Why do Sharpmaker corners cut faster?

J

Jamesh Bond

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Jan 14, 2007
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Spyderco recommends using the rod corners for faster metal removal. From what little i understand, this defies logic. I would think the flats would be more aggressive, as the surface area exposes more abrasive.

Could someone please explain this?

Thx.
 
The reasoning as I see it is that the pressure on the stone is concentrated in a smaller area.

If that makes sense. Not sure if I am right or not.
 
Dr_fosg8 has it the way I understand it also. Assuming you use the same applied pressure, the actual psi at the given point of contact is probably 20 times more on the corner than when applied across entire flat side. Thus biting harder and deeper.
 
dr_fosg8 said:
The reasoning as I see it is that the pressure on the stone is concentrated in a smaller area.

If that makes sense. Not sure if I am right or not.
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That's how they explain it, although I must say I'm still inclined to think that since any given spot on the blade will be in contact with the stone twenty or more times longer when using the flats, that it will sharpen faster that way.
 
bflying said:
Dr_fosg8 has it the way I understand it also. Assuming you use the same applied pressure, the actual psi at the given point of contact is probably 20 times more on the corner than when applied across entire flat side. Thus biting harder and deeper.
Click to expand...

Sounds logical to me. Also consider the ceramic is mixed with an aluminum (something or other) so that metal will be closer to the ceramic surface at the corners, thereby creating a slightly rougher area.
 
bflying said:
Dr_fosg8 has it the way I understand it also. Assuming you use the same applied pressure, the actual psi at the given point of contact is probably 20 times more on the corner than when applied across entire flat side. Thus biting harder and deeper.
Click to expand...
Like doing a regular push-up and then doing a push-up -- only on all ten fingers. Then do a push-up using only your thumbs and two fingers on each hand.

Your weight (the amount you're pushing) remains unchanged yet the pressure on your fingers/finger tips has increased exponentially because the weight is now concentrated on a much smaller surface area (your fingers/finger tips).
 
You may be applying more pressure on a smaller point but when you use the flats, that same point on the blade passes over the abrasive material 20 times more than on the flats. I tend to believe it balances out to being fairly equal. The only exception I can see is that when I run a pass on the flats, the blade isn't always making full contact with the stone. If that happens regularly, the corners will certainly be more aggressive.
 
The Deacon said:
That's how they explain it, although I must say I'm still inclined to think that since any given spot on the blade will be in contact with the stone twenty or more times longer when using the flats, that it will sharpen faster that way.
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Dang I should have read all the posts. Looks like you said pretty much the same thing I did.
 
But then again, if I want to take off material, I go to the EP or KME. I keep the sharpmakers out to touch up blades with already great bevels. ;)
 
If you want to cut a piece of printer paper, would you be more efficient with a blade with a 1/8" width or a 1/4" width. "Force per unit area" or "perpendicular pressure" says it all to me...has to do with all that Physics stuff we used to hear about.
 
al g blenny said:
You may be applying more pressure on a smaller point but when you use the flats, that same point on the blade passes over the abrasive material 20 times more than on the flats. I tend to believe it balances out to being fairly equal.
Click to expand...

This is assuming that the grinding action is linear. It may be that less force does not take off a proportionately less metal. I don't know, just proposing a possible explanation.
 
al g blenny said:
You may be applying more pressure on a smaller point but when you use the flats, that same point on the blade passes over the abrasive material 20 times more than on the flats. I tend to believe it balances out to being fairly equal. The only exception I can see is that when I run a pass on the flats, the blade isn't always making full contact with the stone. If that happens regularly, the corners will certainly be more aggressive.
Click to expand...
True, I can understand the advantage of using the corners when sharpening a serrated blade, a hawkbill, or one where the edge's shape contains some combination of convex and concave curves (recurve, reverse S, etc).

Still can't see it for straight edged blades, or those with only convex curved edges. By that logic, the Sharpmaker corners, or even the Sharpmaker flats,would sharpen a given blade faster than a 3" flat stone of equal grit, and I find that really, really hard to accept.
 
It's rather simple, the smaller contact area exerts more force on the edge which in theory will make it grind faster. In reality it causes massive deformation due to the high hardness and density of the ceramics.

When adding pressure to the grinding process it needs to be balanced out with a more friable abrasive in order to reduce over deformation of the edge. It's why you always hear "let the stone do the work".
 
Thx for the answers guys.

Jason, are you saying not to use the corners then, or simply to use them carefully?

Thx.
 
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