Hardness testing - there's GOTTA be a better way....

A

AndrewC

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Nov 14, 2017
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I'm a noob knifemaker, a bit over a year now, and have been baffled-to-irritated by the lack of reasonably affordable ways to test hardness, in the gap between $120 file sets and a $3k Rockwell penetrometer.

Ray Rogers has invented a rather ingenious penetrometer-type device that's clearly accurate - but it takes rather a lot of time and welding etc. After some reading up, I'm pretty sure the WWII-era sclerometer - aka 'how high does a ball bearing bounce off it compared to known samples?' - approach has a lot of merit. Hell, after buying just the 55 and 60 files, I'd probably be real happy with a set of those suckers if they were two HRC points apart and just in my range, instead of $120 for 6 files that go from 40 to 65. (Hmm....venture idea...anyone know how to make files...? >:)

There's always a clever hack. I don't need NIST-traceable results, just a good comfort level that I'm within a couple of points of what I need. If I can just compare my readings to a few reference blocks - which again, need not be blessed by Swiss elves in a seismically isolated cavern - I'm happy. Look: I make chef knives (including lately for some Michelin-listed folks), not collectors who're gonna take micrometers and loupes to 'em - I work the heat-treat (which I do, as well as vacuum-stabilize and everything else, myself) to the purpose and the customer preference, but everything I do is Japanese-style so fairly hard. I just need to know whether I'm hitting from say 57 to 63, depending, and where in that range.

(Given that the classic Mohs scale relies on just plain-ol' scratching, with a set of reference hardness substances, I'm curious as to why we need penetration as the standard method. I get it if you're differentially hardening or doing combo-metals, and don't like scratching your blades, but (a) I can test my tang and (b) I can test my blade before I do the final grind. What about just a set of "scratchers" - they don't have to be files, you could just sharpen 'em as needed and periodically verify on a set of known test blocks? It shouldn't be hard (sorry!) to crank out, HT, and test a whole bunch of pointy-sticks and blocks, right?)

Again - there's GOT to be a good hack that doesn't take a ton of money or time. Would love thoughts!
 
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Call the Local Machine Shops to find one with a Hardness tester and be polite and show up with a couple Burritos and ask if they can test your blades....Even if you have to pay a small amount to have a handful of blades tested you can begin a working relationship that over time may just cost a Burrito. I do this with a local steel supplier and bring extra burritos and walk away most time with what I was looking for at the cost of the food....OR Cough up the price of a NIST certified Hardness tester takes the guess work out of equation and you can state with confidence your blades are hardened to the proper RC hardness.
 
The rebound testers are very finicky. Ask me how I know lol. I bought a shore hardness tester that drops a diamond tiped plunger and catches it at the apex of the rebound. I quickly found out that on lower hardness ranges up to 50rc it is quite accurate but once you start going up past that it becomes unpredictable. It will give me corect reading but then a handful of miss readings. So unless you know what the hardness is how would you tell what the corect reading is. It is also very sensitive to surface finish. It is a cool device and looks great sitting on my book case where it should stay. You need a dependable RC tester. You can look around and find them used for a few hundred bucks but might need work. I scored a rams Rockford for like $100 and it’s super tiny. You could probably just about fit it in a glove box. It does not use weights but a spring as the weight. It’s adjustable so you can calibrate it. I have a 63RC gage block that I take 3 readings on befor I do any testing. It’s never needed adjusting once I calibrated it and left it in the 70° man cave. But temp can affect it, that’s why I leave it inside where the temp is regulated.
 
Larrin said:
There are threads here and there about the Grizzly hardness tester, which is between your $120 and $3k range: http://www.grizzly.com/products/Hardness-Tester/G9645
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Yeah, I've seen those threads (and the Grizzly) - but thanks! I should've been clearer about the "$ range" thing - that was meant more to illustrate the overall picture of what the options are. I still think $970 is too much - hell, my 2x72 grinder, plus motor, plus VFD was less than that - and it actually makes knives :-). All a penetrometer does is press a sharp thingy into something and measure the force and how far in it went. My $15 chinese dial indicator does .0001", super-accurate strain sensors are like $10. The $1,400 Ames handheld testers are basically a micrometer-like frame with a pressure gauge dial and a diamond point - if you didn't need them calibrated accuracy and the Chinese made 'em they'd be $79, free shipping, on eBay.

Sure, I could make 1.5 knives and that'd pay for the Grizzly, but that's not quite the point. If you're a beginning knifemaker you're gonna drop say $1,500-2k on a grinder, drill press, maybe one or two other power tools. Throwing an entire additional $1,000 to do a single test is just painfully disproportionate.

You can test sharpness, more or less, with some coated paper from a catalog you get in junk mail for free. You can measure down to a thou with digital calipers for $17. And note: there is (almost) NO such thing as a quantitative sharpness test!, other than something involving calibrated little rubber balls and I never see anyone using that. There's also no such thing as a quantitative toughness test, at least that people tout in their knife specs. And as to hardness, you can kind of know it from your heat-treating process, depending on steel and your temp accuracy (which is cheap to measure - IR guns are $16!): if I take 10xx to xyz° and quench past the nose and temper at abc°, I'm pretty sure I'll be near (ghi) on the HRC scale -- and that's been my experience.

Sorry but I'm on a rant about this today. Why can't I just buy/make a thingy that I bonk on my blade with for like $100 that tells me it's, yeah, about 60-62 HRC? (The more I type that, the more I'm thinkin' that it's called a set of files....just a different/tighter range.... Or something like this, just for steel: http://www.mineralab.com/MohsHardnessIndustrial/)
 
Hardness and hardness testing is way overplayed. Testing the edge with a file will tell you it hardened, Testing the blade with a brass rod test will tell you if the HT was good.
No home smith needs a hardness tester. A lot of full time professional knifemakers have one, but many don't. They are way down on the list of must haves in knifemaking.
 
If you think your calipers are repeatably accurate and precise to .001, your chinese mic to .0001, and your $16 IR thermometer for HT, this entire thread is pedantic because the file set is more than accurate and precise enough to meet your standards.
 
kuraki said:
If you think your calipers are repeatably accurate and precise to .001, your chinese mic to .0001, and your $16 IR thermometer for HT, this entire thread is pedantic because the file set is more than accurate and precise enough to meet your standards.
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Lol yeah my thoughts exzactly. My thoughts on this is if your making knives to sell or doing heat treating for customers then I OWE them the best most accurate results I can provide. I equate this to building a car and not being able to tell the person the HP or gas mileage or hell even the speed it will go.
 
JTknives said:
Lol yeah my thoughts exzactly. My thoughts on this is if your making knives to sell or doing heat treating for customers then I OWE them the best most accurate results I can provide. I equate this to building a car and not being able to tell the person the HP or gas mileage or hell even the speed it will go.
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Ummm.... there is a lot of custom auto work where the HP, gas mileage, and top speed are not known. Even from the factory you are discussing things that are estimates and averages. Maybe not the best analogy, or maybe it is. Like Stacy says above, hardness testing might be a bit overrated. The knife can be tested to perform as it should for it’s given purpose.
 
AndrewC said:
Sure, I could make 1.5 knives and that'd pay for the Grizzly, but that's not quite the point.
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If your selling knives for over $600 each then this is exzactly the point. You owe your customers the best.

What I meant was you go into a dealership and want to buy a car. You ask the gas mileage and thy say i dont know. Hardness testing is just a quality control step that shows what your doing is corect and you can prove it. There are times when I have gotten unexpected results with a heat treat process. I would have sworn it was X hardness but the test showed something much lower.
 
I need to say this becaus I think I am being misunderstood. I am not saying you can’t make good knives if you dont have a hardness tester. Lots of smiths dont have hardness testers and make great knives. My Customers expect a knife that is above and beyond something thy can buy at Walmart. It’s a quality control item that just makes sure I’m where I think I am.
 
Depending on your personal ethic and what chunk of the market you are targeting, it may well be a nice marketing point. If you are selling kitchen cutlery (especially in a japanese style) it seems many folks are very concerned about a numerical hardness. I don't place a lot of value in knowing the hardness number by it self (as in this knife is at 62 HRC, but you still don't know the details of the heat treat process). I have seen a bunch of chipped kitchen knife edges on knives that claim hardness values (low-mid 60s) that should be tough and very resistant to chipping. But that being said, people in this market (at least the ones I have met) seem very taken with this number as if it is the end-all be-all.

Anyway, you can do as Stacy suggests, file and rod test the knife and know it is about XX HRC (depending on steel, HT, and Temper temps). For instance a 400F tempered 1095 blade should be in the neighborhood of 62.5 HRC. It may be reasonable to bill said knife as 62HRC without testing it empirically. With a good HT, it would be so close that nobody would call you on it. That isn't something I like to do. If I were to tell someone a specific numeral HRC value, I would have wanted to have tested it (not to say that I don't buy the counterargument)

Anyway, if you do want to use it for marketing and are like me in that you would not like to give a specific number without verifying its specific voracity, you could think of it as in investment in marketing as there is definitely a market segment who is more likely to buy a blade of identical quality that is billed as "HRC 64.5" in lieu of "Rockwell Hardness in the mid 60s C scale".

If you are not selling to a crowd that cares about hearing those numbers and you are testing your blades sufficiently, It would seem to me that investment in this device might be less wise or simply a curio.

If you are in the business of HTing anything someone sends you, I would think that having a tester would be critical for fine tuning your HT on any steel that you may encounter.
 
Rockwell hardness is like megapixels in digital cameras. It is a number that the customer has some limited understanding of even if it isn’t a complete representation of properties.

For a knifemaker, however, it allows you to ensure consistent quality, to target specific heat treatments and sets of properties, and a better ability to understand heat treating parameters. I’m an engineer, however, I hate the idea of making anything without being able to measure its properties.
 
Patience and ebay, my friend. A hardness tester is a great tool for piece of mind and experimentation, but like many have said it not something you have to have.
I watched ebay and managed to pick up a functional h150a (grizzly type) for 450. I've seen many others get close to the same deal. The Chinese clone of the Ames can be had new for around 650. From what I hear on this forum they are great tools.
So, around 500 bucks is really what you are looking at forthe industry standard testing method. I'd say that is between $125 files and $3000 testing machines.
 
JTknives said:
I scored a rams Rockford for like $100 It does not use weights but a spring as the weight. It’s never needed adjusting once I calibrated it and left it in the 70° man cave. But temp can affect it, that’s why I leave it inside where the temp is regulated.
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I got one of these a while back for about the same money and have not been happy with it, sometimes reads good and sometimes its way off. I just figured it was junk and it has sat in the corner since. But the temp swings in my shop are large ... I am going to take it into the house where it will be more stable and give it another shot
 
Is yours the full size one or the mini one? Mine is the mini and I LOVE it. But I had found that on mine that the first 2 tests are a tad low by like 1rc. The 3rd is bang on. So that’s why I do 3 test on the gage block and then test a knife.
 
its about 2.5 feet tall and weighs maybe 40 pounds. It has sat on the shelf looking important for a few years now. Just a couple weeks ago I decided to try it again, I tested some pieces and it seemed to do real good and a few days later it was not even close ? I will move it to a more stable environment and see what happens.
 
Spalted said:
its about 2.5 feet tall and weighs maybe 40 pounds. It has sat on the shelf looking important for a few years now. Just a couple weeks ago I decided to try it again, I tested some pieces and it seemed to do real good and a few days later it was not even close ? I will move it to a more stable environment and see what happens.
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Yeah full size one. Move it to a stable location with a stable temp and I bet you will be surprised.
 
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