edge/hardness testing

J

Justin King

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Nov 8, 2009
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For those without a real hardness tester, how do you judge the hardness and retention capabilities of your edges? I have never used test files and have heard too much conjecture about them to really trust them anyway.
I fancy that I can tell within a few points by literally trying to carve a sliver off of several test pieces of varying hardnesses but have never verified my findings in this.
Does anyone have an informal type of test that they find to be fairly reliable?
 
Hi Justin.
There is a test called "the brass rod test" that will let the maker know how his edge will stack up under hard use at least with regards to hardness. Simply sharpen the edge and press it hard against a 1/8" brass rod that is clamped in the vise and see if the edge chips (too hard) or rolls over (too soft). If it chips simply adjust the tempering oven slightly warmer and retemper. Test the edge after each tempering cycle until the edge flexes and goes back to straight again.
 
Bruce, could you elaborate a bit on what you mean by "..the edge flexes and goes back straight again." Also, is the edge pushed against the brass rod straight down (perpendicular to rod) or at an angle? Thanks.

Phil705
Winthrop Winthrop Washington Washington
 
Phil, my understanding of the test is that the edge is flexed, at an angle, over the brass rod. You watch the very edge closely. You should see the edge deflect or flex, then return to true. As Bruce suggested, if it chips out, it's too hard; if it deforms permanently, it's too soft.

--nathan
 
not a fan of brass rod test as you can have i wide swing in what hardness can pass depending on the edge geometry
 
silver_pilate said:
Phil, my understanding of the test is that the edge is flexed, at an angle, over the brass rod. You watch the very edge closely. You should see the edge deflect or flex, then return to true. As Bruce suggested, if it chips out, it's too hard; if it deforms permanently, it's too soft.

--nathan
Click to expand...

Yes this is what I mean.
Another test is a performance test. Simply sharpen it up and take it out back and hack a couple 2by4's in half and see if the edge is bent or chipped. Adjust your tempering accordingly.
 
Thanks for the replies. I had heard of the brass rod test but never really understood how it was done. After Googling it, it seems like a decent test to tell you if you're in the ballpark, although it leaves a lot of performance factors uncharted.
I have been operating under the idea that if a blade can carve the corner off a bar of mild steel without the edge chipping, bending or blunting drastically, then it will probably survive most users, but I have never really heard from other makers how they pass/fail a blade, without having real testing equipment.
 
Justin King said:
I have been operating under the idea that if a blade can carve the corner off a bar of mild steel without the edge chipping, bending or blunting drastically, then it will probably survive most users,
Click to expand...

That is one of my favorite ones for impressing people. again depending on edge geometry it doesn't "really" tell you anything.

fun to do though
 
one of the biggest problems with any edge test is that the results can be drastically influenced via edge geometry.

I could taken a chunk of mild bar straight from home depot, put an edge one it and cut a 2x4 without hurting the edge. but that edge wouldn't cut a 1" hemp rope.

the basic point being that any one edge test done by itself can be VERY misleading.

at a minimum I will cut some dried bamboo, shave some MDF, slice some paper, slice some leather, and usually shave a little arm hair.

occasionally I decide to get medieval on a blade just to see what it can do.

thats when I start shaving mild steel, battoning through preasure treated 4x4s (across grain) and other abuses
 
I substituted a piece of red oak handrail (1-1/4" x 2-1/4" oval section) for a 2x4, clamped it in my large vice and hacked through it with a blade I am working on. The edge was dulled slightly and had a few tiny ripples at the very edge which were almost invisible without a magnifying glass , but no sign of chipping or rolling over. The edge was still what I would call serviceable afterwards, and was fully restored within a few minutes on a fine diamond stone.
The blade in question is 8" long, 1-3/8" wide, .210 thick at the spine and is flat-ground all the way to the spine, with the edge ground to .014 to .012 before sharpening, and was shaving sharp before starting the test. The blade had already passed the brass rod test.
For the sake of objectivity I will omit the blade steel for the moment.
Anyone care to offer an opinion on the test or the results?
 
Its hard to say how hard the oak was and how far you wacked into it. I default to the standard ABS test and hack 2 twobyfours in half and it needs to have no damage whatsoever including ripples, nicks or dulling. It should still shave arm hair in the area you were chopping.
 
Justin King said:
I substituted a piece of red oak handrail (1-1/4" x 2-1/4" oval section) for a 2x4, clamped it in my large vice and hacked through it with a blade I am working on. The edge was dulled slightly and had a few tiny ripples at the very edge which were almost invisible without a magnifying glass , but no sign of chipping or rolling over. The edge was still what I would call serviceable afterwards, and was fully restored within a few minutes on a fine diamond stone.
The blade in question is 8" long, 1-3/8" wide, .210 thick at the spine and is flat-ground all the way to the spine, with the edge ground to .014 to .012 before sharpening, and was shaving sharp before starting the test. The blade had already passed the brass rod test.
For the sake of objectivity I will omit the blade steel for the moment.
Anyone care to offer an opinion on the test or the results?
Click to expand...


Without any more information I would say that ripples (or at least what I think of when I say "ripples") are a sign of a less than properly hardened edge. (too soft, I would think)

but I couldn't really tell ya without messin around with it myself.
 
I would say, the results from chopping 2X4's in half will tell little. I would have to think that might depend largely on the size and weight of the blade being tested, and the type of steel. Two blades of the same size and weight, one being D2, the other 1060, which would you bet on?
 
The blade I used on the piece of oak is 1075 quenched in Brownell's Tough Quench and tempered at 450F for 2 hours. I made this piece mostly to evaluate the design, 1075 was what I had on hand in the right size and would not have been my first choice for this type of blade. I am going to do one with O-1 and another with Cru Forge V and give them the same test.

I used red oak because in my experience it is much more consitent in hardness than structural 2x lumber. I always wonder when someone mentions hacking through a 2x4 to test a blade what species of wood it was? Doug fir is considerably harder than hem fir. An old-growth piece of doug fir vs. a piece of kiln dried hem fir is not an even comparison by any means. Depending on where the 2x4 came from, it could be any of several species and have moisture content anywhere from 12%-90%. Does the test count if you cut through a knot? If the board is so green it spits at you when you hit it with a hammer?

Red oak lumber here is kiln dried, relatively clear of knots, consitent in hardness and on average is probably twice as hard as doug fir and three or four times as hard as hem fir, so should provide a relatively consitent test medium and one that is fairly demanding. It may be worth noting that carbide-tipped cutting tools dull much more quickly working oak than fir or other structural lumber species.

I do appreciate the replies, it helps to have some input. I am trying to develop a testing regimen that is fairly consistent and gives me a good comparison tool.
 
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