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Author Topic: "How Do You Test Your Knives?"  (Read 4350 times)
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ChrisAnders
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« on: June 07, 2015, 09:19:06 PM »

I've seen this question in response to questions about various things regarding knife performance.  What is the correct answer?    

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John Silveira
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« Reply #1 on: November 24, 2015, 11:46:06 PM »

i saw this post a few days ago - then it looked like it disappeared !

that's a good question. Lots of different testing techniques.

rope cutting - battoning - flex testing - brass rod testing - on and on. I'm not so sophisticated when it comes to testing - haven't done much.

i haven't said anything worth repeating here. LOL
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Ed Fowler
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« Reply #2 on: November 25, 2015, 10:08:35 AM »

I strongly feel this is a question that should be asked of every knife maker for their methods of testing reveal the true essence of their blades. I could get on my soap box, but will ask that all who are interested start by discussing what they feel are essential aspects of the blades they develop.
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Joe Calton
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« Reply #3 on: November 25, 2015, 04:37:11 PM »

I don't know that there is a "correct" answer, but as long as it is honest, then its correct enough for me.

I am brutal on knives. both in my shop testing and in my everyday use of them. I also really enjoy testing on video, and posting it on my youtube channel, not so much as a advertising gimmick, but so that anyone who buys a certain class of my knives can see what they can expect out of that class. plus doing the testing on video, I can go back and watch it again and again and from often a different angle than what I saw when I tested it.

I am usually after good to great performance for that class of knife. as in I would not make a chefs knife indestructible, as it would then suck as a chefs knife. and a hard use knife would not cut as efficiently as a paring knife as it would not be very indestructible.

I guess my main goal in testing is to see what they will do, and be able to predict the level of performance in whatever class, as well as predict the kind, and level of damage under different kinds of abuse so that I can relate that to the person who buys and uses it so they can get the most out of their hard earned dollar.
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Ed Fowler
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« Reply #4 on: November 25, 2015, 06:00:56 PM »

This is the first test I give all my blades. The knife is hardened and tempered and ground to an X22 grit, the tip is sharp and I jam it into the base of my Burr King then check the tip for any deformation. If it has deformed I re-rind it and test again until there is no deformation. If the tip does not pass this test the blade will be re-hardened or go to my experimental blades.



I like the tip on my field knives to be sharp, it must bite into the steel and be able to engrave a line in mild steel without skipping or deforming. You can either try to push the blade to engrave or it is easier to tap on the tang with a light hammer to drive the tip into the test mild steel. Simply jamming the tip into the mild steel with my hand is easiest, the harder you jam the tip into the steel the better your test.

After my final work on the knife it is sharpened a final time then a quick test of the tip by piercing a piece of paper held a 15 degree angle, this is an indicator of tip geometry and that I have removed the final burr off of the spine of the blade.
« Last Edit: November 26, 2015, 09:17:31 AM by Ed Fowler » Logged

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« Reply #5 on: November 26, 2015, 04:31:36 PM »

Another test for tip strength with extra emphasis on tip geometry. The colors are off, but you can see me engraving the side of a double jack hammer using the tip of the same blade and a light hammer striking the end of the tang. It does not take much to scratch a piece of steel, but to engrave a line provides the maker an opportunity to explore the nature of the knife he is making.



Just fun stuff, that provides an opportunity for greater knowledge about the tip of the knife. All a tip needs to do get you into your work, it only has to work for a little while when compared to the rest of the blade, but when a tip fails you have a lot more work to do.

Just play with it, increase the angle into the mild steel for deeper cuts or lighten it for more shallow cuts.

After you have engraved you can easily evaluate the quality of the tip of the knife, it should still be capable of penetrating into your work. Here you see me poking the tip of the blade into my finger prints, it wants to dig into them.
Shooting the photo I let more pressure on my finger than was actually necessary.

Caution!! Knives can bite you!!

« Last Edit: November 28, 2015, 04:26:13 PM by Ed Fowler » Logged

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« Reply #6 on: November 27, 2015, 11:06:31 AM »

Does anyone "flex" their blades  (i.e. 20-30 degrees) and then check for a return to straight?
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Ed Fowler
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« Reply #7 on: November 28, 2015, 09:18:05 AM »

Good question!

When performing the first 90 degree flex with a test blade is the time to check for return to straight. Presently I always do my flex tests using a torque wrench attached to the blade. Progressively add more force to the blade, watching the torque wrench, flex the blade 5 degrees and check for return to straight, then go 10 degrees and see if it will return to straight, continue to increase the  amount of flex to the blade, until it no longer returns to straight.

You will learn a lot about your heat treat, the influence of the geometry of the blade on your bend tests. When ever I flex a blade like this I continue to test the blade to destruction instead of selling a test blade to a client.


The object of testing is to obtain all the information you can from each individual test. I wish I would have used the torque wrench from the beginning of my testing, I simply did not think of it and merely recorded my subjective observation of force needed to bend the blade.
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« Reply #8 on: November 28, 2015, 09:59:17 AM »

Thanks Ed!  I need to review Mark's video taken at your place = I think he had the same approach
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Ed Fowler
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« Reply #9 on: November 28, 2015, 05:29:11 PM »

I just added a third photo and more description on how we test our tips. There is nothing simple about the tip of a knife, we are only limited in design by our experience using knives. This discussion was all about tips for a knife made for use in the field where performance really counts.
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« Reply #10 on: November 29, 2015, 12:14:27 PM »

Don't be bashful, if you have any comments about the first discussion about testing the tip of the knife you are invited to comment.
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John Silveira
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« Reply #11 on: November 29, 2015, 06:53:28 PM »

well -
i think i'm a little awestruck with the engraving with the tip aspect of testing ! Who came up with that idea ?

A friend came to me the other day with a pocket knife of his with a tiny bit of the tip broken off. Have no idea what kind of steel the blade is ( possibly one of the new powdered steels ).

Ed - curious: The blade in your photo says it's from 6" round stock. Of course i'm wishing i had some billets that were from 6" round stock . Maybe someday. But i'm wondering if you found any difference in your tip testing when you stopped using 6" round stock and went to smaller stock ? I've inquired about getting some flat stock from you that started as 6" round stock and i was told it's no longer available ( It's probably your private stash now ).

But the question is did less diameter round stock billets degrade that tip strength during your engraving testing.

And maybe you have time for one more question: You recently posted a photo of the blade you said was a modified price grind that was a reverse taper - i mentioned it looked like it had quite a bit of meat in the front section - then you explained why - Wondered how good that reverse taper grind Cut ! Do you still consider that grind one that you'd use ? I started my blade smithing with flat grinding and they always got pretty sharp - i'm still getting used to convex grinding and trying to get comfortable with the best geometry involved. ( Haven't refined convex grinds to the point where i feel the blade has the best of both worlds ( strength and sharpness )
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Ed Fowler
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« Reply #12 on: November 29, 2015, 07:57:24 PM »

I have no idea who used a knife tip to engrave mild steel first, I just started doing it about 30 years ago. I have used bone, but the tip penetrates too fast and the sides of the blade to most of the work. I wanted to test the very point of the tip and the mild steel proved to provide me with the best information. The harder the steel you are engraving, the smaller the area of the tip you are actually testing. You will see ads of folks jamming their blades through steel plate, this is no test of the tip, but again tests the sides of the blade, all the tip does is get you into your work and that is the aspect I wanted to test.

Using the tip of the blade to engrave mild steel is not as big a deal as it looks, while it is a valid test, and a poor tip will not stand up, you are only testing .0001 inches of the blade.

Blades that I have forged from 3" and even 1" round stock have also performed very well I feel that you could use any round stock from 1" up and if forged and heat treated right will provide knives that can be called high endurance performance blades. I was showing a new maker an old test blade, we were looking at the tear from the tip to the soft back and could see five separate fracture plains that matched 5 transition zones on the side of the etched blade. I thought that it was 52100 and he simply read what we had written on the blade at the time of the test and said "this is JD 5160". That blade was definitely a high performer. Great steel will perform when you nourish it.

What I call the Modified Price Grind is a complex grind and can provide a slicing edge as well as a chopping edge, it is all up to you. The beauty of it is that it is a challenge and you have the opportunity to develop a real relationship with a blade.
I was worked up and etched a reverse taper Price grind on a 5 " blade two days ago. Finished up etching the blade about 10.00 PM and went to bed. That night in my dreams the blade was swimming before my eyes, the distal third would expand up like a blow fish and swim slower, then shrink and really move, changing shape, twisting and turning, all I could think was WOW.  I woke up about 3AM, got up and walked out to the shop and took the work scabbard off to look at her just because.

I find it impossible to get bored when developing a price grind.

If you experiment with variations of the convex grind and test for performance you will find that the convex grind is a true wonder to work with. Don't be bashful about sharing your thoughts and thanks for the questions.

 

Next spring I plan on working down some more 6" round stock. A new maker is looking to spend the next year on the Willow Bow and he is a good hand, he is a mechanic supreme and I look forward to getting my Beaudry running as  soon as it warms up.
« Last Edit: November 30, 2015, 11:37:35 AM by Ed Fowler » Logged

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John Silveira
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« Reply #13 on: December 01, 2015, 11:43:48 AM »

This is the first test I give all my blades. The knife is hardened and tempered and ground to an X22 grit, the tip is sharp and I jam it into the base of my Burr King then check the tip for any deformation. If it has deformed I re-rind it and test again until there is no deformation. If the tip does not pass this test the blade will be re-hardened or go to my experimental blades.



I like the tip on my field knives to be sharp, it must bite into the steel and be able to engrave a line in mild steel without skipping or deforming. You can either try to push the blade to engrave or it is easier to tap on the tang with a light hammer to drive the tip into the test mild steel. Simply jamming the tip into the mild steel with my hand is easiest, the harder you jam the tip into the steel the better your test.

After my final work on the knife it is sharpened a final time then a quick test of the tip by piercing a piece of paper held a 15 degree angle, this is an indicator of tip geometry and that I have removed the final burr off of the spine of the blade.


So in the top sentence you wrote you mention if the tip doesn't pass the "Jam" test that you re-grind and test again till no deformation ...

So are you re-grinding simply to get to a thicker tip geometry that won't deform ?  you're not re-tempering or re-hardening you're just re-shaping the tip till it has the strength you're looking for ...  

Then - if the blade didn't pass the test i'm assuming the heat treat didn't work out right ? Bad steel for some reason ? Maybe the tip overheated a touch and grain growth occurred ?

i do understand the modified price grind you mention - it's thinner closer to the ricasso along the edge and grind so it's going to be a sharper/easier to sharpen and better cutting edge there - then as you move forward on the blade with the grind it's thicker for better toughness of the edge for chopping type use out at the further toward the tip part of the blade where most chopping happens ( my quick explanation ).....

Oh !  by the way - looks like you tip tested a knife or two by the looks of that Burr King base - ha ha !
« Last Edit: December 01, 2015, 06:10:07 PM by John Silveira » Logged
John Silveira
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« Reply #14 on: December 01, 2015, 06:34:37 PM »

I just added a third photo and more description on how we test our tips. There is nothing simple about the tip of a knife, we are only limited in design by our experience using knives. This discussion was all about tips for a knife made for use in the field where performance really counts.


Where is the 3rd photo ? am i missing something ?
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