Paper Wheels...do they concave an edge?

M

Marvin8

Joined
Jan 18, 2010
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403
I've been told that since wheels are round, and typical flat edges are v-shaped, the use of a grinding or honing wheel will tend to concave or hollow a straight edge, thus weakening it ever so slightly. This guy said that a straight v-edge should only be sharpened against a straight edge. Any truth to this? Seems to make sense, but perhaps it's an exaggerated fear. I'm too new to this to know for sure.

Thanks for your thoughts.
 
I think you have received the opinion of a person that does not like paper wheels.

Pretty much every sharpening method that you will see supported on this forum will achieve a great result for most uses. If you want to get really carried away and start splitting hairs (figuratively), some methods are better for some uses. If on the other hand you just want to literally split hairs, many of the methods here will work LOL.

To the point, wheels are round and they do produce hollow grinds. Hollow grinds are "best" for some uses. Perhaps the opposite is a convex grind which is also "best" for some uses. Somewhere in between is a true V grind (flat) which is also "best" for some uses. Bigger wheels will produce a larger radius grind and the result gets pretty close to flat. Notice I am discussing GRINDS here which effects the entire blade shape. If you are just sharpening (which it sounds like you are), the geometry of the bevel is even more subtle (than blade grind geometry) in terms of performance...I bet you would need a pretty finicky user to discern the difference in cutting performance in a blind test. I would not sweat it too much personally.
 
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Any grinding wheel, like a paper wheel with Silicon Carbide coating, will hollow grind an edge. The smaller the wheel diameter, the more pronounced the concavity will be. Hollow grinds are weaker, generally speaking, than either flat V or convex grinds. That being said, I still prefer its level of sharpness in some applications. There is a difference between a grinding and honing wheel though. The honing wheel in a paper wheel system polishes an edge and does not hollow an edge so much. I don't do it, but it is possible to use the paper honing wheel to polish a flat or convex edge.
 
The paper wheels can turn your knife into a recurve, if you use them often and press too hard. I don't think it would "weaken" the edge any more than any other method of sharpening, unless you let it get hot.
 
Additionally, think if trying to hold the blade at the exact, same angle across the blade blade while sharpening. Unless you are using a jig, you can get close, but not perfect.

A close inspection of the actual edge will most likely reveal that like any free hand sharpening result, the edge itself will be a be a tiny bit convex, not concave.

Robert
 
midnight flyer said:
Additionally, think if trying to hold the blade at the exact, same angle across the blade blade while sharpening. Unless you are using a jig, you can get close, but not perfect.

A close inspection of the actual edge will most likely reveal that like any free hand sharpening result, the edge itself will be a be a tiny bit convex, not concave.

Robert
Click to expand...


:thumbup:

I have found the wheels to produce a convex edge over time. Since you change the angle each time by very small amounts it ends up convex after many sharpening sessions but this happens with just about all free hand sharpening.

Since the very edge of the blade is so small and the contact footprint on the wheels is so small, it is essentially flat at that spot. If it did produce a concave shape it would be so small and would probably be on the order of hundredths of a millimeter and would be unnoticeable and certainly would not effect strength.
 
That's pretty much what I figured...much ado about nothing, mountain out of a molehill.
I guess that the bigger the wheel, the less of a concern. I'll have to see what kind of edge comes on my Griptilian, but I suspect that it's a typical flat 20º edge.
 
unit is correct. most guys who dont know a thing about paper wheels will talk down about them. they are usually guys who have tried to use them but just dont have what it takes to figure out how to use such a simple device for sharpening their knives.

the wheels produce a v edge that looks just like you used a stone but a lot quicker and sharper.

the wheels wont turn the edge into a recurve like samhain73 said. if this is happening then you're not sharpening correctly or your abrasive wheel needs trued and recoated properly.
 
Does it make much of a difference between using a 6" wheel vs an 8" wheel? Do most grinders have the ability to reverse the wheel direction, or is it just a matter of turning the grinder around to face the other direction. Any major suggestions for grinders, other than that Harbor Freight company? All the grinders I've seen are around 3500 rpm. Seems a bit fast, no? Is there a separate thread for "how to choose a grinder"? And what grit is recommended for the "grinding" side? I know the other side is the honing side. Muslin? Cotton? Sorry for all the questions.
 
marvin8, i have used the wheels for 18+ years and i havent found anything yet that can compare to the speed, quality of edge and ease of use the wheels give. check out the vids at my google website. i used to sharpen by hand and i wouldnt take $10. an inch to sharpen a customers knife by hand when i can give him the same if not better results a lot faster for $1. per inch. even guys who used cloth, sisal or leather wheels liked the paper wheels edge a lot better.
read my tips page for more info and read more at my website http://www.bladeforums.com/forums/showthread.php?t=608864
 
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