point of comparison. There isn't a standard performance measure for comparison, at least that most buyers would acknowledge. I am coming to the opinion that for Bladesmiths Rockwell hardness is more a selling aid than anything, and often the values reported are not actual results, but expected (not tested at all or not done accurately).

I have used 1/4 mild rod for edge flex testing and have done 2x4 chops, no hemp rope cutting yet. For my wood carving knives, I ..... carve wood : ) . I do want to develop some sort of standard performance test, whatever that might be, so I can compare and confirm the performance of different knives or steels etc.

Thanks for posting the links, I have read most if not all of the info on your site before, but it has been a while. Its probably time for a refresher. Great info, thanks for sharing it!

Since we have gone down this path, I think Ed Fowler has some excellent advice out there on performance testing. I could buy a lot of rope for cutting tests for the cost of a hardness tester : ) .
 
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