brass rod

Do you have a copy of Wayne Goddards books?? It is covered there but here is a brief description. Once the blade is hardened and tempered sharpen the blade. Place a brass rod in a vise horizontal. Press the edge against the brass rod from the side of the blade. You should see the edge flex and then return to straight if it is HTd correctly. If it chips out the edge is too hard if it stays bent from the pressure it is too soft. Red o proper steps to get the correct hardness.
 
It's simple after you have heat reated tempered and sharpened your blade take a 1/4" brass rod and put the edge sideways on it push down and see if the blade flexes and returns to normal wich is what you want. If it stays bent it.s to soft and needs to be re heat treated and if it chips a chunk out it is too brittle and needs to be tempered again at a higher temp.
 
The blade does not need to be finished (actually it should NOT be finished) when you do the rod test. Just grind a quick thin edge and test it. If it is too hard, re-temper at 25 degrees higher temp. If it is too soft, re-harden the blade. Remember to dull the edge after testing - unless you like getting cut while finishing blades.
Stacy
 
Since the Modulus of Elasticity is the same for all steels, whether hardened or not, I believe that the brass rod "flex test" is dependant on the edge geometry (thickness), not the heat treatment. I guess if you really overheated the heck out of the blade or failed to temper it, it might well chip out as you flexed it. However, if you didn't heat treat the blade at all, it shouldn't stay deformed unless you needed a lot of pressure to flex it in the first place (hence the edge thickness factor again). Please correct me if I'm wrong.
 
Hey Chris, here's an answer that I got from Kevin Cashen when I queried the group a few weeks ago in the "Rehashing Flex" thread:

Kevin R. Cashen said:
The edge flex thing is like the file test, adequate if you are not all that particular. It will get you in a wide range but will not tell you anything specific. I would say that the file test can be more accurate since it at least measures a form of hardness (abrasion or scratch hardness but not penetration), while the brass rod flex test tells you a whole lot about how thin you ground the blade and not as much about heat treatment as people would like to think. People who hold it up as the definitive test are simply blowing hot gas. The only way the test can tell you about heat treatment is if you push it to the point of yielding and then you have a kink in your edge- kind of like the nice fellows in the middle ages who would tie rocks to your daughter, toss her in pond and then tell you the great news that she was not a witch after all! Hey that’s great, but it is rather moot point now isn’t it? And of course if you have a good hardness on your edge it will flex like crazy if it is thin. Are we looking for a certain amount of deflection every time? Are we looking for a certain amount of force required every time? If it is a set amount of deflection forget about however you heat treated it and just grind it thinner to meet your mark. If you want to really lay on it and not deform it at all simply grind it thicker. I personally think there has been a lot of slight of hand and misdirection involved in many of these popular tests that make the presenters knives look great, either in their own mind or in the public. Flexing over a rod will get you inside a huge ball park if that is all you need, but it is not a real definitive or even accurate test overall.
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If you flex the edge and it chips you know it is too hard. You may not know if it is too soft but when paired with the file it is just one more test that helps show the blade is properly done. Is it the absolute best? Of course not. Pushing the knife in cut testing is by far a better test. It does however give you a better idea than just using temperature alone or just the file test. It can lead to Hype but that is not the purpose.
 
Mr. Richards, I agree. If any test is all you got it sure as heck beats no test at all, and it would be just plain foolish to go without it just out of spite because it is not the best test around. I personally could never bring myself to say something as outlandish as suggesting if folks can't buy a Wilson Rockwell tester that they should forgo testing altogether, and I doubt anybody else here would. I do believe that just as important as testing is knowing the faults and limitations of any given test however, so that you know how far to trust it and where to go next when you feel you are not getting the results you really needed (note- "needed" not "wanted"). Heck visual inspection is a very valuable test that every one of us use, but it won't tell you squat about hardness, internal conditions, microstructure, heat treat, impact strength, brittleness, ductility, abrasion resistance etc… , yet I don’t think there is a single one of us that is ready to abandon it or suggest not doing it, we just need to realize its flaws an limitations. But I would get very uneasy if anybody left the impression that we can just stop at visual inspection because that is good enough. I think, I hope, the other gentlemen who posted here are merely saying the same in regards to flexing over a brass rod.

Matt those are indeed my words from a few week back, and I stand behind them still, but for folks to pile on me for it after any conversations since would be tantamount to double jeopardy wouldn’t it?;) The reason I said that was frustration from that nasty itchy feeling I get on the back of my neck whenever an eager new smith is looking for really good advice and very limited tools or methods are held up as definitive. Just because we don’t have access or interest in more precise methods doesn’t mean we should write them off as unworthy of pursuit; that is nothing more than sour grapes, which is not bladesmithing or science. If you look around and nowhere else in any steel working industry is a method used, you may want to really check the details and facts about it before proclaiming it the standard. Getting by with what you have is what it is all about, but understanding the limitations of what you have and how you cam improve it is essential for personal progress. Denying the flaws are there doesn’t work in making better knives I doubt it would in any other area of the process.

When 5 smiths in Atlanta point out the problems in an ABS guys knives he can get defensive, tell them they are wrong and that his knives are just fine and keep making the same knives for the next 20 years. Or he can understand that he is there to find those scratches and gaps, whether he cares to follow the ABS approach or not he can always benefit from finding shortcomings and dealing with them as opposed to declaring his blades as having no problem because those judges standards just don’t apply to him. Even though it is easier to grasp that isn’t even a good analogy since it can deal with matters of taste an preference, while testing materials properties leaves no room for taste or opinions only cold, undeniable data, and the best tests were developed to eliminate our opinions an interpretations. The Rockwell dial doesn’t give a rip if you were wishing for 60, it simply reads 48 and leaves you to deal with that number.

It has been rightfully pointed out that that number is worth no more than a flex on a brass rod if you don’t keep it in perspective and properly interpret it.
 
Kevin: I have to say I agree with your thoughts. Test with what you have, compare to a reference blade and keep good notes and know the limits of your test. The temperature of your shop when doing the test is a significant variable. Flex a blade at 70degrees, the again at -20 and note the difference.

One Question I have, Why a brass rod? Are we afraid something harder than brass will somehow hurt the steel? You can use a large nail spike, any steel rod such as an old smooth sharpening steel. I believe one great maker used to shave old pistons that he later used for knife handles to test for cut.
 
Hey Ed, believe it or not- right back at yah! I have been thinking throughout this thread and others why it is always decribed as a brass rod? If the blade will get all gouged up by a soft steel spike, you may not need to flex since it appears to be too soft. Temperature will have heavy effects on impact strength, but it is also one thing that can have some effect on flexibility. The sub zero thing would be familiar to us in a long lasting Michigan winter as it would in Wyoming I am sure. I know it is the same months but this winter seems like the longest in years for me, I really don't know why I live here sometimes.
 
Kevin R. Cashen said:
Matt those are indeed my words from a few week back, and I stand behind them still, but for folks to pile on me for it after any conversations since would be tantamount to double jeopardy wouldn’t it?;)
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Such are the times we live in, my friend... mayhaps I should have allowed you the chance to respond on your own, but I figured, since I couldn't possibly paraphrase it any better, I might as well cut and paste it - thereby eliminating the chances of you crying "plagiarist!";)
 
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