Hey guys, new to the group and I have a question I’m hoping someone can help me with. I’m basically a sharpening novice but have carried knives my whole life. I recently bought a worksharp precision adjust to be able to sharpen more accurately at home. I tried to reprofile my benchmade bushcrafter (s30v steel) and I’m not happy with the result. I set my sharpener to 20 degrees and worked through the stones (220, 320, 400, 600, 800, and ceramic). The knife is sharp, but one edge of the blade is probably double the width of the other. Before making matters worse, I wanted to get some advice. TIA.
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Reprofiling blade
- Thread starter e-wags
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Assuming you mean the bevel on one side (face) of the blade is twice as wide as the other side. You either have an off-center edge from grinding more on one side than the other, or the knife was tilted in the clamp causing a different angle from one side to the other.
I think that’s it! I bet if I measure the distance to the tip of the blade when facing each direction it’s further on the widened side. How should I approach correcting it at this point?
Yes the bevel, thanks! I’m pretty certain the spine of the blade was centered in the clamp but I’m thinking it wasn’t centered from left to right. How would you recommend fixing it? Will I now want to remove extra material from the “shorter” side of the bevel so it removes more at the edge, thus shortening the “longer” side?
... or make the short side ''longer''.
As the correction depends on this let us be clear. You believe that the blade was clamped directly on axis with the rotation of the clamp such that the angle ground on each side is the same? Looking directly at the edge of the knife from the perspective of material to be cut, you can see that the very apex of the edge is more to one side of the blade than the other?
This is an off-center edge, and it means you removed too much metal from one side of the blade. Because the metal that would have formed the apex in the centerline of the blade is now missing and you cannot put it back, you have taken some life off the blade. Correcting the centering by grinding on the "short side" will by necessity move the apex further up the height of the blade, taking off more life.
You need to decide if you want to use the knife as-is, correcting the centering in future sharpening by doing the majority of your strokes on the short bevel, or if you want to sacrifice that steel now to attain a centered edge. If you simply cannot stand how it looks then fix it now. But I would personally use it for a while and feel for "steering" when cutting. If you can still make a straight cut through cardboard without muscling the knife and if you can whittle adequately it likely isn't a usability problem.
When the edge is re-centered, now or later, it will be formed in a slightly thicker part of the blade. You will likely want to add a relief bevel above the apex bevel to keep cutting performance more like it was when new.
This explanation makes a lot of sense, thanks for expanding. I have some thinking to do because I hesitate to shorten the usable life of the knife. If I were to post some pics would that help guide the advice?
It might, so go ahead if it is not difficult. You'll need to upload to Imgur or similar.
The right side of the knife (edge down, point away) looks very good which makes me think your setup was OK. The left side has something funny going on at the tip. Can you take a couple of additional photos of that region with slightly different angles and lighting, including one from directly above the spine of the knife as straight and true as you can manage?
The right side of the knife (edge down, point away) looks very good which makes me think your setup was OK. The left side has something funny going on at the tip. Can you take a couple of additional photos of that region with slightly different angles and lighting, including one from directly above the spine of the knife as straight and true as you can manage?
I was trying to check for errors in the blade grind from the manufacturer. I cannot be certain without examining it myself, but I cannot see any so I will assume that the asymmetry is due to the edge grind.
On many knives the edge thickness increases as you approach the tip, as the edge moves up toward the spine into the thicker part of the stock. This is countered by the primary blade grind also sweeping upward but typically not at the same rate as the edge. This keeps the tip of the knife stronger—good insurance for most production knives—but it creates a complication for sharpening. If you want keep the edge bevel angle the same throughout then necessarily the bevel will be wider in this thicker area. Conversely if you wish to keep the same width of bevel throughout then necessarily the edge must be at a more obtuse angle in this thicker area.
It appears to me that you ground the right side of the knife to produce an even bevel width, then ground the left side in order to finish the apex. The tip region, being thicker behind the edge,* required more grinding which resulted in a wider bevel there. To correct this you would grind only on the right side near the tip, taking care to progressively blend this back through the belly of the knife. This will widen the bevel on the right side in that area, while narrowing it on the left. When complete the bevels on both sides will still be wider at tip than the rest of blade, especially since you have taken off some extra material near the tip, making the behind-the-edge thickness greater. There is nothing wrong with this but it may not be the look you desire. If you do fine cutting with the tip I encourage you to accept this look and enjoy the improved cutting performance of a lower angle edge.
If you desire an even bevel width from heel to tip then you must change the sharpening angle along the length of the edge, with understanding that this will reduce the fine cutting performance near the tip. In a clamped system this is done by the position of the blade in the clamp. Since I do not use a clamped system myself I am not practically familiar with the amount of angle-change heel-to-tip that is readily produced. Nevertheless even if you cannot attain a perfectly uniform bevel width it would still be more even than before. I am embedding an image from another BladeForums thread for reference, the specific origin of which I have sadly forgotten. You would want to create the situation shown in the third image from the top, where the marker is being removed from the shoulder of the flat and the apex at the tip, so you would reverse the correction given in that frame and reposition with the tip CLOSER to the clamp.
I do not recommend that you attempt the differential edge angle before, without, or as part of the correction proposed in the third paragraph of this post. The reason is that making the angle more obtuse will initially narrow the bevel on which you are grinding, until the grinding reaches the shoulder of the existing bevel. This in my opinion will make keeping any sense of how the edge is centered difficult. If after performing the centering correction you choose to apply a more obtuse angle near the tip you can count strokes on each side to keep it centered.
*An assumption, but not without basis.
On many knives the edge thickness increases as you approach the tip, as the edge moves up toward the spine into the thicker part of the stock. This is countered by the primary blade grind also sweeping upward but typically not at the same rate as the edge. This keeps the tip of the knife stronger—good insurance for most production knives—but it creates a complication for sharpening. If you want keep the edge bevel angle the same throughout then necessarily the bevel will be wider in this thicker area. Conversely if you wish to keep the same width of bevel throughout then necessarily the edge must be at a more obtuse angle in this thicker area.
It appears to me that you ground the right side of the knife to produce an even bevel width, then ground the left side in order to finish the apex. The tip region, being thicker behind the edge,* required more grinding which resulted in a wider bevel there. To correct this you would grind only on the right side near the tip, taking care to progressively blend this back through the belly of the knife. This will widen the bevel on the right side in that area, while narrowing it on the left. When complete the bevels on both sides will still be wider at tip than the rest of blade, especially since you have taken off some extra material near the tip, making the behind-the-edge thickness greater. There is nothing wrong with this but it may not be the look you desire. If you do fine cutting with the tip I encourage you to accept this look and enjoy the improved cutting performance of a lower angle edge.
If you desire an even bevel width from heel to tip then you must change the sharpening angle along the length of the edge, with understanding that this will reduce the fine cutting performance near the tip. In a clamped system this is done by the position of the blade in the clamp. Since I do not use a clamped system myself I am not practically familiar with the amount of angle-change heel-to-tip that is readily produced. Nevertheless even if you cannot attain a perfectly uniform bevel width it would still be more even than before. I am embedding an image from another BladeForums thread for reference, the specific origin of which I have sadly forgotten. You would want to create the situation shown in the third image from the top, where the marker is being removed from the shoulder of the flat and the apex at the tip, so you would reverse the correction given in that frame and reposition with the tip CLOSER to the clamp.
I do not recommend that you attempt the differential edge angle before, without, or as part of the correction proposed in the third paragraph of this post. The reason is that making the angle more obtuse will initially narrow the bevel on which you are grinding, until the grinding reaches the shoulder of the existing bevel. This in my opinion will make keeping any sense of how the edge is centered difficult. If after performing the centering correction you choose to apply a more obtuse angle near the tip you can count strokes on each side to keep it centered.
*An assumption, but not without basis.
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Your explanation makes a lot of sense, thank you for taking the time to walk me through it.I was trying to check for errors in the blade grind from the manufacturer. I cannot be certain without examining it myself, but I cannot see any so I will assume that the asymmetry is due to the edge grind.
On many knives the edge thickness increases as you approach the tip, as the edge moves up toward the spine into the thicker part of the stock. This countered by the primary blade grind also sweeping upward but typically not at the same rate as the edge. This keeps the tip of the knife stronger—good insurance for most production knives—but it creates a complication for sharpening. If you want keep the edge bevel angle the same throughout then necessarily the bevel will be wider in this thicker area. Conversely if you wish to keep the same width of bevel throughout then necessarily the edge must be at a more obtuse angle in this thicker area.
It appears to me that you ground the right side of the knife to produce an even bevel width, then ground the left side in order to finish the apex. The tip region, being thicker behind the edge,* required more grinding which resulted in a wider bevel there. To correct this you would grind only on the right side near the tip, taking care to progressively blend this back through the belly of the knife. This will widen the bevel on the right side in that area, while narrowing it on the left. When complete the bevels on both sides will still be wider at tip than the rest of blade, especially since you have taken off some extra material near the tip, making the behind-the-edge thickness greater. There is nothing wrong with this but it may not be the look you desire. If you do fine cutting with the tip I encourage you to accept this look and enjoy the improved cutting performance of a lower angle edge.
If you desire an even bevel width from heel to tip then you must change the sharpening angle along the length of the edge, with understanding that this will reduce the fine cutting performance near the tip. In a clamped system this is done by the position of the blade in the clamp. Since I do not use a clamped system myself I am not practically familiar with the amount of angle-change heel-to-tip that is readily produced. Nevertheless even if you cannot attain a perfectly uniform bevel width it would still be more even than before. I am embedding an image from another BladeForums thread for reference, the specific origin of which I have sadly forgotten. You would want to create the situation shown in the third image from the top, where the marker is being removed from the shoulder of the flat and the apex at the tip, so you would reverse the correction given in that frame and reposition with the tip CLOSER to the clamp.
I do not recommend that you attempt the differential edge angle before, without, or as part of the correction proposed in the third paragraph of this post. The reason is that making the angle more obtuse will initially narrow the bevel on which you are grinding, until the grinding reaches the shoulder of the existing bevel. This in my opinion will make keeping any sense of how the edge is centered difficult. If after performing the centering correction you choose to apply a more obtuse angle near the tip you can count strokes on each side to keep it centered.
*An assumption, but not without basis.