Can you ever get a knife, too sharp?

[The_Knife_Man]

Knife Man, I respect your opinion, just like I respect everybody else's on here. My point was to start honest debate.
My thoughts are that a knife can be too sharp, but then again, possibly I don't know your all's intended use?
I guess my use for a knife is purely utilitarian. I want the edge to work for me doing menial tasks and I want it to last as long as it can.

Given the proper edge angle on the right blade geometry for a particular use, I don't think you can over sharpen it. I think one can have an edge that is to thick or to thin. Depending if you want a chopper or a slicer.

Extreme example: putting a 10 degree per side on an ESEE 5.

 

[Uncle Timbo]

I'm not sure I would ever use the term "too sharp" ... but I believe you can definately sharpen a blade til its to thin to last long ... it may shave like a razor but for how long?

And as some said already ... every edge sharpened to the geometry that best suits its intended use is sharp ... sometimes that's staying at a very toothy low grit instead progressing up to fine micron polishing of the edge to reach the "mirror finish".

Thank you, Mr. Colt. This goes back to my pencil analogy.
I'll stop sharpening my, "pencil" if you will, before it gets, to that very fine point. Bear down on that very fine point and it's not going to last for everyday use.

 

[singularity35]

How do you define "too sharp"?

 

[Uncle Timbo]

How do you define "too sharp"?

Great question! I wish I had a great answer. I'll tell the story of where my Dad worked at a chemical plant in WV where I grew up. A salesman came one day with a new product in a sealed cardboard box. I hear all you hillbillies carry sharp pocket knives, somebody give me one so I can open this box. Everybody said, Harold, give him yours. Dad pulled out his Tree Brand Stockman, and opened up the coping blade (which was shaving hair sharp) and handed it to him.
The salesman sliced thru the cardboard and said, damn, those guts were right about you hillbillies.
Dad said, of course I had to resharpen it that evening.
So, that blade, was too sharp for that particular task. Dad knew it, but wanted to have some fun with the city slicker.

 

[singularity35]

Great question! I wish I had a great answer. I'll tell the story of where my Dad worked at a chemical plant in WV where I grew up. A salesman came one day with a new product in a sealed cardboard box. I hear all you hillbillies carry sharp pocket knives, somebody give me one so I can open this box. Everybody said, Harold, give him yours. Dad pulled out his Tree Brand Stockman, and opened up the coping blade (which was shaving hair sharp) and handed it to him.
The salesman sliced thru the cardboard and said, damn, those guts were right about you hillbillies.
Dad said, of course I had to resharpen it that evening.
So, that blade, was too sharp for that particular task. Dad knew it, but wanted to have some fun with the city slicker.

I actually disagree. If a tool has a certain quality is "too XXX" then it would make that tool inefficient or unsuitable for the task. Since your dad's knife did fulfilled it's task admirably, then it could not have been too sharp. The quality of "too sharp" was merely defined as such by a user who wasn't used to the level of sharpness of your dad's tool.

My definition of too sharp would be a level of sharpness that makes the tool inefficient or unsuitable for the task. Sharpness is usually a description of how a cutting tool performs in it's task. Quantitatively, it's a measure of the apex of both planes of a cutting edge. Theoretically, an edge can be one molecule thick. Of course, thickness behind the edge matters in how an implement cuts but it also matters because the material behind the edge is what gives the edge it's strength. Some materials can support a very thin edge and still perform suitably for the task designed. Additionally, some tasks require an edge bevel of 90 degrees inclusive.

My conclusion there is that if a knife cuts well(efficiently) what it is supposed to cut, the sharpness limit then becomes the ability of that edge to keep performing efficiently. If the level of sharpness of an edge then does not allow it to keep performing efficiently for a reasonable amount of work, that is one indication that it is too sharp.

 

[adamlau]

An apex can absolutely be too sharp for a given task.

 

[Uncle Timbo]

I actually disagree. If a tool has a certain quality is "too XXX" then it would make that tool inefficient or unsuitable for the task. Since your dad's knife did fulfilled it's task admirably, then it could not have been too sharp. The quality of "too sharp" was merely defined as such by a user who wasn't used to the level of sharpness of your dad's tool.

My definition of too sharp would be a level of sharpness that makes the tool inefficient or unsuitable for the task. Sharpness is usually a description of how a cutting tool performs in it's task. Quantitatively, it's a measure of the apex of both planes of a cutting edge. Theoretically, an edge can be one molecule thick. Of course, thickness behind the edge matters in how an implement cuts but it also matters because the material behind the edge is what gives the edge it's strength. Some materials can support a very thin edge and still perform suitably for the task designed. Additionally, some tasks require an edge bevel of 90 degrees inclusive.

My conclusion there is that if a knife cuts well(efficiently) what it is supposed to cut, the sharpness limit then becomes the ability of that edge to keep performing efficiently. If the level of sharpness of an edge then does not allow it to keep performing efficiently for a reasonable amount of work, that is one indication that it is too sharp.

Hello Adam - I loved your explanation, but I too have a thought, if Dad were using a surgeon's scalpel, would that not have done the job as you say, admirably?

 

[stitchawl]

Stitchawl:
I don't think you can make an edge too 'sharp.'
I DO think you can make a sharp edge too 'thin.'

Don't they sort of go hand in hand?

They 'could.' But they don't necessarily have too.
You can make a very sharp edge on a thick file by grinding then honing a shallow angle. The apex can still be very sharp. However, it might not be suitable for cutting many things despite being so sharp. Conversely, you can make a dull, thin razor blade that won't even cut your finger.


Stitchawl

 

[singularity35]

Hello Adam - I loved your explanation, but I too have a thought, if Dad were using a surgeon's scalpel, would that not have done the job as you say, admirably?

If opening 1 small box is what it is required to do, then it might be a suitable implement for that task. If it were required to open and cut up multiple 3 ply cardboard boxes, the scalpel would probably be unsuitable.

 

[brasileiro]

They 'could.' But they don't necessarily have too.
You can make a very sharp edge on a thick file by grinding then honing a shallow angle. The apex can still be very sharp. However, it might not be suitable for cutting many things despite being so sharp. Conversely, you can make a dull, thin razor blade that won't even cut your finger.


Stitchawl

Exactly. It’s my thought but I couldn’t find a mathematical balance between angle-thick. Is there a mathematical proportion for the relation between sharpening angle and bevel thickness?

I.e. I sharpened a blade with 20 dps with no micro bevel at 600 grit then strop just to remove the burr off. Shaving sharp. But the thickness of bevel is about 0,5mm +- 0,02”. I also sharpen another knife with the same way but the bevel has about 1mm thickness. Frustration. What I mean is what angle should I use for a certain thick.

Thanks.

 

[HeavyHanded]

Frustrating when you go to open a cardboard box and instead of tracking between the flaps it fillets the cardboard...

 

[me2]

If the knife had to be resharpened after one box, either it wasn't sharpened properly or his sharpness standards require essentially a fresh edge after every use.

A knife cannot be too sharp, however it can be too thin or the edge angle too low. For cardboard, food, or similar material, the limit of geometry is quite low. I've put 3 degree per side primary grinds on 1/32" stock, with 7 degree edge and 10 degree microbevel and cut cardboard with no damage. Some people put hair whittling edges on basically cold chisel geometry blades, with 50+ degree inclusive edges.

 

[Lapedog]

If the question is can an edge be too sharp due to geometry? To make the knife sharper we make the edge thinner, then yes there is a point where it has become too thin and no longer is viable to be used. Depending on the intended work at what point too thin is will vary.

There is another way the question could be interpreted. Can a knife edge be too keen? As is if we look at the apex with a microscope we won't see mini serrations assuming maximum keeness. Again the answer is yes. For certain jobs a toothy edge is better.

Can a knife edge be too sharp?

Yes, if the knife is a trainer!

 

[Uncle Timbo]

I wish my Dad were alive today. Some of you were right, he kept that particular blade, hair popping sharp.
When guys where he worked would bring their knives to him for sharpening, he'd always ask, are you going to cut up cardboard with this or shave hair and impress your friends? He'd sharpen accordingly.
I don't know if that box the salesman cut up was 1 ply or 5. I know Dad worked in the maintenance dept., so it could of been industrial grade.

I have a question, do some of you sharpen your knives uber, hair shaving sharp, for every-day menial tasks? If so, do you ever do outside chores with it? Work in the garden? Take it camping? Fishing? I'm just curious.

 

[Sonnydaze]

I think that the working sharpness of the apex...or the minimum included angle...that won't be easily chipped (too hard) or rolled over(too soft), is dependent on the blade-steel you're working with...as well as what you're cutting. So I guess it all just...depends...

 

[Sonnydaze]

I wish my Dad were alive today.
I have a question, do some of you sharpen your knives uber, hair shaving sharp, for every-day menial tasks?

Yeah, I miss my Dad...
I don't try for uber-sharp...I am usually happy with 600-to 1000 grit...and a toothy edge is preferable for my very "casual" cutting.

 

[brasileiro]

Yeah, I miss my Dad...
I don't try for uber-sharp...I am usually happy with 600-to 1000 grit...and a toothy edge is preferable for my very "casual" cutting.

Im new on sharpening world. I made some tests like I wrote previously. It was not my intention at all to get shaving sharp on that knifes. I just stop at 600 grit and strop to remove some left behind burr. Do you strop after 600 grit or you remove the burr with same stone? Thanks.

 

[adamlau]

I have a question, do some of you sharpen your knives uber, hair shaving sharp, for every-day menial tasks? If so, do you ever do outside chores with it? Work in the garden? Take it camping? Fishing? I'm just curious.

This goes back to what others have already mentioned: Different knives are sharpened at different angles using different grits for different tasks. I am not taking a gyuto in R2 at 10 dps out to the garden.

 

[Obsessed with Edges]

I wish my Dad were alive today. Some of you were right, he kept that particular blade, hair popping sharp.
When guys where he worked would bring their knives to him for sharpening, he'd always ask, are you going to cut up cardboard with this or shave hair and impress your friends? He'd sharpen accordingly.
I don't know if that box the salesman cut up was 1 ply or 5. I know Dad worked in the maintenance dept., so it could of been industrial grade.

I have a question, do some of you sharpen your knives uber, hair shaving sharp, for every-day menial tasks? If so, do you ever do outside chores with it? Work in the garden? Take it camping? Fishing? I'm just curious.

I try to, more or less. How sharp I make my edges is essentially the result of sharpening habit, as I've spent a long time learning how to do it in a reliably repeatable manner (practice effective & repeatable habits => get effective, repeatable results). I think I already stated so earlier in the thread, but I've been in the habit of getting them as sharp as I'm capable of making them, within the limitations of the steel, the geometry and the desired edge finish (coarse/fine/mirror/etc). Most of the time, that usually results in an edge that'll shave some hair, at least. Some uses don't need that degree of sharpness, but it's OK. After the shaving sharpness degrades a bit, the edge is still good for 99% of the work I do with it. I might put off resharpening or touching up a little longer, for some knives that don't shave anymore, but still get the job done to my satisfaction. But when I do take the time to touch them up again, I always shoot for the same target result.

The exception might be if I have some sort of edge damage that needs immediate attention to get the work done; I do what I can, on the fly, to get it working in the short term. But that's soon followed by 'fixing it for real' later, when I have access to all the tools I prefer to use, and have the time to do it the way I really want it done.

I think it's sort of pointless to deliberately dial back my effort, solely because I don't really need the sharpest edge for a certain use. I do what I always do by habit, and it becomes essentially automatic and relatively easy to get the same results, or very nearly so, all the time. It's easier that way. And in particular, setting up good cutting geometry the first time makes all maintenance that follows a LOT easier, in hitting the target for sharpness. Even menial tasks are lot more enjoyable when doing them with a truly sharp edge; that's a great motivator to keep giving it the best effort.


David

 

[singularity35]

I have a question, do some of you sharpen your knives uber, hair shaving sharp, for every-day menial tasks? If so, do you ever do outside chores with it? Work in the garden? Take it camping? Fishing? I'm just curious.

When I'm done sharpening my knives always shave armhair with ease but I don't consider this uber sharp. I used to sharpen to hair splitting edges before and wouldn't carry a knife less sharp than that. Experience showed me that that hair splitting edge is gone in a few cuts and the edge settled down to a useful level for some time. I usually refined my edge down to around 1 micron or .5 micron finish too. Turned out that that kind of edge wasn't ideal for my uses.

My edges(and preferences) have evolved to a 600-800 grit finish that easily shaves armhair. I have found that this kind of edge(dependent on the steel, of course) suit my uses well.