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where to get an RC hardness test.
- Thread starter redd1981
- Start date
Not sure if thats a dig or not but I have a target in mind. I just want to know if Im even close.
EDIT: Thank you for the suggestions I will look around.
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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I think what mete is getting at is people commonly talk about "hardness" as if hard is a thing like money...the more of it the better. This has caused people to think that any blade that isn't approaching Rc66 is junk. Obviously, the harder the better - Right?
Hardness in knife blades is a balance with toughness, and the use drives the balance. Also, while 1095 may get Rc 65 and temper to Rc 62 for a blade, S35VN may only reach Rc 62 and temper to Rc 59 for a good blade. Even though the Rc59 blade is "less hard" it will outlast the 1095 blade in edge retention.
I hardened a batch of a friends blades along with a batch of mine sent to Peter's. When they came back and he saw the report on the hardness tests, he was disappointed and asked why they couldn't make them harder. I explained the above info, and told him I request most carbon blades at Rc 58-59, and stainless blades at Rc 59-60. He was polite, but clearly thought the blades would be poor. He finished them, and couldn't believe how well they performed. In the past, he had been hardening his blades and tempering at 300F. By Peter's doing the temper at a higher point ( and much better) the blades have a tougher edge, so he isn't chipping off his edges. Now they last much longer between sharpening.
Hardness in knife blades is a balance with toughness, and the use drives the balance. Also, while 1095 may get Rc 65 and temper to Rc 62 for a blade, S35VN may only reach Rc 62 and temper to Rc 59 for a good blade. Even though the Rc59 blade is "less hard" it will outlast the 1095 blade in edge retention.
I hardened a batch of a friends blades along with a batch of mine sent to Peter's. When they came back and he saw the report on the hardness tests, he was disappointed and asked why they couldn't make them harder. I explained the above info, and told him I request most carbon blades at Rc 58-59, and stainless blades at Rc 59-60. He was polite, but clearly thought the blades would be poor. He finished them, and couldn't believe how well they performed. In the past, he had been hardening his blades and tempering at 300F. By Peter's doing the temper at a higher point ( and much better) the blades have a tougher edge, so he isn't chipping off his edges. Now they last much longer between sharpening.
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That hardness measurement originally was a approximate measure of tensile strength !!
If we substitute chromium carbides with vanadium carbides we may not see a difference in hardness but performance will be different because the two carbides differ in wear resistance .
Yes we have a long list of properties to consider and we look for knives that combine the properties we want for the use it will see. The more you know about these differences the better you'll be able to say , 'I'd like that steel at that hardness '.
If we substitute chromium carbides with vanadium carbides we may not see a difference in hardness but performance will be different because the two carbides differ in wear resistance .
Yes we have a long list of properties to consider and we look for knives that combine the properties we want for the use it will see. The more you know about these differences the better you'll be able to say , 'I'd like that steel at that hardness '.
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Before I got my own tester, I would take blades to a local machine shop. They have a VERY expensive Wilson Rc tester there that they use for testing their own products. They would test blades for $2 a pop.
When you consider that even a Chicom tester like I bought, is going to ruin $700+ that price of $2 is stupid cheap.
Keep in mind you need the steel to be clean, and you will get the most accurate reading if you have a sample that is dead flat with parallel sides. Unless they have a crazy, fancy tester with funky anvils, they won't be able to test the blade bevels, just the flats (like the ricasso).
When you consider that even a Chicom tester like I bought, is going to ruin $700+ that price of $2 is stupid cheap.
Keep in mind you need the steel to be clean, and you will get the most accurate reading if you have a sample that is dead flat with parallel sides. Unless they have a crazy, fancy tester with funky anvils, they won't be able to test the blade bevels, just the flats (like the ricasso).
Willie71
Warren J. Krywko
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As an example I had a 1095 tanto chipping at just over Rc 60, but it was fine at 59. I make 52100 and 15n20 kitchen knives at Rc62, and they hold up well. Each steel has a sweet spot for certain applications (including geometry) that balances edge holding and toughness. As pointed out already, harder isn't better. I am just starting to get the hang of these subtle and not so subtle differences. A few failures teaches you a lot, whether poor edge holding, or lack of durability. I have made mistakes both ways. I now have some parameters that are working well. I even trained my brother in law to use a cutting board with the fine edged slicers I made him.
To the OP, I do not mean to derail your thread. Apologies in advance. I found out today I may be given a nice tester (can't remember the name) but that it will need re-calibrating. Will this be an expensive process or is it something you do yourself, you just don't get it "certified"?
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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By the nature of the test, Rockwell testers are sort of calibrated each time you use one. Most folks check them against their test block every so often.
Test blocks can be found on ebay and similar sites fairly cheap. You can also make your own by hardening a 3x3x.25" bar of 1095 and having it tested on a known tester that gives good readings. Mark that block with the results, and use it as a reference when adjusting your tester.
The thing to remember if you have your own tester is that it is just a number. Use that number to compare results from HT and cut testing on your equipment. What the actual number is, is less important than how the number performs in testing. The number only becomes significant to others if you are certifying a specific hardness for some reason. The numbers are also only significant to you and your equipment and techniques. Just because Joe does XYZ and gets Rc61 does not mean you will get those results, or that your tester will read Rc61 when you do them. However, if your results test out good, and your hardness readings are consistent, then what the reading is on your machine compared to Joe's isn't important.
For that reason, keep records. The results of a new HT regime can be compared to past and future regimes, and tempering results can be compared. Quenchants can be compared with ease. This allows future HT to be better adjusted.
A good technique to use if you have a hardness tester, is putting a coupon in with every batch of blades. A coupon is a small piece of the steel stock you are using on those blades - 1X2" is a good size. The coupon provides a flat surfaced comparison to the blade test if there is any doubt about the blade test results, as well as a permanent reference to that HT batch. HT the coupon along with the blade using all the same HT parameters, including temper. For best results it should have parallel sides, be about the thickness of the middle of the knife blade, and finished the same as the blade at time of HT ( 400 grit, sandblasted, Scotch-brite blue belt, etc.). You should drill a hole in one corner for HT purposes and storage (keep the coupons in numerical order on a big wire ring).
Stamp the coupon with a reference number to your log book. That way you can look and see that coupon #229 was 1084 bought from Aldo in September of 2012, and hardened with blade #73. If there is a problem with results from a knife, you can look up other blades that were made with the same steel batch and see if there is a similar problem, or if the problem is unique to that blade. If all blades from that bar of steel have the same problem, you can call Aldo and see if he has heard of similar problems.
Before testing after HT and tempering, you should sand down the unstamped side of the coupon to 400 grit in order to get an accurate reading. Any other process done to the blade should be done to the coupon ( soaking in vinegar to remove scale, etc.) If you are using good HT techniques and testing, the coupon should read the same as the blade made in the same HT. In some cases, it is the coupon alone that will be tested, as the blade may not provide a suitable surface for the test.
Note:
For really accurate records, do a quick hardness test on the coupon right after quench to get the as-quenched hardness to put in your log book, and then put the coupon in the oven with the blade for temper. This will provide a good reference to how much the hardness drops in tempering. Knowing that your quench gets Rc 65 ( or whatever) and then the blade tempers down to Rc59 is very useful info. In stainless or high alloy steels, you can test as-quenched, after cryo, and after temper to see any gains from the process. A test coupon is a wonderful thing
Test blocks can be found on ebay and similar sites fairly cheap. You can also make your own by hardening a 3x3x.25" bar of 1095 and having it tested on a known tester that gives good readings. Mark that block with the results, and use it as a reference when adjusting your tester.
The thing to remember if you have your own tester is that it is just a number. Use that number to compare results from HT and cut testing on your equipment. What the actual number is, is less important than how the number performs in testing. The number only becomes significant to others if you are certifying a specific hardness for some reason. The numbers are also only significant to you and your equipment and techniques. Just because Joe does XYZ and gets Rc61 does not mean you will get those results, or that your tester will read Rc61 when you do them. However, if your results test out good, and your hardness readings are consistent, then what the reading is on your machine compared to Joe's isn't important.
For that reason, keep records. The results of a new HT regime can be compared to past and future regimes, and tempering results can be compared. Quenchants can be compared with ease. This allows future HT to be better adjusted.
A good technique to use if you have a hardness tester, is putting a coupon in with every batch of blades. A coupon is a small piece of the steel stock you are using on those blades - 1X2" is a good size. The coupon provides a flat surfaced comparison to the blade test if there is any doubt about the blade test results, as well as a permanent reference to that HT batch. HT the coupon along with the blade using all the same HT parameters, including temper. For best results it should have parallel sides, be about the thickness of the middle of the knife blade, and finished the same as the blade at time of HT ( 400 grit, sandblasted, Scotch-brite blue belt, etc.). You should drill a hole in one corner for HT purposes and storage (keep the coupons in numerical order on a big wire ring).
Stamp the coupon with a reference number to your log book. That way you can look and see that coupon #229 was 1084 bought from Aldo in September of 2012, and hardened with blade #73. If there is a problem with results from a knife, you can look up other blades that were made with the same steel batch and see if there is a similar problem, or if the problem is unique to that blade. If all blades from that bar of steel have the same problem, you can call Aldo and see if he has heard of similar problems.
Before testing after HT and tempering, you should sand down the unstamped side of the coupon to 400 grit in order to get an accurate reading. Any other process done to the blade should be done to the coupon ( soaking in vinegar to remove scale, etc.) If you are using good HT techniques and testing, the coupon should read the same as the blade made in the same HT. In some cases, it is the coupon alone that will be tested, as the blade may not provide a suitable surface for the test.
Note:
For really accurate records, do a quick hardness test on the coupon right after quench to get the as-quenched hardness to put in your log book, and then put the coupon in the oven with the blade for temper. This will provide a good reference to how much the hardness drops in tempering. Knowing that your quench gets Rc 65 ( or whatever) and then the blade tempers down to Rc59 is very useful info. In stainless or high alloy steels, you can test as-quenched, after cryo, and after temper to see any gains from the process. A test coupon is a wonderful thing
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Good discussion on hardness testing. A couple other things I would add. Like previously stated the blade has to be flat to get a good reading. Best is surface ground or very flat sanding on a surface block. I use a 1/4 anvil to further minimize surface imperfections. Also any scale, carb or decarb will offset the reading so another reason for surface grinding. Changes in temp. will affect the reading due to the damper pot oil changing in viscosity. I found out years ago that the test block standard is kept by the original Wilson/Instrom/ Rockwell company. They are still in business and will provide the exact standard test block. Best to get one calibrated to the hardness range you mostly look at. Like 61 or so. Also as mentioned you can make other test blocks on your own based on the std. block. I have checked some off shore test blocks for guys just to see-- and have found some off as much as 2 RC. The point is if you are comparing your results to steel data sheet values or other makers or test labs then having the correctly calibrated block is important. Every one on the same sheet of music. My experience is that you cannot depend on temp. alone to predict the hardness you are going to get from the HT cycle. Thermocouples drift and even new ones will often be off as much as 3 to 5 %. That is easily 30 degrees at 1000 and that is enough to make a difference. If anyone has questions on their test block I will be happy to check it based on the standard. I also have checked blade steel coupons for other makers and just ask for nothing other than return postage and a clearly printed address return label. Best to contact me through my web site. Phil