Sandpaper sharpening scratches above bevel

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faffo99

Joined
May 6, 2014
Messages
4
Hi there, this is my first post.

I'm new to knives and I'm just getting to learn the sharpening.
I have a Spyderco persistence that is now being customized so i'm practicing with a cheap Opinel 8.

I had very good advices from a friend of mine on how to sharpen with sandpaper, convex sharpening i should say. I use 400 (only when bad blade) then 800, 1200 grit. I use the strop movement and at the end I strop on a used leather belt.
I must say I have wonderful results regarding the sharpening, very razor sharp knives..they cut very precisely and keep the edge for quite long.

I sharpen on a self made "gadget" with wood and that kind of "foam" as the one used for mouse pads 0.11 inches thick. I attach a picture of it.

The only problem i have is that when i'm done sharpening i get a whole strip of scratches above the bevel...a sort of satin halo, quite uniform and precise along the knife. I attach a picture of it as well.

Can any of you tell me how come this happen? I set the knife at 20° angle and, considering how sharp it comes out, i believe it is right...plus i pay attention not to be too close to the sandpaper with the blade.
I must say I don't put much pressure...but, could it be it?

Thanks for any of your precious answers!

P.S. aside from knowing why they appear, any hint on how to get them removed?


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faffo99, protect your blade above bevel using duct tape before sharpening to avoid unnecessary scratch. this is classic problem of sharpening using sandpaper with flexible backing such as leather or mousepad.
 
I will second the "too much pressure" statement from NSW1535. I had this same issue and when I decreased the pressure, the scratches stopped appearing. As for removing them... To my knowledge, once scratches are there, they are there to stay.
 
Sorry but you are all incorrect.

The picture looks fine to me but the reason you are seeing the "scratching" is because a contrast of different direction in the scratch pattern. The factory grinding is vertical and your grinding is angular creating a contrasting scratch pattern.

Sharpen with the vertical factory grinding marks and your "scratches" will disappear.
 
The scratches above or further up from the actual bevel your were grinding look to me like they would be caused by the foam backing. Allowing the sandpaper to form over the primary bevel. I have been recently sharpening with sandpaper taped over a stone,and I have not had your problem. I could be wrong, but that's what it looks like to my eyes. I understand what knifenut1013 said, but I think the OP was wondering why there was a scratch pattern further up on the blade, above the primary grind.
 
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Could be some slack in the paper making a ripple that rides a touch off the foam. In any event it can be eliminated by switching to a harder backing.
 
Wow guys, thank you! I wasn't expecting so many answers!
So, maybe next time i'll mix up all your answers adding duck tape to the blade + using a harder backing + applying very low pressure or none, this might solve the problem I hope!

Since I bought this Opinel to practice sharpening, can any of you tell me how to remove or at least reduce the scratches i just made on the blade in order to be able to see with the next sharpening if got any better?

As it is right now i'm afraid i won't be able to see the difference of scratches on scratches....thank you very very much!
 
faffo99 said:
Wow guys, thank you! I wasn't expecting so many answers!
So, maybe next time i'll mix up all your answers adding duck tape to the blade + using a harder backing + applying very low pressure or none, this might solve the problem I hope!

Since I bought this Opinel to practice sharpening, can any of you tell me how to remove or at least reduce the scratches i just made on the blade in order to be able to see with the next sharpening if got any better?

As it is right now i'm afraid i won't be able to see the difference of scratches on scratches....thank you very very much!
Click to expand...

Make some Sharpie marks from spine to edge similar to the pic. After a couple of passes you'll be able to see exactly where you're making contact.

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Ok guys i did as heavyhanded suggested, i drew some marks on the blade, then dulled the knife and sharpened again. This time I used a proper mouse pad and i believe it works! Maybe the problem was that the foam used previously didn't have that thin layer of plastic on it which provides sturdiness above the foam.

attach some pics...

p.s. still no hint on how to remove previous scratches, maybe a cotton wheel with some sort of compound?

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HeavyHanded said:
Could be some slack in the paper making a ripple that rides a touch off the foam. In any event it can be eliminated by switching to a harder backing.
Click to expand...

:thumbup:
That sums it up. The firmer the backing is, the less tendency there will be for the paper to curl or ripple under the blade. The grind pattern will stay closer to the edge where you want it. This can be improved further, by using some temporary adhesive (or adhesive-backed sandpaper) to firmly afix the paper to your backing. You'll still get some nice convex (that's more to do with the stropping technique, when done freehand), and resulting edges will be much crisper at the apex, as well. There's literally nothing to give up, and much to gain, in using a more firmly-backed setup.

Edited to add:
Giving yourself a larger surface to work upon also helps. If you're not already, use the full length of a sheet of wet/dry paper for your strokes. It's more difficult to produce a nice, clean & straight grind pattern in a short stroke, as there will always be some wavering if one has to abruptly halt the stroke on a shorter abrasive surface. A longer, sweeping stroke is easier to maintain in a linear direction, and the resulting grind pattern looks much better. This is also a good reason to afix the paper with adhesive, so you don't have any clamps or other paper-holding rigging to dodge while you're sharpening.


David
 
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faffo99 said:
Ok guys i did as heavyhanded suggested, i drew some marks on the blade, then dulled the knife and sharpened again. This time I used a proper mouse pad and i believe it works! Maybe the problem was that the foam used previously didn't have that thin layer of plastic on it which provides sturdiness above the foam.

attach some pics...

p.s. still no hint on how to remove previous scratches, maybe a cotton wheel with some sort of compound?
(...)
Click to expand...


Many of the coarser scratches can be lessened over time, by doing your touch-up maintenance on higher-grit paper; that could be anything from 400-2000+, depending on how coarse the scratches are, and how refined you want the finish to look. Again, this is where a firmer backing for your setup will make the paper work more aggressively, so that can speed things up. Jason's (knifenut1013's) tip about focusing on keeping the strokes in line with the factory grind will help as well. I wouldn't worry too much about trying to fix it all at once (rushing the process, for me anyway, tends to produce less-than-perfect results ;) ). Choosing the right stropping setup & compound can also go a very long way toward cleaning it up over time, and polishing as well. I've found a 'white rouge' compound to work very well for this; it polishes quickly. Some of the finer black compounds do this well also. Very coarse scratches will hang around much longer, but I wouldn't worry too much about those. In time, with some patience and strategic choosing of materials and methods for touch-ups, the heavier scratches will fade away.


David
 
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