Tests of edge holding ability?

[candlelight001]

Ok, I'm new at the sharpening game. I've figured out how to get a shaving, paper slicing edge on my knives, somewhat reliably. Now I want to know whether I'm putting a lasting sharp edge on it, or just the so-called "wire edge," or something else that will collapse immediately. Obviously I could just use it a while and observe, but it seems like it would be hard to get consistent data from that.

What I'm thinking is: first sharpen to shaving sharp. Then make X number of 18 inch cuts into cardboard, then try shaving test or paper cutting again. Under this scenario, what would be a reasonable number of cuts that I could expect to make without losing too much sharpness? Also, is shaving the right test or is it too high a bar after cutting cardboard? Are there other tests that come to mind?

Knives involved include a Delica and a couple Bark Rivers.

Thanks!

 

[siguy]

i don't know about testing, i just check for a visible burr. if i can't see it, then it isn't big enough to cause a problem for me.

if you hold the knife edge down under a bright light, you can see if there is a burr. my example is exaggerated, but it dispays the principle;

non burr side:

burr side:

even very very tiny burrs will show up this way.

you could do it cliff stamp style and do a measure of cutting force by laying a cord on a cutting board on a scale (calibrate scales to zero) and then see how much weight it takes to push straight down through the cord. this will give you an idea of amount of edge degradation. you would do this after your tests...

 

[Zeasor]

...What I'm thinking is: first sharpen to shaving sharp. Then make X number of 18 inch cuts into cardboard, then try shaving test or paper cutting again. Under this scenario, what would be a reasonable number of cuts that I could expect to make without losing too much sharpness? Also, is shaving the right test or is it too high a bar after cutting cardboard? Are there other tests that come to mind?...

No one can reliably tell you how sharp your blade should be after X number of cuts. For such a standard to be meaningful, someone would have to test a blade of the same steel as yours with the same bevel geometry and the same sharpness with and without a wire edge or burr after which the resulting sharpness would have to be tested in some standardized, repeatable way. I doubt you will find such a test; way tooooo many variables. Try this. Sharpen your blade to the point that it seems as sharp as a new box-cutter type blade. Make similar cuts with your knife and the box cutter blade. If your knife doesn't dull significantly more than the box cutter, you probably don't have a wire edge. Of course, now you have to re-sharpen your knife with the potential for creating a new wire edge.

It is best to check directly for a burr. One highly sensitive way to check for burrs is with a needle. Very lightly slide the needle point down the bevel toward the blade edge on each side of the blade. The needle point should slip smoothly off the edge on both sides. If you sense a "lip" or a "catch", you have a burr.

 

[Jason B.]

Strop to remove the burr, your knife will be sharper and your edge will last longer. Everyone has their own method of checking for a burr and here's mine, Place the knife at your sharpening angle on the top of your thumb nail, use a stropping motion away from your finger and if their is a burr it will scrape the nail surface. This is the only method I have found that will detect a burr past 8000 grit.

 

[Bernoulli]

I've read about a rope cutting test. If I remember correctly, you make (counting) clean cuts through the rope until you can't cut cleanly with one swipe. You could then compare that number with other knife performances. Obviously there are many variables here - what kind of steel and so forth. Dendritic steel held the record.

 

[gud4u]

Testing edge-holding is generally a 3-step process:
- Test initial sharpness (paper-slicing, thread-cutting, etc.).
- Cut the test media (cardboard, rope, hardwood, etc.).
- Repeat initial sharpness test to test for reduced sharpness, edge-defects, etc.

I use newsprint-slicing for estimating sharpness, edge quality and edge defects. I use a slow draw-slice, since it test the full length of the edge. The newsprint-slicing provides audible, felt and visual feedback of edge quality or variations along the length of the blade edge.

For media, I use a hardwood tool handle, since it represents the hardest material I'm likely to slice. The test-cuts are full pointings of the hardwood tool handle. Any edge that passes two or more iterations with no perceptible loss of sharpness is a pretty durable edge.

Hope this helps!

 

[Broos]

Check for Wayne Goddard or Phil Wilson's posts - they test by cutting manilla rope on a scale, watching the weight placed on the scale to measure the force required for the cut. They both have provided some results of their testing here.

 

[knarfeng]

Check for Wayne Goddard or Phil Wilson's posts - they test by cutting manilla rope on a scale, watching the weight placed on the scale to measure the force required for the cut. They both have provided some results of their testing here.

I took my queue from these fine gents. I do my edge retention testing by cutting manila rope. The advantage as stated by one of the above are that you are only testing the edge, as opposed to the edge plus the blade profile. They also said that they got better correlation to real world cutting jobs performed by hunters, their target customers, with using manila rope as the cutting medium.

I don't have a scale. I use a 3x hand lens to examine the edges for reflected light before and after cutting. Reflected light equates to edge damage. For VG10, 154CM type steels, I examine the blades after 20 cuts. I use fewer cuts for lesser steels.