Brass Rod Test

J

Jemblade

Joined
Aug 29, 2013
Messages
143
I am post-HT with some skinners than I made out of Aldo's 1084. I have done my finish grinds and I have not sharpened them yet. I did a brass rod test on them and the rod did dimple the edges. With this info I knocked the edge down and kept them a bit thicker. I don't have a micrometer, but suffice it to say the edges are thinner than a business card. The edge does not dimple now, but flexes and returns to shape. Now I understand that the brass rod test is imperfect, but does this indicate that my HT was unsuccessful and perhaps I am getting better results now that the edge supports itself better or that I had initially ground the edge down too thin?

By the way I am using a 2 brick forge using the magnetic testing method, so it is not an optimized setup. But, I did follow Stacy's recipe for this HT.
 
Without photos or measurement it's hard to say. I suspect most steels, even with proper HT, when ground too thin will deform at the edge. If you had ground the edge back to "reasonably" thin and it still deformed without returning I'd say your HT was not good or your temper was too high. If it is springing back nicely now you probably have a decent HT. If it was chipping you could temper it down a bit.
 
i4Marc said:
Without photos or measurement it's hard to say. I suspect most steels, even with proper HT, when ground too thin will deform at the edge. If you had ground the edge back to "reasonably" thin and it still deformed without returning I'd say your HT was not good or your temper was too high. If it is springing back nicely now you probably have a decent HT. If it was chipping you could temper it down a bit.
Click to expand...

It was not chipping. I will put the original thinness of the edge this way... Part of the edge was uneven (some areas were thinner than others) I wasn't paying attention to what I was doing and the next thing I noticed part of the edge was gone. I had ground it to beyond zero. :D

So there is a limit to the thinness that the edge can be before it will deform regardless?
 
I can't speak for all steels. But I have ground a couple of knives thinner than what would be practical for the intended use. In those instances testing showed some edge deformation. I ground the edge back slightly and resharpened. Then they cut like champs and passed the brass rod test with flying colors. Just as a side note, the brass rod test was not intended to be a good test for all knife types.


The Brass Rod Test (as it appeared in BLADE Magazine) by Wayne Goddard

The brass rod test was demonstrated to me in 1959 by an old blacksmith who made knives in the 1930s. Here is my version of the brass rod test which is simple test of heat treating to help determine that a blade will hold up in normal use.

Clamp a 1/4-inch-diameter brass rod horizontally in a vise with the top half above the jaws. Or glue it to a piece of hardwood. Lay the knife edge on the brass rod at the same angle used for sharpening (about 15 degrees). Have a good light source behind the vise so that you can see the deflection caused by the rod on the edge. Apply enough pressure so that you can see the edge deflect. (When tested on a scale, the pressure works out to 35-40 lbs.) If the edge chips out with moderate pressure on the rod, the edge will most likely chip out in use. If the edge stays bent over in the deflected area, it will bend in use and be too soft to hold an edge. The edge of a superior blade will deflect on the rod and spring back straight.

The test is intended for knives in the hunting knife class. Thin filet knives or thick camp knives will not respond to the test in the same way. The blade that is too hard will chip out in normal use, too soft and the edge will bend. The brass rod test can quickly determine if the blade has a good balance of flexible strength and hardness sufficient to hold an edge.

The brass rod test as I present it is not intended to replace a hardness test to determine that a blade was fully hardened. It only applies to blades that have been tempered. I have worked out my version using it on blades made of alloy and carbon steel types that backyard heat treating methods are adequate for. The brass rod test is only a comparison test to determine what is in my opinion a hardness that will hold up in normal use. I started using is about thirty years ago and still think it is the best non field-use test I've found for testing the suitability of a blade steel and heat treatment for a working knife.
 
I do this test on a Butcher's steel that I have smoothed to 600 grit. If I see it ripple and return as I pass the edge over the smooth steel at an angle of 20 degrees or less depending on the knife and its function, chances are its fine.

I don't heat treat my stainless steel blades. I send them to Buck knives.
But i grind post HT so I use it to make sure that I haven't over heated the steel during grinding.

You will develop an idea for what the rod test is telling you the more you use it.
 
i4Marc said:
I can't speak for all steels. But I have ground a couple of knives thinner than what would be practical for the intended use. In those instances testing showed some edge deformation. I ground the edge back slightly and resharpened. Then they cut like champs and passed the brass rod test with flying colors. Just as a side note, the brass rod test was not intended to be a good test for all knife types.


The Brass Rod Test (as it appeared in BLADE Magazine) by Wayne Goddard

The brass rod test was demonstrated to me in 1959 by an old blacksmith who made knives in the 1930s. Here is my version of the brass rod test which is simple test of heat treating to help determine that a blade will hold up in normal use.

Clamp a 1/4-inch-diameter brass rod horizontally in a vise with the top half above the jaws. Or glue it to a piece of hardwood. Lay the knife edge on the brass rod at the same angle used for sharpening (about 15 degrees). Have a good light source behind the vise so that you can see the deflection caused by the rod on the edge. Apply enough pressure so that you can see the edge deflect. (When tested on a scale, the pressure works out to 35-40 lbs.) If the edge chips out with moderate pressure on the rod, the edge will most likely chip out in use. If the edge stays bent over in the deflected area, it will bend in use and be too soft to hold an edge. The edge of a superior blade will deflect on the rod and spring back straight.

The test is intended for knives in the hunting knife class. Thin filet knives or thick camp knives will not respond to the test in the same way. The blade that is too hard will chip out in normal use, too soft and the edge will bend. The brass rod test can quickly determine if the blade has a good balance of flexible strength and hardness sufficient to hold an edge.

The brass rod test as I present it is not intended to replace a hardness test to determine that a blade was fully hardened. It only applies to blades that have been tempered. I have worked out my version using it on blades made of alloy and carbon steel types that backyard heat treating methods are adequate for. The brass rod test is only a comparison test to determine what is in my opinion a hardness that will hold up in normal use. I started using is about thirty years ago and still think it is the best non field-use test I've found for testing the suitability of a blade steel and heat treatment for a working knife.
Click to expand...

This is exactly what i had happen to me. I am hoping for the same result. That's a good read thank you.
 
Rhinoknives1 said:
I do this test on a Butcher's steel that I have smoothed to 600 grit. If I see it ripple and return as I pass the edge over the smooth steel at an angle of 20 degrees or less depending on the knife and its function, chances are its fine.

I don't heat treat my stainless steel blades. I send them to Buck knives.
But i grind post HT so I use it to make sure that I haven't over heated the steel during grinding.

You will develop an idea for what the rod test is telling you the more you use it.
Click to expand...

Noted. I guess that is where I am at in my discovery, not just getting a result, but really figuring out what that result means...
 
Jemblade said:
Noted. I guess that is where I am at in my discovery, not just getting a result, but really figuring out what that result means...
Click to expand...

The discovery in my case has continued and I hope it never stops!:) There is always more to do and earn about knife making, Testing ,,,,
 
Just to make it clear:

The brass rod test is done on a sharpened edge. It does not need to be stropped and polished, but it needs to be sharpened. A fairly thin and lower angle edge is best for this test. Normally, it is done on a blade immediately after the tempering and preliminary bevel cleanup. Put a "quick and dirty" edge on at a lower angle. 10° per side is good. I use the grinder and a 120 or 220 grit belt.

Place the blade on the 1/4" brass rod in the fashion indicated by Wayne Goddard. Start at the ricasso end and
draw" the blade down the rod toward the tip. You should be able to watch the edge flex as it runs over the rod. You apply just enough pressure to get a reasonably visible deflection. After that, check the edge for damage and rolling. A tiny bit of rolling is OK, but it should return to nearly straight. Some folks run the blade down the rod twice, flexing left then right, and then check.

It is mainly to test the HT of the blade.
1) Chipping equals too hard and brittle for the steel type. tempering at 20-30° higher should help. Resharpen and test again after a higher temper.

2) Bending and staying bent ( rolling) equals too soft a blade. Repeat the HT if the bend/roll is severe and has little or no return at all. If the edge flexes, and returns partway, make the final edge at a higher angle and a bit thicker. The cause of a rolling edge is that the temper may be too high or the austenitizing and quench was bad.

3) Flexing and returning shows a proper HT for the steel type.

Once the edge is tested, and any additional tempering and testing is done, dull the blade and finish the sanding and assembly.
 
Stacy E. Apelt - Bladesmith said:
Just to make it clear:

The brass rod test is done on a sharpened edge. It does not need to be stropped and polished, but it needs to be sharpened. A fairly thin and lower angle edge is best for this test. Normally, it is done on a blade immediately after the tempering and preliminary bevel cleanup. Put a "quick and dirty" edge on at a lower angle. 10° per side is good. I use the grinder and a 120 or 220 grit belt.

Place the blade on the 1/4" brass rod in the fashion indicated by Wayne Goddard. Start at the ricasso end and
draw" the blade down the rod toward the tip. You should be able to watch the edge flex as it runs over the rod. You apply just enough pressure to get a reasonably visible deflection. After that, check the edge for damage and rolling. A tiny bit of rolling is OK, but it should return to nearly straight. Some folks run the blade down the rod twice, flexing left then right, and then check.

It is mainly to test the HT of the blade.
1) Chipping equals too hard and brittle for the steel type. tempering at 20-30° higher should help. Resharpen and test again after a higher temper.

2) Bending and staying bent ( rolling) equals too soft a blade. Repeat the HT if the bend/roll is severe and has little or no return at all. If the edge flexes, and returns partway, make the final edge at a higher angle and a bit thicker. The cause of a rolling edge is that the temper may be too high or the austenitizing and quench was bad.

3) Flexing and returning shows a proper HT for the steel type.

Once the edge is tested, and any additional tempering and testing is done, dull the blade and finish the sanding and assembly.
Click to expand...

Perfect! Thanks as always Stacy!
 
Jemblade said:
Noted. I guess that is where I am at in my discovery, not just getting a result, but really figuring out what that result means...
Click to expand...

That's a very reasonable approach.

It's a "ballpark" kinda thing and a good place to start testing certain knives; at a given geometry, there's a fairly wide range of hardnesses that will pass the test. The brass rod test will quickly tell you if a knife is really bad. It won't necessarily tell you if a blade is really good for your purposes.
 
Perhaps you gentlemen can help enlighten....I was thinking the brass rod test consisted of two parts.

1. The flex test as Stacy put very well
2. The cut test. place the sharpened knife perpendicular to the brass rod and give it a good wack on the spine....the idea being to cut thru the brass rod without roll or chips.
 
I never heard of doing that and wouldn't ever recommend it. What possible proof of quality in HT would it tell?
 
You can cut through a brass rod pretty easily with a cold chisel, but a cold chisel doesn't make a very good hunting knife ;)
 
ok then. I suppose that answered that question!!!! only one step to the brass rod test!!!!! and I follow you james. Geometry would be the key component of cutting thru brass rod, or a nail. Not heat treat.
 
james terrio said:
That's a very reasonable approach.

It's a "ballpark" kinda thing and a good place to start testing certain knives; at a given geometry, there's a fairly wide range of hardnesses that will pass the test. The brass rod test will quickly tell you if a knife is really bad. It won't necessarily tell you if a blade is really good for your purposes.
Click to expand...

Understood. When you are working without a more controllable and repeatable setup (i..e. 2 brick forge) a ballpark result is just gonna have to be good enough ;)
 
You must log in or register to reply here.
Back
Top