What makes a knife sharp?

J

joejoe

Guest
What makes a knife sharp, I know how to sharpen a knife and all that, but what actual makes the knife sharp? Hope I am making sense to a least some of you.

Joejoe
 
Do you mean what constitutes "sharp" or do you mean what exactly is the physical process that renders something "sharp" ?

Or something else?

(What an amusingly unusual question BTW :))
 
any help here:

JoeJoe: There's a hole in my bucket, dear Liza, dear Liza, There's a hole in the bucket, dear Liza, a hole.

Liza: Well fix it dear JoeJoe, dear JoeJoe, dear JoeJoe, well fix it dear JoeJoe, dear JoeJoe, fix it

JoeJoe: With what shall I fix it, dear Liza, dear Liza, with what shall I fix it, dear Liza, with what?

Liza: With straw, dear JoeJoe, dear JoeJoe, dear JoeJoe, with straw, dear JoeJoe, dear JoeJoe, with straw.

This goes on in the same format with different lines:

But the straw is too long.
Then cut it.
With what shall I cut it?
With a knife

But the knife is too dull.
Well sharpen it
With what shall I sharpen it?
With a stone

But the stone is too dry
Then wet it
With what shall I wet it?
With the water

But where shall I get it?
In the well
With what shall I fetch it?
With the bucket

But there is a hole in the bucket dear Liza...
 
Looks like a team of researchers at UCD are on the leading edge of this topic.

They state quite bluntly that


But they make a good stab of coming up with a new definition.
 
Remix said:
Looks like a team of researchers at UCD are on the leading edge of this topic.

They state quite bluntly that


But they make a good stab of coming up with a new definition.
Click to expand...

more like the cutting edge.

Joejoe
 
uiop said:
Maybe you can view it in terms of the equation below:

Pressure (Pascals) = Force per unit area (Newtons per metres squared)

Assuming the material of the knife is hard. The thiner the edge,then the smaller the area of the cutting edge and hence the higher and more concentrated the pressure is when a force is applied.

Make any sense ?
Click to expand...

Ok that make sense, so how do gauge how sharp my kitchen knife is?

I find is amazing that a knife with so little pressure / effort can cut.

Joejoe
 
I read in a cook book before that a rule of thumb is if you draw your blade across a tomato without pushing down on it and it cuts the skin then you have a suitably sharp knife. The key is to sharpen it little and often to maintain a good edge. I always give my knives a quick sharpen before each use.
 
Last edited:
uiop said:
It depends how you want to define 'sharpness' . You can define it according to the P=F/A equation. The 'sharper' it is, the greater the pressure at the point of application.
Click to expand...

so how narrow is the edge of a very sharp knife?

Joejoe
 
joejoe said:
another pointless post by Clubman.

Joejoe
Click to expand...
It answered the question as originally posed as far as I can see.

Glad you found Brendan's nursery rhyme answer less pointless than my answer to your question. :rolleyes:

I don't know why I'm bothering but these links which took about ten seconds to find with might be of interest:

[broken link removed]
[broken link removed]
 
I find a relatively cheap serrated-blade knife (about the size of a standard bread knife) is the best for all-round kitchen work. It cannot be sharpened, and has a limited life span of maybe 6 years in constant use, but it cuts beautifully, and passes the 'tomato test' effortlessly.
 
joejoe said:
What makes a knife sharp, I know how to sharpen a knife and all that, but what actual makes the knife sharp? Hope I am making sense to a least some of you.

Joejoe
Click to expand...
Buy and let us know if it's any good.
 
Purple said:
Buy and let us know if it's any good.
Click to expand...

I didn't think it was much good when I flipped through it at the book shop.

I could never get the hang of sharpening and tried many different tools (steel, wheels, stones etc), until I came across this: http://www.amazon.com/Furi-Ozitech-Diamond-Fingers-Sharpener/dp/B000F8SIOW which works absolutely perfectly. My knives are now like razors and sharpening is as simple as drawing the blade through this a few times before use.
 
This link gives a useful primer on sharpening theory (courtesy of Ron Hock, blade maker)

[broken link removed]

It's worth remembering that stainless steel blades (as most kitchen knives tend to be) are not the best material for taking and holding an edge- sharpenability and toughness suffers because of the metallurgical composition which renders them "rustless" (high carbon content aids sharpenability whereas chrome content (in stainless) is required for corrosion resisitance. So there!
 
Carpenter said:
This link gives a useful primer on sharpening theory (courtesy of Ron Hock, blade maker)

[broken link removed]

It's worth remembering that stainless steel blades (as most kitchen knives tend to be) are not the best material for taking and holding an edge- sharpenability and toughness suffers because of the metallurgical composition which renders them "rustless" (high carbon content aids sharpenability whereas chrome content (in stainless) is required for corrosion resisitance. So there!
Click to expand...

Thats very interesting, cheers Carpenter.

Joejoe
 
What makes a knife sharp? If you remove the blunt, what's left is the sharp.
Simple, ask anyone in Limerick
 
When it slices through your thumb - requiring 5 stitches and a permanent loss of feeling - instead of the frozen cheese you were aiming at, it's sharp. Trust me on this one.
 
You must log in or register to reply here.
Back
Top