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Effects of different strop material on steel??????

Wed Nov 20, 2013 4:10 pm

I decided a little while ago to start with a mirror finish to determine the effect of any given stone or strop has on a knife edge or bevel. Not having high magnification equip. I judge the smoothness or toothiness of the actual edge by the scratch pattern left on a mirror finish (to the naked eye at least) on a bevel. Deeper scratches = toothy edge while a mirror finish on the bevel shoule leave a very smooth edge. This is my thinking and would appreciate any thoughts on if this is right or wrong and why.

So I recently created a flat mirror finish using the EP and up to a 16k Shapton glass stone. Then I used a balsa strop for the EP with .1 micron spray on it. It scratched the crap out of the bevel. I revomed these scratches quickly with the 8k Shapton. Up until I did this I have been able to use the Shapton glass stones through the 16k and then I would slice some phone book paper. The knife glides through the paper with a given feeling I get from the resistance the paper gives. Then I have used for example balsa strops with .5 CBN, .25 diamond spray then the .1 CBN. With each micron change the edge cut the phone book paper and I felt a little less resistance each time. I know this is not a very scientific test but it's the best test I can come up with. Since I can't see the edge under more magnification than 60x (if that is accurate) all I can go by is how the edge cuts. I have assumed the edge was getting sharper or smoother based on the edge cutting the paper with more ease. I have considered the different feelings I've felt were my imagination but I don't think that is true. So why did the balsa strop with very low micron seem to create a smoother edge (or did it?) scratch the mirror bevel all up? I'm assuming its because balsa wood is much coarser than the sprays I used. Does this sound correct? If so, is my edge apex toothier than I thought it was? I was basing that on the micron of the sprays without taking into account the effect of the balsa wood. Maybe balsa wood is a poor material to use very low micron sprays on.

The next thing I'm going to do is instead of using balsa strops, I'm going to use nano-cloth strops with the same sprays. I'll take a mirror bevel and strop it with the .5, .25 and .1 nano strops and see how they effect the mirror finish. If what I've read about nano-cloth is true the mirror finish should not be ruined. If anything it shoule improve the finish. Again, higher magnification would be nice but I'm not going to invest in any magnification tools right now. I have wanted to for a while but decided to wait or not get any at all. We'll see about that.

Of course that leaves me thinking about checking for the effect of the same sprays on leather. I've had good results of all these materials in the past as far as the sharpness of the edges. However the true effect of the different materials seems to have escaped me. Ken Schwartz has discussed this before and I kinda-sorta understood it I think. Or thought. But seeing it myself makes it far more clear.

I'm hoping I explained what I did and what I'm thinking ok. Any input or opinions about this is appreciated. I have no doubt all this has been discussed before but all my life I've learned far more after doing something rather than just reading about it. I've had electronics training before and my buddy could ace the test after the classroom lecture but I would not. However after performing the material covered in class on a bench and seeing the results of applying the knowledge I finally "got it".

Another thing I've found is even when I can feel the differences in an edge after progressing from stone to stone or strop these little differences make little difference when cutting a piece of meat. The only time I can tell any difference is if the edge is very toothy or very smooth but very sharp. I can feel the difference in a toothy or smooth edge on a tomato. We may be using the words "smooth", "toothy" and sharp and they mean slightly different things to different people.

Re: Effects of different strop material on steel??????

Thu Nov 21, 2013 8:39 am

One thing you have to consider is that diamond spray particles have very, very sharp edges. Even though they're extremely fine particles, they are still very sharp and can (and will) leave scratches in mirror finishes. It's one thing I do like about stropping on felt with diamond spray. It leaves a very refined, toothy edge. I can mirror polish the edge with my Superstone 10k, and then scratch it up a bit with very fine diamond spray.

Re: Effects of different strop material on steel??????

Sun Nov 24, 2013 2:48 am

The nanocloth will not 'add' a scratch pattern as balsa and other woods do at the finer grits. Cow and horse leather and felt will leave a coarser 'background' than kangaroo leather which only marginally competes with the scratch pattern of the compounds themselves.

If you see scratches when using nanocloth, it is typically from 'uncovering' scratches caused by preceding abrasives - either stones or coarser compounds. It is BY FAR the least likely surface to impart any additional scratches, leaving a pure compound only effect. Also poorer quality compounds can have coarser particles in the mix with resultant scratches or particles clumped together in poorly constructed suspensions or slurries. Note also that for a given particle size polycrystalline diamond has many sharp corners of a finer size compared to a few larger edges, so the result is a finer and more consistent pattern.

Coarser diamond compounds tend to leave a somewhat more aggressive edge, but at the finer grits (again using good products) you will get an increasingly refined edge. Some of the 'toothy' effect of felt is more from tearing off burr, even without compounds.


Re: Effects of different strop material on steel??????

Sun Nov 24, 2013 8:26 am

I don't have any bare balsa right now so I can't slide a knife edge bevel on it to see what just the balsa does to the surface. But just thinking I wouldn't have expected a soft wood to do any harm (scratch) to any steel. Not visible to the naked eye at least. So, that leaves me thinking the CBN and diamond sprays I do have on balsa AMPLIFY the effect of the material it is used on. Maybe the micron level will make the amplification different. Don't know.

At my level of understanding right now I devide the use of abrasive anything on an edge into two categories. Polishing the bevel and sharpening the edge. A material/abrasive combination that will polish a bevel to a mirror finish will also put a very smooth edge on the knife. A material/abrasive combination that will scratch the crap out of a bevel that already has a mirror finish will leave a toothy edge. Does this basic theory hold water? The size of the toothiness (does anyone have a better word????) would compare to the size of the scratches left on the bevel I suppose.

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