is the brass rod test reliable???

farmrbrnboy

Active Member
I was reading in the $50 Knife Shop and Wayne Goddard discusses the 1/4" brass rod test. I tried it on my 9260, 5160 and 1095 blades and they didn't pass. Then I tested a Mora knife, Imperial M10 bayonet, Alabama damascus blade, 9260 Cheness sword, all did not pass. The only blade that passed was a Benchmade ATS34 blade. The 5160 and 1095 blades will chop through a 2x4 and still shave. Is the 1/4" brass rod test reliable? I used a pyrometer in my forge and heat treated according to Kevin Cashen's recommendations.
 
Which way are all these blades "failing"? Are they folding over or chipping.

As a short answer to your question, I would suggest that the brass rod test is a useful tool which requires interpretation in both application and conclusions.
 
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Just my 2¢ worth, no. Not the way the Wayne Goddard showed it. Try to drive the blade through a thing rod, 1/16", or some soft iron wire and see if it indents. If it's chipped out then the steel is too hard; if it's pushed it with a rolled over edge it's too soft. Nothing more than a slight flattening of a thin edge.

Doug
 
There are so many variables in how one does the test. Yes, it can be reliable and Yes, the test can fail.
Take what you can from this test and adjust the way you see improvement.

Its like people that say, My knife is sharp enough to shave hair after I sharpen it so there for its a excellent cutting edge. not necessarily, Shaving is a push cut and cutting with a knife is a draw cut. so while shaving is a indicator it's not the final word.

Laurence

www.rhinoknives.com
 
Farmrbrnboy, is it reliable- it depends. It depends on what property you are trying to measure with it. Any test is only good if one knows what it can and cannot measure when applying it and the brass rod thing is one of the most misunderstood of all tests that bladesmiths often use. It is often used as a replacement for something like a Rockwell test for measuring hardness, for which it is all but useless.

Hardness is actually not a property unto itself but more a method for us to quantify a certain type of strength in the material. In a very general term strength is the materials resistance to deformation. There are two modes of deformation, there is plastic (permanent upon removal of the load) and there is elastic (not permanent and things will go back to original shape when the load is removed). Nothing in the elastic mode can really give us an idea of true strength because elasticity it is a property inherent in the material that is separate of hardness, e.g. a dead soft piece of steel will flex exactly the same amount as a fully hardened one under the same load so long as the force does not exceed the elastic limit. So in order for the brass rod test to really tell you anything about the heat treatment you need to exceed the flexing range and either break it or bend it, and then you still have no quantifiable representation of the result. Should a piece of steel flex even a bit under a Rockwell major load the test is worthless because it can only measure permanent deformation to give you any idea of the strength we see as hardness.

Does this mean the test is not reliable for anything? Not at all. What it can give us some input on is our edge geometry and grind. It has been said that a similar test was used in the old days in German Cutlery factories, this is true. But where the guy who did the test stood was behind the guy grinding the blades to insure that the edges were of a uniform grind within tolerances that they were shooting for. A thin edge will flex father with much less force and will generate much less tensile/compressive strain to do so.

Even if you automated the rod test so that you actually generated accurate standard numbers on degrees of deflection under a given load, it would still mean nothing for analyzing heat treatment as soon as you changed the grind just a bit and all the numbers changed on you. You may have a blade that is too brittle according to the brass rod, but too brittle for what? And too brittle for what edge geometry? An axe with a standard axe heat treatment is almost indestructible due to its edge geometry to match the heat treatment, but if you ground very fine skinning knife or scalpel edge onto that axe the heat treatment will be entirely too soft to support its edge; exact same hardness level but one edge rolls like lead while the other can chop down an oak tree.

My concern is that if you are following my recommendations on those steels, depending on your temper, you should not be seeing the steel fail in such a ductile mode when it exceeds the elastic limits. But then again it would all depend on your edge geometry for a given hardness.
 
So what is a better alternative to testing if the draw is where we want it? I cut a strand of romex 1/16 copper.
 
The blade on the slack belt on the edge is around 30 degrees. 5160 was tempered at 350 degrees for 2 hours x 2 and the 1095 was tempered at 450 degrees for 2 hours x 2. I have a hard time judging 35 lbs of pressure. With my body type and exercise program, I'm probably pressing alot more than needed and with my old eyes, I'm not detecting deflection until it is really obvious. Maybe chopping through 1/16" copper would be a better test.
 
Farmer is this a chopping blade? I would reckon at 30* you would have a had time flexing the edge. I interested on what Kevin and others would recommend as a better alternative but I figure a knife is for cutting so in my simple thinking a cutting test would be good is why I chose the romex.
 
Zombie chopper, camp knife. I did make a EDC with approx 22 deg convex, that one flexed real easily. I was able to chop through #12 copper wire, which is approx 5/64" with no damage to the blade on all my knives. Even the Mora with a Scanti grind, which flexed the most and remained flexed was whacked through the romex with a slight indentation to the edge. At least with chopping through romex alot of variables are decreased, angle of blade to rod, amount of pressure applied, good eye sight/lighting to verify flexing of blade and angle of the grind. With the romex, angle is perpendicular, force is the same to cut throught the wire, if it only takes 30 PSI to chop through and if you apply 50 PSI, the blade is already through the wire and into soft wood. Maybe someone with all the scientific equip can develop a test chopping through #12 copper wire.
 
As with some of the other more subjective/experience type in shop tests, you really need something to compare to,... a control group of other knives of known quality, hardness etc, with similar geometry. It's also a good idea to use other types of tests in conjunction with it because it's not a very conclusive test in and of itself. I've never had a blade fail this test, but if one ever did, I'd suspect something was wrong with it.
 
Even if you automated the rod test so that you actually generated accurate standard numbers on degrees of deflection under a given load, it would still mean nothing for analyzing heat treatment as soon as you changed the grind just a bit and all the numbers changed on you. You may have a blade that is too brittle according to the brass rod, but too brittle for what? And too brittle for what edge geometry? An axe with a standard axe heat treatment is almost indestructible due to its edge geometry to match the heat treatment, but if you ground very fine skinning knife or scalpel edge onto that axe the heat treatment will be entirely too soft to support its edge; exact same hardness level but one edge rolls like lead while the other can chop down an oak tree.

My concern is that if you are following my recommendations on those steels, depending on your temper, you should not be seeing the steel fail in such a ductile mode when it exceeds the elastic limits. But then again it would all depend on your edge geometry for a given hardness.

To some, Kevin's words might not make sense....but once you develop an understanding of the associations of steel type, hardness, and grind geometry, he is spot on! Personally I use the brass rod test, and put a lot of emphasis on it's results to judge where the blade I'm working on stands. As with any type of "testing" for custom knives, the individual must establish his/her standard(s), and the testing for those standards. Along with that, actually using a given knife for it's intended purpose(s), SHOULD play into a makers testing. Many times I get very frustrated with folks who demand "scientific" or "empirical" evidence when it comes to custom knives. That's a very elusive thing.....we each have so many variables in our shops, ranging from our forging and grinding techniques, to the heat treating methods we use, that there is a very tiny likelyhood that one persons methods could be EXACTLY repeated

Kevin put it very well......two short articles I've written attempt to do the same thing...... 1. http://www.caffreyknives.net/top.htm and the second is MY explanation of the brass rod test....... http://www.caffreyknives.net/testingart.htm
 
I think the main variables are geometry, steel quality and heat treating. Forging could also play a role,... lesser maybe, but still something to consider.

The test itself also has the variables of, amount of pressure or force applied and diameter of the rod.
 
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... I tested a blade (of a student) once that kept chipping out in the exact same spots up to about an inch or so behind the point, which was a bit puzzling… It was a 1095 blade, very hard with a very acute angle on the edge. I decided to etch it to see what I could see, and there were a few stringered inclusions right at those spots. If the blade had been forged to a point rather than cutting across the grain flow, they probably wouldn’t have been a problem, but in this case it was from thin stock and somewhat impractical to forge the point without modified technique. In this scenario, we just raised the temper and brought the edge angle up a little.

… The most outstanding feature of a knife is it’s edge. If we stop and really think about the edge,… there is an extremely miniscule and minute amount of steel riding along the very edge of a hair popping blade.

It’s hardly even there, but for a single row of grains…. So, down at that level in a sense any flaws, inclusions or defects in the steel etc., become “magnified“.
 
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Thanks for the links Ed and very well put as too. Good reading and information from Tai and Kevin as well. Thanks
 
So if 35 pounds is applied to the edge and it showed elastic deformation for a given edge geometry, can enough force, say 45 pounds be applied and the edge show plastic deformation with the same given edge geometry? Could it be that I am not seeing the blade flexing and applying too much pressure? If that is the case, I may need to bump up my reading glasses a point and get better light.
 
If you put too much pressure they’d all either chip out or curl at some point… seems like.

I think the test really works best on blades with thin edges, like kitchen knives. On thicker edges it get real hard to see… if noticeable at all.

It gets back to what I was saying about needing something to compare to, and some experience.

Chopping into the bass rod can also be somewhat tell tail, if you have something to compare with. With this test it also helps by shifting the angle from straight on to say about 45 degrees.
 
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I have had a 100 percent positive experience with the brass rod test. Every blade I've tested passes, from $10 kitchen to $100 folder. This is why I don't really find it to be a useful test.
 
I don't use it much any more either, for that same reason. The same types things can be determined other ways. There’s a place for it I suppose though.
 
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