The Brass Rod Test

[Scott Roush]

I was just reading on another forum that the brass rod test isn't necessarily a reliable test for your heat treat, but rather your edge geometry.  But then it goes on to say that if you really screw up your HT... then the brass will chip or deflect (permanently) your edge.  So... Just wondering what other folks think about this and whether or not others use the brass rod.  To me... at my stage as a beginner, I guess I would be happy to find out that I didn't really screw up the HT.

Also... Is there a best way to use this test? I've basically been bearing the edge down on the rod and looking closely at how it deflects as it goes along the rod... and then inspecting for any deflections that hold... or any chips.

Thanks!

[Lin Rhea]

The brass rod is a good test for all of the reasons you mentioned, but it's not the only test. I always do some chopping on a chunk of Osage. Some knives are rather small and the chopping is not a thorough test. They just dont have enough length or swing momentum to test it. The brass rod is good for those.

A good knife maker will be concerned with a LOT of things, but here it boils down to some very basic things. Heat treat and geometry primarily. Those two things can be tweaked Up or DOWN to meet the needs of a particular knife usage. Test often and in more than one way. Lin

[beaver#1]

i have never used the brass rod test.  i know about it but just dont use it.  my test is once through with HT i get the cutting edge sharp enough to shave a little. dont have to razor sharp just pretty sharp.  get a big peice of osage or i have heard to a deer antler works great and just hack at it.  make sure to go up and down the blade then inspect.  any chips, waves or big curls, then you did something wrong in the HT. also after i do this i still want it to be able to shave a little just like before i started.  hope this helps some

[Lin Rhea]

I want to make something clear, even after I just saw Dustin's post. Dustin your doing it right, but in addition remember this.

Sometimes testing to failure is not the same as a bad heat treat or that something went wrong in the heat treat. Sometimes the edge may fail when you have a perfect heat treat. Remember the basics, heat treat and Geometry. You have to be able to recognize which one is failing and correct only that. Some guys end up chasing their tails and not getting it done.

If you roll you cutting edge down pretty thin and chop, it will probably fail. How it fails will determine your next move. If it chips, you know it is indeed the heat treat and you will have to draw it down a small amount to soften it. If it rols or deforms slightly, you know the blade's not too hard, but NOW you have to determine whether it's one of two things, either too soft or too thin.

   I personally like to test to failure on every knife blade. Then work up to the right combination of heat treat and geometry for the given type of knife. Lin

[Scott Roush]

Thanks guys. This helps a lot.  Just so that I understand... When doing a brass rod or any kind of chopping test... If it chips... no matter what it's the HT.  And if it rolls or deforms... either soft or too thin. Right?

I'm now starting to realize that I need a better grasp on what constitutes good edge geometry. So far I've only been concerned with getting as sharp of an edge as possible.  Is there a 'completely wrong' edge geometry or does it come down simply to what the usage of the knife is???

[Lin Rhea]

Thanks guys. This helps a lot. Just so that I understand... When doing a brass rod or any kind of chopping test... If it chips... no matter what it's the HT. And if it rolls or deforms... either soft or too thin. Right?
 

Yes, in a nutshell.

It's the knife's usage. However each maker seems to have a favorite geometry. I like a flat grind with an appleseed edge. On a large knife that is likely to see chopping, I will leave the edge slightly thicker, say 45-50 thousandths before rolling in to the cutting edge in a distance of about 3/16 of an inch. A hunter is thinner, maybe 25-30 thousandths. This is where a maker needs to spend some time chopping and cutting different mediums to know what works for different situations. Lin

[kbaknife]

Originally posted by Lin Rhea:
.........Remember the basics, heat treat and Geometry. You have to be able to recognize which one is failing and correct only that. Some guys end up chasing their tails and not getting it done.

 Lin

The more time a person spends in his forge and in his shop, it will become clear just exactly how HUGE!!!! that statement is that Lin made right there.
He just said two words, "...heat treat...." that sometimes takes literally YEARS to get a grasp on.
"Heat treat" begins at the forge with known steel and carries all the way out and through final tempering, including proper heats during forging, thermal cycling, normalizing, spherodizing, austenizing, quenching, temping, etc.

Flexing a knife's edge over a bar of steel is interesting to say the least.
But what is it you are flexing? What steel is it? How was it heat treated and ground? What's its geometry?
All of these tests are fine and good, but to know what it is you are testing, just get yourself ONE GOOD KNOWN STEEL.
Work with JUST THAT STEEL until you LEARN IT.
Learn one grind. Make one knife.
Over and over and over again.
Once you've got a good grip on that, then "testing" will have some value, because you'll be "testing" a repeated process and it will make sense.
Don't fall into the trap of depending on only a few criteria to determine success in such a HUGE field of endeavors.
Reduce your "zone" from the get-go.
I certainly don't mean to discourage anyone with their knife making, but just realize that your success will depend on what you want out of it.
If you really do want to make the best knife you can, then slooooooooooow down.
One thing at a time.
I swear that when I started making knives, I had a guy tell me that it takes 25 years to become an excellent knife maker.
I thought he was kidding.
I don't any more.

[Scott Roush]

That makes a lot sense Karl. Thank you.  I had already started thinking a bit the last couple of days on trying to focus on a steel and a grind... Your post just brings that to a head...

[kbaknife]

Don't know how that double post happened.

[Jeremy]

EDIT: Sorry, not the best place for my post... I moved it elsewhere.

[Scott Roush]

Good points Jeremy!

However... when I get into something, I become very interested in how to achieve the best possible results... and I do have an interest in pursuing this beyond the simple hobby stage. But at this point, without anybody to learn directly from... I'm just trying to find some objective criteria that will aid me in determining the quality of the work I'm doing right now.  And, as Karl mentioned... it is difficult without a longer term set of experiences in which to compare 'success' to 'failure'. That is one of the reasons I liked the idea of the brass rod test over just skating a file over the edge.   But... I guess you can't get more objective than simply chopping on some hard wood and just plain using my knives at this point...