Can't get a burr on my Sebenza..

Django606

Django606

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I decided to sharpen my Sebenza on my Sharpmaker with the flat medium stones set in the 40* slots. I was going to do one side until a burr was raised, then the other side until a burr was raised, and then switch to the white stones and do the same. This worked well on my BM Ares and I am very satisfied with the edge I was able to produce with these steps.

After sharpening on one side for about ten minutes, I could still not find a burr on the other side. I have heard people say that the Sharpmaker does not hit the edge properly on the coarse stones. Strange, considering the fact that CRK reccomends the Sharpmaker. The other day I had checked with the marker trick, but I had checked it on the fine stones. The edge did seem to be hitting the stones.

I guess the only answer is to reprofile it, right? A diamond benchstone is out of the question, because I know I will just mess up the edge, and the aesthetics of the knife are important to me. I have heard of people using strips of sandpaper stuck to the Sharpmaker stones, so the angle is kept, but a much coarser abrasive can be used. Is this what I should do? I think I read that Sebenzas come with around 22* bevels. Can only 2 degrees make it impossible to hit the edge when sharpening on the Sharpmaker?
 
Yes, even a slight change in angle will prevent the edge from getting sharpened until you grind off all the extra metal and reduce the bevel to the Sharpmaker setting. Since S30V has a very low grindability this can take some time. Even if you are seeing the marker be removed along the edge there could still be a strip beyond the visible, say 0.1 mm wide which is too obtuse. However if this lasted more than a few minutes I think you may have another problem.

One way to make sure is to take a small section of the edge and just grind it lightly across with the edge of the Sharpmaker rods. This will flatten it and it will then reflect light there. If you go back to the rods at 20 degrees and give them just a few passes 5-10 and check this spot it will tell you what it going on. If the edge keeps reflecting light then you know it is still too obtuse and you need to reshape it, if the spot gets cleaned up rapidly and stops reflecting light then you are hitting the edge. If this is the case and it isn't forming a burr then you have much bigger problems. But before you get concerned about that, just see if that is the problem first.

-Cliff
 
Do you mean put the stone on a table and act like I was going to cut it with my knife? Which grit should I do this with, and which grit should I resharpen the 5-10 strokes with? I assume you mean alternating every side?
 
Django606 said:
Do you mean put the stone on a table and act like I was going to cut it with my knife?
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Yes.

Which grit should I do this with...
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Fine, the goal is just to flatten the edge so you can easily see it reflect light. This will happen almost immediately meaning about one cm of travel on the corner. If you did it on the medium it would cut a visble notch into the blade which is more than what is needed.

...which grit should I resharpen the 5-10 strokes with? I assume you mean alternating every side?
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Since you are trying to raise a burr you use the medium rods. If you are hitting the edge and not the shoulder you should see this flattened spot dissappear almost immediately as in you should see it reduce on almost every couple of passes. To be comprehensive do it in two places and work them on opposing sides and see how both sides react independently.

-Cliff
 
Ok, I just did about 15 strokes on the flats of the medium stones, and the section of the edge is still reflecting light. So this means I have to reprofile in order to sharpen the knife in the 20* slots?
 
Ok that was the outcome I wanted to see, the edge is still too obtuse and there is a light convexity that you need to remove. Just grind away until those spots are not reflecting light and you know you are now hitting the actual edge and not the shoulder.

-Cliff
 
Should I flatten the rest of the edge so I can make sure it is all uniform as well? I assume that I should alternate sides every stroke until the edge stops reflecting light, and then grind one side until a burr, and the other, and so on?
 
You don't have to reprofile in order to hone all the way up to the apex of the edge and remove that flat spot. You simply have to continue honing at 20* until you make it all the way to the edge. On an extremely abrasion resistant steel like S30V this could take you an hour with a Sharpmaker. I don't think that your technique was at fault, you were simply underestimating how long it takes.
Go back to your initial technique and work one side of the edge on the edge of your medium rod. Don't get impatient and press too hard or you will damage your knife edge. Work one side till you get rid of most of your flat spot then switch over and hone the other side of your blade until you completely get rid of your flat. This is the pretty approach.

I prefer to reprofile edges to less than 15* per side so I would get a diamond sharpener and manually do some reprofiling. This is easy to mess up and scratch up your blade.
 
Django606 said:
Should I flatten the rest of the edge so I can make sure it is all uniform as well?
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You can.

I assume that I should alternate sides every stroke until the edge stops reflecting light ...
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You can just grind one side full and then the other which is much faster usually. Note when you remove the flat on one side you will want to create it lightly again if you are using this to check the other side. Though this seems like a lot of work you only have to do it once.

-Cliff
 
Thanks for all the input guys. So I should be using the corners until I remove the flattened edge, then the flats when I want to grind one side until I get a burr, then the other side, etc. Right?

Tell me if I interpreted this right. After I flatten the entire edge, I should sharpen one side on the corner of the medium stones until the edge is no longer flat. After this, re-flatten the blade and do the same with the other side?

Seems like an awful lot of work just to start sharpening. I hope the edge turns out as sharp as my Ares :eek:
 
Django606 said:
Thanks for all the input guys. So I should be using the corners until I remove the flattened edge, then the flats when I want to grind one side until I get a burr, then the other side, etc. Right?
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Yes, generally the corners are for shaping and the flats for sharpening, aside from curves which you can't actually match with the flats.

After I flatten the entire edge, I should sharpen one side on the corner of the medium stones until the edge is no longer flat. After this, re-flatten the blade and do the same with the other side?
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Yes, again you are just lightly grinding into the edge to provide a visual benchmark. You don't actually need to do this, you can just keep grinding until you note the burr form by checking the edge under magnification, by feel with the finger, or how it effects the cutting ability. Flattening the edge just makes it trivial to verify visually.

Seems like an awful lot of work just to start sharpening.
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It gets easier once you don't care what the edge looks like because you just take an x-coarse stone to the edge and hack it down to ten or fifteen degrees in about 1-2 minutes. You then use the Sharpmaker to apply the final edge bevel which is instant.

-Cliff
 
Ok, after sharpening some yesterday and some more this afternoon, I think I have gotten rid of almost all the flat. After I got rid of what I thought was most of it, I switched to the other side and kept grinding. Now the edge can slice cut paper. I still see some reflection when I shine a light on the edge.

Should I now alternate sides until the reflection is gone, or should I keep at it on one side until I achieve a burr?
 
Generally alternating tends to be more productive at creating a stronger edge. Staying on one side is just faster.

-Cliff
 
Also, what about the last 1/4 inch or so of the tip? Since Jeff said to use the corners of the stones, I have been avoiding that area so as not to round the tip (which I have done to a small degree :( )

The tip is ground at a more obtuse angle, and yet I still flattened it. That was probably a dumb move.

One side of the edge goes up towards the spine farther (don't really know how to explain this - does it mean a more acute angle?) than the other side. Could this be due to slight variation from the left and right stones? (I am much more comfortable with the left stone than the right stone, it just seems more awkward to me.)
 
Many primary grinds are not symmetric which means the edges will be uneven in width even when ground to the exact same angle. My small Sebenza is so uneven it even pulls to the side like a chisel grind cutting cardboard and I grind it flat to the stone so it is pretty much jigged at a precise angle.

With the tip you have to either regrind it, or alter your strokes to increase the angle near the tip. For a small knife like that I would prefer the tip to be more acute than the main body of the blade not less, so I would regrind it. What you can do is just focus on the tip by itself and do it carefully.

-Cliff
 
If I want to keep the tip more obtuse, do I just tilt my hand to match the angle? So does this equate to tilting my hand toward the stone I am grinding on when I get to the tip?

My Ares was the same way, except the opposite. The angle was more acute by the tip, and tilting away from the stone fixed this. I am assuming it is the opposite for a more obtuse tip?
 
Tilting towards the stone gives a more acute angle, going to zero with the blade resting on the stone.

-Cliff
 
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