How do you sharpen a very dull knife?

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josemartinlopez

josemartinlopez

我會買所有的獨角獸
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Stupid question, but how do you sharpen a completely dull knife? No chips but just completely dull and unable to cut paper. Should you go to a much lower grit? Is it different if you have a softer Western steel?
 
I start any sharpening by thinning behind the edge, at the lowest possible angle, and raise the spine little by little until the very edge has been reached. If a knife has been severely neglected it often is very fat behind the edge as well. Just sharpening the edge without thinning won't make much sense. The thickness behind the edge will force the user to apply much pressure. So the contact with the board will be violent and no edge will hold.
To get an idea of the thickness behind the edge to aim for with a chef's knife: 0.2mm at the top of the bevel, 0.5mm at 5mm from there, and 1mm at 1cm from the edge.
 
Although I understand what Benuser says, to get a dull edge sharp there is no need to go to a much lower grid. I think you can start with anything let's say from 500 to 1K. Things will just go a but quicker so I would start at 500 and work from there.
 
Found a very dull knife in one of my old tool boxes recently. Been in there since about 1985, I think. Carbon steel, Parker "Eagle" brand, made in Japan, back before that meant something good to most Americans.

It had been badly abused. Used to clean some squirrels and forgotten, dirty outdoors in the rain for a few weeks. Corroded, ugly, used as a garden knife/planting trowel after that by someone who didn't think it could be fixed. I think that blue/black stuff remaining around the logo is PAINT, not bluing.

500 grit Shapton glass to get past the extremely rounded edge from being used as a garden trowel, a 1,000 grit diamond water stone and a 3,000 grit stone. Stropped on denim with a little bit of Turtle Wax scratch remover/metal polish.

Can shave arm hair, slices paper easily and it will cut vegetables, rope or what have you pretty well now. Whatever Parker's Japanese makers used was a pretty decent cutlery steel-

I'm tempted to reshape the blunted tip, strip the remaining paint, blend the pitting, even out the bevels, polish and try to force a patina on it.

20200725_175805.jpg


20200725_181900.jpg
 
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josemartinlopez said:
Stupid question, but how do you sharpen a completely dull knife? No chips but just completely dull and unable to cut paper. Should you go to a much lower grit? Is it different if you have a softer Western steel?
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That depends on how badly damaged or rolled over the edges are. In a worst case scenario, I've even used an axe-file to completely get rid of the old edge and start fresh on stones. There's little point of using stones when edges are completely destroyed.

You also have to weigh the value of the knife against your cost (time/stone-wear/etc) Is the knife even worth repairing?
 
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josemartinlopez said:
Stupid question, but how do you sharpen a completely dull knife? No chips but just completely dull and unable to cut paper. Should you go to a much lower grit? Is it different if you have a softer Western steel?
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Depends partly on how confident a sharpener you are. If you are confident, you will not want to **** around forever on a medium grit stone, so you’ll use something coarse, like 300-500. It’s just a tradeoff. You’re trying to remove as little metal and as little stone as possible, while taking as little of your precious time as possible, while getting a good edge in the end. Only you can decide how best to optimize in this situation.

But just go try it...
 
A fast way of performing both some thinning and restoring an edge is the use of coarse automotive sandpaper — edge trailing only to avoid overgrinding. Use a hard rubber or soft wooden backing.
 
I use atoma diamond plates. That is all i use on the western knives i am asked to sharpen. My son brought his Whustof santuko yesterday the only reason it cut was so many chips it was almost serrated. Or i willl get the tormek out with black silicon carbide wheel
 
Chips? Really? I would rather expect a broken wire edge, which may indeed look as if micro-chipping occurred. Always expected Krupp's 4116 to resist chipping and roll-over instead. So far the only soft stainless I knew to chip was Global's Chomova.
 
Benuser said:
Chips? Really? I would rather expect a broken wire edge, which may indeed look as if micro-chipping occurred. Always expected Krupp's 4116 to resist chipping and roll-over instead. So far the only soft stainless I knew to chip was Global's Chomova.
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Never underestimate the ability of careless line cooks.
 
Kawa said:
Today:
Friend of wife: "So, you sharpen knives I hear... Can you take this one with you?"

View attachment 88510

Me: ".. No. I don't do breadknives"


Damnit... Somehow it still landed in my hands and home
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That's nothing compared to some of the knives that I recently sharpened. 16 knives that my buddy's wife bought at a thrift store for $0.50- $1. She thought they were a "real bargain" and kept them stored unprotected in a large wide-mouth jar. I have NEVER in my entire life seen such badly rolled over edges,,,, I never imagined it was even possible to get them in such poor condition. All of the blades were severely rolled over, from heel to tip. On close inspection, rather than being one continuous rolled edge,,, it was actually hundreds of smaller rolled edge sections, joined to form one continuous roll-over along the entire length of each blade; and a lot of mushroomed edges too. There was only one knife in the entire bunch that was half decent quality, and the others probably cost under $5. new. I didn't want to disapoint her, and after some head-scratching, I decided to do them in a Chef's-Choice Trizor knife sharpener, and she's bowled over by how well she thinks they now cut. Phewww!!! I can hear my stones whispering " we're saaaaaaaved"
 
Noodle Soup said:
Not really that bad from some I've seen. I say an extra 10 minutes on a 300-400 grit stone.
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I wasn't entirely serious. Have all the stuff I need. But don't like soft stainless. Globals are annoying, but the most terrible were Kai Wasabi, with huge clustered carbides. Extremely wear resistant, AND unstable.
 
ian said:
I have it on good authority that if a knife is really dull, you can just strop it on the bottom of a coffee mug and the edge will come back.
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So the nicks get filled, the broken tips grow back as well?
Seriously, it does work very well. A bit coarse, around 600 grit. May do for an EDC.
 
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ian said:
I have it on good authority that if a knife is really dull, you can just strop it on the bottom of a coffee mug and the edge will come back.
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No,no, no,,,, you drag it from the back of a truck that's full of coffee mugs,,,,,, edge trailing of course.

There, I fix't it fer ya. :cheers:
 
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