Are there blades next to impossible to get really sharp?

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miklobe
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Are there blades next to impossible to get really sharp?

Post by miklobe »

I have two or three blades on which I cannot get a good edge. One of them in particular seems to have a steel that is impossible to sharpen. After considerable stropping in will "cut" [more like "tear") a sheet of paper into a short line, but it is far from satisfactory. Shall I give up on this or pay a professional to sharpen it? It is a cheap knife, but its steel is very frustrating to work on.
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philco
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Re: Are there blades next to impossible to get really sharp?

Post by philco »

I am far from an expert on blade steels but it has been my observation that some blades are made with such inferior quality steel that you just can't sharpen them to a satisfactory edge, or, if you manage to get them sharp, even one light use will cause the blade to dull once more. It seems that sometimes the steel is such that when you do get an edge established it just rolls over to one side and you have a dull knife once again. In a situation such as that, I don't think it matters who is trying to sharpen the knife. You simply can't make a silk purse out of a sow's ear.

Can you tell us what the knife you are having problems with is? That might help shed some light on the true source of the problem.

Phil
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Froggyedge
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Re: Are there blades next to impossible to get really sharp?

Post by Froggyedge »

Miklobe,
I've experienced the same as you. Once in a while you come across a blade that is next to impossible to sharpen.

I agree with philco. Some knives are made with such inferior steel quality that no matter what you do and how you do it, it just will not take a decent edge, or the edge will be gone after you peel an apple. Heat treating gone wrong may also be the problem.
Fortunately, blades that bad are not common even among quite inexpensive knives.
Paying a professional to sharpen those bad ones is a waste of money.

Some blades rating high on the Rockwell scale (extra hard) may be difficult to sharpen even though the steel is top quality. In those instances a professional sharpener may be a good alternative.
What do you use when sharpening your knives? Getting a really dull knife sharp with a hard Arkansas stone (or hard ceramic) takes a looong time...
When the edge is really dull or needs reprofiling, I start with a diamond hone.
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Darksev
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Re: Are there blades next to impossible to get really sharp?

Post by Darksev »

There are a number of things that make a blade difficult to sharpen. Most have been touched on, but I'll elaborate a bit (been so busy lately, I feel like I'm not participating much here anymore. gotta fix that :P).

1) Blade geometry - first and formost, this will cause a blade to be unsharpenable. If the blade is to thick, it will be unable to accept anything resembling a sharp edge without major work to knock down the shoulders of the edge. You can see this on knives very easily if you pick a good blade angle for your purposes (I like 30 and 40 degree edges, 40 for most use, 30 for REALLY sharp slicers). If you apply that edge with something with an angle guide (like an edgepro, lansky setup, or sharpmaker) you will see a HUGE edge form. You see extreme examples of this alot on older, heavily used knives where they get worn down. All that's left is a thick whack of steel, so someone has to almost re-grind the thing to give it an edge again.

2) Cheap (soft) steel - Anything hardened to a point below low 50's Rc is pretty much useless as a cutting implement (With a few crazy mad science exceptions, anything with lower than .4% carbon). While you can form a decent edge, the very first use dulls it immediately, as it's not hard enough to withstand the abrasive nature of cutting. Even something like paper can wear away microscopic bits of the edge. Even more extreme is steel that won't form an edge, it forms a burr. A burr is a super thin, floppy piece of steel attached to the edge that is formed during sharpening. think of it like a piece of tinfoil. Anyone who's worked with foil will tell you, the edges of it can be SHARP! but as it lacks any kind of supporting structure, if you try to use it as a cutting edge, it will fold over almost immediately. This is what a burr does on a knife edge.

3) insanely hard steel - Steel that is hardened past the "sweet spot" becomes brittle. Sharpening brittle steel is difficult because the act of sharpening is running an abrasive across the edge. In very brittle steels, this alone is enough to cause chipping and any edge that is formed almost immediately cracks off and breaks away, leaving a jagged "tearout" where the edge used to be. Some very new steels like ZDP-189 are extremely hard (like 64RC in some cases). Where most steels are very brittle at this point, ZDP is engineered to be "normal" at hardness that high. with non-brittle super hard steels like that, getting a good edge takes a very long time, unless your using diamond abrasives (I've heard of people having a ton of issues with ZDP and ceramic sharpeners, which are usually great on normal steels)

It sounds to me like alot of your issue has to deal with good ol' #2. I'd be willing to bet that the knives in question are a 420 series steel. Very few of those steels make for good blades (and even then, it's all down to a mastery of heat treatment. Ex: Buck does a serviceable job with 420HC)
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woseyjales
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Re: Are there blades next to impossible to get really sharp?

Post by woseyjales »

miklobe wrote:.....After considerable stropping will "tear"
a sheet of paper into a short line, but it is far from satisfactory.
It is a cheap knife, but its steel is very frustrating to work on.
Even such a sorry utensil (hate to call it a knife) has value.
You never know when you might need such a piece of !@#$%
to place in a despicable person's airport luggage. ::nod::
If you want/need a cheap knife with good edge holding ability
may want to try an Opinel #6.
Carbon blade base model about $12, stainless with bubinga handles
runs the price tag way up to $24.
Oak, walnut, olivewood versions in the middle.
Makes for a good kitchen knife too (watch your fingers!)
Only cuts three ways, long...deep....& continuous.
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redferd
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Re: Are there blades next to impossible to get really sharp?

Post by redferd »

I have had some steel that just won't sharpen no matter what I try. If I do run into a blade that won't sharpen, I use a coarse stone to get a ragged edge and make do with that. ::dang::
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Re: Are there blades next to impossible to get really sharp?

Post by jmh58 »

Have a Benchmade that is very, very hard to get a good edge. ::td:: . Dont carry that no more. :evil: . If it cant be sharpened, that it cant be carried ::shrug:: .. John
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Mossdancer
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Re: Are there blades next to impossible to get really sharp?

Post by Mossdancer »

Hi:
Darksev mentioned something nobody else has stumbled upon. I found while researching the early Gerbers and that is blade geometry. Take a knife with good steel that you can sharpen and one with the same steel that you cannot sharpen. If you can get it setup to do, place them both under a 10 power or higher loop and look at the angle or geometry of the blade and you will immediately understand(more than likely) why you cant sharpen the one. The angle will be completely different, adjust the angle of your hand or stone to proper angle and it will just make a heck of a difference. People use to throw away Gerber knives because they could not sharpen them when the angle was causing the problem.
Gerber tempered to 59-60 which some companies did but their angle on blade was and this is without checking so is subject to being corrected 23 degrees.
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knife7knut
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Re: Are there blades next to impossible to get really sharp?

Post by knife7knut »

I have a custom drop point hunter that I purchased many years ago from a knifemaker that was near impossible to sharpen by NORMAL means.It has a 1/4" thick blade of O1 tool steel hardened to RC61 that is hollow ground and then has a convex edge put on it.After a long period of moderate to severe use it needed to be re-edged.A normal stone was useless;the blade just slid across it doing nothing.I called the maker(who has since passed away)and he told me to send it back and he would re-sharpen it at no charge.
Trusting the U.S.Mail about as much as I trust a used-car salesman with slicked back hair and an evil smile,I looked for other solutions.
A friend of mine who works in a machine shop offered to do it on a rubber abrasive wheel.Came back with a shaving sharp edge(like it was when new)that has yet to be re-done.Not advisable for all applications but good for convex edges.
I use several grades of diamond stones to do most of my knives and they are well worth the investment.If there is any secret to sharpening knives,it is holding a consistent(and correct)angle while honing.I do not use any sharpening aids although I have several as I find it easier to do them free hand.As with any thing,practice definitely makes perfect.
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Aimus Moses
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Re: Are there blades next to impossible to get really sharp?

Post by Aimus Moses »

I agree with you K7K. Every knife I sharpen is free hand. I remember the fuss about the early 440C steel bladed Buck knives being hard to sharpen. It was rumored that the only way they could be sharpened was to send them back to Buck or buy Buck rocks. In my first experience with a 440C bladed Buck knife I found that they were a little harder to sharpen than 1095 carbon steel bladed knives but not a lot. They held an edge longer than the 420 steel bladed knives do in my opinion. I think the steel type and blade thickness plays a large role in sharpening a knife.

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miklobe
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Re: Are there blades next to impossible to get really sharp?

Post by miklobe »

Thanks to all who replied.

I wanted to mention that some of my sharpest knives are cheap ones from China, but that my Champs for sharpness [out of the box] are some Kershaws, mostly made in the U.S.
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