Kitchen knives blunt super quickly

Hey guys,

after making some leaps forward in terms of sharpening, I'm experiencing something very strange.
I mainly focused on kitchen chef knives in the last few days. I got 1 in x50crmov15 ~56HRC and 1 in Niolox 61HRC. The problem I'm having is that even after cutting 2 carrots I can already see reflecting parts on the edge.
The sharpeness after the stones allowed me to pushcut newspapaer cross-grain easily and cut curves into the newspaper. Hair was caught above skin. The finishing and deburring stone was a Spyderco Medium. The edge bevels were 15° with a 17° microbevel. Second try was 17° bevel with 19° microbevel. The problem was more or less the same.
I'm starting to think my birch cutting board is causing the problems, because even after intentionally hitting the edge of the cutting board with the Niolox knife, I could see no edge damage at all. But if I slice the knife over the cutting board 50 times with moderate pressure, the edge shows significant damage.
Any ideas? Not deburred properly? Abrasives in the cutting board? Wrong cutting technique?



Edited 2 time(s). Last edit at 12/14/2020 07:24PM by sai.

There could be a problem with the heat treatment or other processing stages on the knives. It’s hard to know though, so just to be clear I’m guessing and not claiming that I know they’re burnt or something.

I’ve been using a Spyderco K08 Santoku (MBS-26 Steel, polypropylene handle) for 9 months, cutting on a walnut wood board, and I’ve never seen damage from the work like what you’re describing. The only time I’ve seen light reflecting is on an accidental contact with a hard object, or when the edge actually collapsed in several places when cutting through tough fish bones. And I’m using an edge angle and thickness that’s lower than what you’re describing as well, about 10 DPS with either a 15 DPS microbevel or no microbevel at all, just a 10 DPS edge off the Naniwa 1,000.

My suspicion is that either the knives are burnt, or you’ve not actually de-burred them and the burr breaks off or collapses when you start cutting.

Let me give some additional information, because this knife has turned into a project for me anyway. I'm mainly focusing on the Niolox knife now. It has already consumed so much time... lol

The knife maker is pretty known in germany and pretty much exclusively uses this steel (Niolox) for the last 10 years probably. So I don't think the steel has a problem.

He does powergrind his knives but watercooled. Despite that I blunted it probably 5 times, so there should be fresh steel at the edge by now.

The damage I'm seeing also makes me think that it's a burr that's just collapsing with the first use. But I really don't know how to detect it, since it must be so super small. All methods known to me detect absolutely no burr.

What else can I do? I set the edge on the Chosera 1000 and microbevel with ultra light strokes on the Spyderco medium. The edge looks super consistent under the pocket microscope and when I look at the edge from adove I see no reflecting light even with the microscope.

I did notice one strange thing though. When cutting newspaper slow to medium-paced cuts work exceptionally well, but doing a fast motion the edge sometimes (!) catches. Is that maybe an indicator of a very fragile burr bending under the pressure of the faster cut, but doing well on the slower cuts because it's perfectly straight with no real load?



Edited 1 time(s). Last edit at 12/14/2020 09:50PM by sai.

In that case I’m not really sure, I don’t think I know enough to be able to really help much. Unfortunately.

Sounds like you have the infamous, hard to detect, hard to get rid off, micro-burr. Try running the edge through a piece of wood or cork, and then doing 5 passes per side, light, forward leading, on the Spyderco Medium. Try stropping if that doen't work, with some kind of abrasive on leather, newsprint, copy paper, or cardboard.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Thanks for the input. I'm also thinking of something like a wire-edge.
In fact I tried stropping on loaded leather, newspaper and cardboard by now and drawing the edge thorugh softwood. Cork is the last thing I didn't try. Oh and I also tried high angle deburring passes at like 30°.
Additionally I'll try the strop on my TSProf. This gives me maximum angle control and I can't screw up anything while stropping.
If all of this doesn't work, I'll probably send the knife in to getit sharpened by the maufacturer and do the same edge tests I did before.

Some new info here. I was searching around for a knive which still had a factory edge on it and found my PM2 in S30V.
Took one of my testing carrots out of the fridge and startet cutting it up. Surprise there were reflecting parts on the edge. So either my cutting board is loaded with abrasives or I'm too stupid to cut up vegetables. I'm leaning towards the second.

sai,
Is there anyway you can take some pictures of what is going on with the edges? It would really help to try and figure out what is going on.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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I'm afraid my current pocket microscope won't really deliver any insight. But I'm getting a new one for christmas. Maybe this will help to take some decent pictures.

sai,
I don't need microscopic images, just regular ones are fine. When you were saying you saw damage, was this viewed from a microscope or the naked eye?

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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There are so many things that could be going on. so it is very hard to judge. especially without seeing some pictures of the knife and its cross section to get an idea of how it looks, and what the level of damage is. is it blunting and reflecting light across the entire edge?
is the damage worse than if you use the knife to cut a steak or something on a ceramic plate?

if you think its the sharpening, then you need to take the process down and simplify it. Look at Cliffs 3 step video and try a very basic sharpening.
if the steel and ht is decent 55rc plus, then if the apex geometry and everything is fine, then you should have no issues cutting plastic bottles, cutting bamboo skewers etc etc..

i suggest that you stop cutting on the board for a moment and test the knife cutting a range of materials that you know should pass with flying colors and not dull the knife and see if the knife is ok.. once a common benchmark is found with others using that type of testing, start introducing your cutting board back into the mix. what brand? how is it made? how was it bonded? is there sand any sort of roughness from bad glueing or filler etc.

get a cheap polyprop board and test on that. if its fine on that, and not fine on the other board. get rid of the other board, or sand the top down and try again..

to many variables involved.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen

Picture this. I just took my stress test one step further. I chopped small chips of wood out of a piece of spruce. Then 50 forceful slices through the wood, digging in deep.
Inspected the edge afterwards, nothing. Shaves like mad and slices newsprint just like before.
If my girlfriend didn't witness all my testing, I would probably think I'm slowly going insane.
I'm ditching the cutting board right now. Then the last variable left is my cutting technique. Although I can't imagine how I could be any rougher to the knife than chopping wood...lol.
I baby my knives.
At least I got a big smile on my face now that my edge came clean off the stone, as I really couldn't detect any leftover burr.



Edited 3 time(s). Last edit at 12/16/2020 06:12PM by sai.

What cKc said. Try that.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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The only way i could imagine your technique causing the issue on that type of board if its not dulling otherwise is if the edge is biting into the board and you are laterally twisting on the cut and the board binder is bad.

its sounding like the board is the issue without any other specific information

"Then 50 forceful slices through the wood, digging in deep."

these cuts dont really test the durability in the same way as the edge is supported and the wood is soft so uther than chipping or folding from lateral stress we'd expect you do be able to do a lot of cutting in wood with a knife within the constraints of the knifes geometry.

often for testing a kitchen knife edge i will just take it and chop into the board a couple of hundred times with reasonable force as though i wanted to chop a chicken leg in half without the chicken in the way. this is putting the same type of small stress on the edge as if you were slamming a cucumber fast etc.

like i am doing in this video at the 20 second mark for 40 seconds or so.. if the knife dulls doing that then your edge is too frail, or the board is hurting the edge




----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen

quote: "But if I slice the knife over the cutting board 50 times with moderate pressure, the edge shows significant damage."

Your board is loaded with very fine silicate/grit. Pushcutting/chopping on this board will dull too but at much slower rate.

As for sometime catches when fast slicing newsprint/phonebook - probably snagged by high feed rate against a few carbide burrs or carbide divots.

Wash the carrots.

Thanks for all the input guys.

New day, new testing. So as you suggested cKc, I cut up a plastic bottle into dozens of small pieces and the edge wasn't affected at all. I chopped the cutting board like in your video, no impact on the edge.
Now back into the kitchen, I took my girlfriend's cheap plastic cutting board and diced a pepper and there we go, I got edge damage again.
So I guess all there is left now is my cutting technique? Even though I did every slice very carefully, no excessive force or anything. I guess I'm twisting (?) the knive without even recognizing it, even when having an eye on it.

@me2 the carrots were always peeled in order to avoid getting dirt on my cutting surfaces.

P.S.: Alright I just confirmed it. I did a short slice, then intentionally twisted the knife a bit and there we go. The damage looks like what I'm seeing after slicing up carrots, peppers, etc.



Edited 2 time(s). Last edit at 12/17/2020 09:35PM by sai.

Good, you identified cause of the problem.

Out of curiosity, I pull slice carrot and twist/pry 45+ degrees sideway to detach thin cut carrot piece from blade. After 50 slices+pries, this 63rc niolox edge (12 dps, 15 dps micro) would still quietly slice phonebook paper.

Are you talking about roll or yaw? I guess when you say pry, you mean leaning the knife clockwise (if you're right handed) or counter-clockwise (if you're left handed)?
The movement I'm doing seems to be called "board walking", at least that's what I read on some kitchen knife forum. People report chipped edges by doing this, since my knife is only hardened at 61 it seems to have plenty toughness left to roll instead of chipping. I guess?



Edited 1 time(s). Last edit at 12/18/2020 07:15AM by sai.

Reset the bevel again with diamonds in a guided system. Coarse-Medium-Fine. 2 strokes with a SiC loaded leather strop.
Went to the a cherry-wood cutting board, did 30 dry chop slices, paying attention to a straight cutting line. And I got edge damage. The reflecting area is noticably blunted and catches on newspaper. The rest of the edge is fine.
Now I cut up cardboard into 60 pieces each 4 inches long. The damaged area is pretty much unaffected but the sharp part is now only scrape shaving. Is this an expected result in terms of cardboard cutting performance for a clean 15° edge?

Your 15dps 61rc niolox seems a little prone to edge damages ...

Currently I am making many niolox knives, so here is a new test video:

Niolox 63rc 13dps cut bamboo and pork bone Tests
[youtu.be]

*note: 15dps is 54% stronger than 13dps (volume strength = power(15/13,3)

closeup of edge afterward: [i.imgur.com]

Thanks for this! Now I got a rough idea of what I can expect from my edge.

I put on a 10° relief bevel (tertiary) on the knife now in hope that it reduces cutting forces when cutting harder vegetables like carrots, etc.
I'm going to use it over the holidays now and inspect the edge afterwards. But I can already see the tip area has two shiny parts and this part never gets any impacts.