View Full Version : Value of RC Hardness on Blade?
06-28-2011, 09:11 PM
I recently picked up a Rockwell C tester and am debating whether to put rating on my blades. RC is a + or - 1.5 rating but still is indication of edge holding ability, though not wearability or toughness. Seems to me this is of value to be etched on blade, but you don't see it done much if at all anymore. Do makers think end users are too ignorant to appreciate the rating therefore don't put on blade and extra writing detracts from look of blade??? Just wondered what other makers thought of this practice.
06-28-2011, 09:21 PM
Plus or minus 1.5 Rc points seems pretty big. There's a huge difference between 57 and 60.
06-28-2011, 09:37 PM
True and I think you can get within 1 point if you follow manufacture's instruction for instrument including having a testing standard and use NIST guidelines. The + or - 1.5 is a worst case- point being that RC testing has a lot of variables and requires good procedures to do accurately.
06-28-2011, 10:11 PM
I understand. I've never used a Rockwell tester myself, but I'm told it's wise to spend the money on really accurate calibration blocks. Perhaps that would help to narrow it down to a point or less?
Kevin Cashen has written on this subject here and over on BladeForums, maybe try searching his name. He's done a boatload of work on this topic.
Anyhow, I doubt I would mark the Rc value on a blade, but I do include it in descriptions and the invoice I send with it. (my HT is all done by Peters' HT, they Rc test each blade for me)
06-28-2011, 10:15 PM
James, I'm okay with my process...just wondering what other makers thought value was of putting the number on the blade....thanks for your input on your process- that is a good plan I think.
06-28-2011, 10:43 PM
I would be more concerned about someone claiming I put an inaccurate number on the blade.
Any type of "testing" is always done with specific equipment and conditions in mind.
All it would take is for someone else to do their "own" testing, with their equipment, then all of a sudden you have someone calling you unethical because the blade you said measured at HRC 60 was really HRC 58.
Not to mention that the results of the test are valid only at the point the test was taken. You take a test at one point on the blade, take another in a different location, and the results can be different, yet both still be correct.
Don't know if that's why you seldom see it anymore or not, but that would be my guess.
06-29-2011, 07:26 AM
Could be. I would never want to put anything on a blade unless I felt was true and my methods were sound, but there are always more sophisticated RC testing machines and methods than the one you're using and someone could prove you wrong and come back on you about it.
06-29-2011, 08:41 AM
just my 2 cents but for the guys who now knives and what they want i think they would ask or now what the range was for a given steel, and for the novice who buys a big box store knife like me before i started making i would not known or really cared as long as it cut pretty good. so you could ask the buyer if they would like it included on blade? so i say no i would not put on unless asked and then i would exsplain the + - to them.
06-29-2011, 06:29 PM
Sounds like common thought is that's it's a customer request thing or as James said is documented with knife but not etched on. Thanks for they input guys I think I'll leave it off there for one's I'm making to build my stock up here.
06-30-2011, 07:44 AM
Do makers think end users are too ignorant to appreciate the rating therefore don't put on blade and extra writing detracts from look of blade??? Just wondered what other makers thought of this practice.
I don't think end users are too ignorant....buyers are better educated today than ever before. But in another way I would answer yes. For years I have watched some makers taunt a Rc number as if it were the end all of their knives. What must be realized and understood is that a given Rc number, does not a knife make. I have tested Rc 57-59 blades, with the good geometry that out cut, out lasted, and were MUCH easier to sharpen than similar blades with Rc of 61-62. My point being that in many ways relying on a given Rc number to indicate anything about a knife is often misleading.
Over the years I have had countless individuals approach my table at shows and ask "What's the blade hardness?" After replying "Rc XX-XX", the comeback usually is..."I won't buy a knife unless it's at least Rc 61." (or some other ridiculously high Rc number). That's an example of where I say yes to your question.
I've come to realize that when an individual focuses on a Rc number, whether it be a maker of a buyer, it is a sure sign of inexperience to me.
No doubt that some buyers would like it marked on the blade, but I think most experienced knife buyers would see it as a sales gimmick/pitch. I also think that it COULD cause you grief, because sooner or later somebody will get the bright idea to have the blade tested for themselves, and if that test doesn't match exactly to what you've put on it, you've just opened yourself up for all sorts of grief.
06-30-2011, 10:25 AM
Good points Ed- maybe a more accurate statement would be that many end users are not too ignorant to 'appreciate' the RC number but many are too ignorant to 'interpret' the RC number in conjunction with many factors affecting blade performance such as how tempering was done, steel type, blade length and design, intended use, etc and cannot interpret how knife will perform using this number alone, though some assume they can.
06-30-2011, 10:50 AM
Ed, I'm starting to question if the cost of a hardness tester is worth it. In the end it is only one method that can tell you if the blade is hard enough to make a good edge. It seems like performance testing is the proof of the pudding and than any hardness testing would have to be interpreted in relationship to it.
06-30-2011, 04:17 PM
I suppose it's all in how each knifemaker looks at it. There are some makers who place all their emphasis on the Rc number(s), and really don't take anything else into consideration. There there are those makers who rely on testing a blade in real world conditions, and use the Rc number(s) as a "guide" only.
There was a time during my knifemaking career when I fell into the hole of things having to be a specific Rc number....but that was a long time ago, and at a time when my experience was very limited. Time and experience have taught me that those who place a great deal of emphasis on Rc numbers are often folks who just don't have the experience to know any better.
I also spent a lot of money taking blades to the local college for Rc testing......after about 6 months, it dawned on me that I was wasting my money because by that time my methods had become so predictable.
My personal opinion is that I could buy a lot more useful things for the shop than a Rockwell tester. I see it like this.....the Rc number of a given blade is nice to know, but it really doesn't mean a hill of beans.
07-01-2011, 08:25 AM
I agree fellas, an Rc number by itself only tells us one part of the story, and could actually be very misleading. Different alloys, and different blade geometries will perform to their best potential at different hardnesses... maybe one shop's Rockwell is calibrated for a certain range and not accurate in the range you're looking for... What if the Rockwell machine hits a vanadium carbide, that would really skew your readings... OK that's a bit of an extreme example but I suppose it could happen.
I have all my HT done by Peters', and it's cool that they Rc each blade. That saved me a lot of frustration when a supplier (I won't name names except to say it wasn't Aldo, Tracy or Pop's) sent me a bunch of 416 labeled as 440C... Brad caught the difference (46Rc vs 59-60 like I asked for) and those 416 blades are in the scrap bucket, I didn't waste time and money finishing them. The other 440C and CPM-154 blades in the same batch tested right, and held up to my shop-testing... I have full confidence in them.
I do like Rockwell testing as a beginning point; but using a given knife design/geometry/alloy/HT the way it's meant to be used, then beating the snot out of it until it breaks is the only way to know for sure.
J S Machine
07-08-2011, 11:40 AM
I think that Rc #s only mean something based on the steel they are for. In other words, one knife made of a given steel at a given Rc # may be great, but another type of steel with that same Rc # may be bad or not satisfactory. Like Ed Caffrey said, when a buyer focuses on Rc, they are not very knowledgeable. Now if a buyer had done his homework and knew tha the Rc# advertised was good for the particular steel you have, then you might have something.
07-08-2011, 03:43 PM
If the RC value "is not worth a hill of beans" then what should I use to test blades? As JT stated sometimes you don't get the steel you ordered. What do you do when you make mosaic pattern welded steel blades? I would like a test method that gives me a number that can be compared to other knives. Most of the methods like impact testing and pulling samples apart are all destructive. So what are we left with?
07-08-2011, 07:11 PM
I suggest that you test them by use. After I have hardened and tempered the blade and put a rough edge on it I like to cut some soft iron wire with it. The edge should not chip out or roll over. If you are making a chopper, chop some 2X4" with it. Slicing some fiberous rope will test edge retention. There are places where a hardness tester may be useful but I don't know if it's worth the $1200-1300 for a used ames HRC tester. I may see if there is a service that will test for hardness around where I live and, if the price is reasonable, I might hire it out occasionally but not for every blade.
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