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 Post subject: Machine sharpened knife is sharper than my others
PostPosted: Mon Feb 10, 2014 8:55 pm 

Joined: Tue Jan 21, 2014 7:00 pm
Posts: 27
Hey all,

I've encountered something that's a bit surprising to me. I took a cheapo Japanese knife (Sekizo, 200 mm gyuto) in to Sur La Table just to see what the quality of their knife sharpening is. They used a Chef's Choice machine on it and ground the bejesus out of it. But the blade came out sharp. In fact, it seems to be sharper than my Tojiro DP 210 gyuto, which was hand sharpened by Precision Knife Sharpening, nearby in Alexandria, VA.

Both knives will shave arm hair; the Tojiro does it more easily. But the Sekizo seems to cut more easily, especially with soft squishy food. Under a 30x jeweler's loupe, one can see and feel a burr on the Sekizo--I guess it's also called a wire edge--and grinding furrows all along the edge from the relatively rough grinding wheel, whereas the Tojiro has a smooth clean edge.

The only thing I can think of is, could it be that that burr makes the knife 'toothy', and it's the toothiness that's allowing it to cut more easily?


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Mon Feb 10, 2014 9:33 pm 

Joined: Fri Aug 03, 2012 10:01 pm
Posts: 210
Sounds like the machine, although removing unnecessary steel, did a better job of removing the burr than the professionals. A remaining burr on a finished edge is a negative factor either way you slice it (pun intended), and technically speaking, if your edge has a burr, it's not finished. A burr or wire edge can still shave hair, will most likely feel rougher when cutting and will most certainly cause the edge to fail under use. Successfully removing a burr when freehand sharpening does require some fineness/technique.

If you haven't already, consider getting a set of stones and learning the craft.


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Mon Feb 10, 2014 9:47 pm 

Joined: Thu May 24, 2012 6:20 am
Posts: 1841
Toothiness can help with some foods, especially foods with a waxy skin like a tomato. But the edge you are describing sound like a low quality edge to me. I expect that the burr will break off quickly and the knife will be just plain dull.


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Mon Feb 10, 2014 9:52 pm 

Joined: Thu Jan 02, 2014 6:00 am
Posts: 676
If you have a similar machine my work does it's actually putting a hollow ground edge on the blade.

They are very sharp to begin with but like others have stated, they get dull fast. This leads the user to grind the living hell out of their knife decreasing the life.

Sure the toothy edge might be easier to puncture and start the cut, but by no means is it a better edge.


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Mon Feb 10, 2014 11:12 pm 

Joined: Tue Jan 21, 2014 7:00 pm
Posts: 27
"Sounds like the machine, although removing unnecessary steel, did a better job of removing the burr than the professionals."

no. as i said, the machine-sharpened knife has the burr. my tojiro, which was hand sharpened by a professional has fine edge, no burr, no grind marks to be seen with a 30x jeweller's loupe.

"consider getting a set of stones and learning the craft."

i have a 1000/6000 king stone. i can get a knife sharp but not shaving sharp. that's going to take a lot more practice than i have the inclination for. and i don't use my knives that much (even though i love it when i do :D ). i've only had to get the tojiro sharpened once ever two years or so b/c i'm very careful with how i use it and i have very soft cutting boards.

"Toothiness can help with some foods, especially foods with a waxy skin like a tomato. But the edge you are describing sound like a low quality edge to me. I expect that the burr will break off quickly and the knife will be just plain dull."

"Sure the toothy edge might be easier to puncture and start the cut, but by no means is it a better edge."

thanks for your posts. yeah, that's what i've suspected. it's like a miniature serrated edge. so, as you've said, the cut starts faster than with the clean-edged tojiro.

but it's a real pleasure to cut with that much ease, especially with squishy foods. i don't mean to start a big controversy, but i'm going to hazard a comment because it is what i think might be true: assuming what i've got here is a toothy burr, the burr might last a lot longer in my hands than people would expect. i only use the knife for relatively soft foods on a soft (poplar) cutting board. i had it sharpened 2 1/2 months ago and it's still going strong.

again, thanks to everyone who took the time to post. you've confirmed my suspicions that i've just got a toothy edge.


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Mon Feb 10, 2014 11:53 pm 

Joined: Sun Aug 11, 2013 11:00 pm
Posts: 37
The performance you are describing seems like the difference between a very well apexed edge that is rough, versus a decently well apexed edge that is polished. That is, the machine sharpened edge has grind marks in it and the edge is not refined and polished like a razor would be, while the other blade is very smooth on the sides and may or may not have a very sharp edge.

A burr is a different animal and can be detected by feel affirmatively. An edge with a burr will feel sharper in one direction than the other. Do your normal thumb pad test for sharpness. Then spin the knife around 180 degrees, so the handle is now pointing away from you, and do the thumb pad test again. If it feels sharper one way than the other, it has a burr, or at least an edge "lean". if not, it probably doesn't have a burr.

I suspect both your edges are relatively burr free and you're simply seeing and experiencing the difference between "toothy" and "polished". Hard to say without more testing; I'm speculating.

Brian.


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Tue Feb 11, 2014 12:11 am 

Joined: Tue Jan 21, 2014 7:00 pm
Posts: 27
thanks, brian, for your thoughtful comments. i will take out my jeweller's loop again and try to scrutinize it more closely. i'm pretty sure there's a burr on machine-sharpened knife b/c i did the thumb pad test and found it rougher on one side than the other, but i'll do it again. i've felt burrs multiple times in the course of sharpening and this one didn't feel the same. as you said, it could be that it has a 'lean' rather than a burr.


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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Tue Feb 11, 2014 4:36 pm 
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Joined: Wed Aug 07, 2013 12:44 am
Posts: 1034
In my experience the Chef Sharp machine is not a very good sharpening apparatus. It tears the blade to pieces and gives you in return a blade that is usably sharp for about 5 minutes.

The difference could be just what was suggested. A burr was left on your Tojiro.

Sometimes though, a "toothy" edge does treat soft ingredients better, but this is also, in my experience, not always true. A dull serrated house knife will never, ever slice tomatoes as thin or easily as my sharp non serrated knives. That, however, kind of goes without saying.

Keep at your sharpening, and don't give up. The savings is a great perk but the comfort level it will give you with your knives is the real reward.

As for a reliable de-burring procedure, try felt or soft wood, like cork, this will break off most burrs without the added work on the stones.



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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Wed Feb 12, 2014 3:12 am 
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Joined: Tue Oct 30, 2012 12:20 am
Posts: 628
I used to strop my knives to a razor finish on a charged strop, but not anymore.
Razors are meant to shave with, not slice tomato's and red peppers.

Now I love the fine, toothy edge I get off my 8k (coticule), and it lasts longer too.

Image

Aogami edge



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 Post subject: Re: Machine sharpened knife is sharper than my others
PostPosted: Thu Feb 13, 2014 2:21 am 

Joined: Tue Jan 21, 2014 7:00 pm
Posts: 27
i took a look at these knives under my 30x jeweler's loupe again. the tojiro has the polished edge you were talking about. the machine-sharpened sekizo shows grind marks and i'm pretty sure that's a wire edge. i don't have the ability to photograph it, unfortunately. but i can attest there's a very bright line right along the edge on one side and it's not there on the other side. so i think we're talking about a burr, not a 'lean'. the burr is finer and more subtle than the burrs i get when i sharpen, so that threw me.

so, i think i've just got a very toothy knife and that's what makes it cut more easily through tomatoes, kiwi skins and apple skins.

"I used to strop my knives to a razor finish on a charged strop, but not anymore. Razors are meant to shave with, not slice tomatoes and red peppers. Now I love the fine, toothy edge I get off my 8k (coticule), and it lasts longer too."

yeah, interesting point. the professional sharpening i got with the tojiro may have done an impressive job for shaving arm hair, but that's not what the knife is used for...


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