A guy showed me his knife the other day. He had clearly sharpened it on a guided system, but it wasn't that sharp. I cleaned it up for him and in the process made an observation that I have been thinking about since then. I realized what the problem likely was and will tell him next time I see him.
But I had some more general thoughts as well and figured I'd share.
Why your knife isn't sharp even after you sharpened it.
1. The angle of the knife to the sharpening media is too inconsistent. It doesn't have to be perfect, but it can't vary too much. The more consistent the better. A guided system avoids this pitfall. It's also worth noting that dished/worn stones make holding a consistent angle nearly impossible. If you have a dished stone, either get rid of it or use a flattening stone to clean it up and flatten the sharpening surface.
2. The knife wasn't sharpened sufficiently. No matter how consistent the angle is to the stone, enough metal has to be removed to reach all the way down the side of the knife to where the new edge will be. Think of the knife as a rod instead of a mostly flat piece of metal. You need to grind off enough metal on both sides of the rod at an angle so that the bevels meet and a point is formed all down one edge of the rod. If you don't do that, the knife won't be sharp, no matter how perfect your technique is. Learning to detect a burr will allow you to verify that you've removed enough metal to form a good apex.
3. Too much pressure was used during the final stage of sharpening. The first step of sharpening is to remove metal to form an edge. It's acceptable (not really necessary, but acceptable) to use significant pressure during this phase. It also requires fairly coarse grit since you need to remove significant amounts of metal. The second stage of sharpening is "finishing" the edge. This works best with fine grit sharpening media and REQUIRES light pressure. The edge is already formed at this stage and it's a wispy thin piece of metal. If you push it hard against the sharpening media it will bend or break off. For this stage you can pretty much use only the weight of your hand and the knife--you don't really need to push down at all.
You can get a rough edge that will be of workable sharpness, but it won't be razor sharp unless you go to much lighter pressure and to finer media for the "finishing" stage.
If you are using a good quality guided system with graduated grits and still can't get your knife razor sharp, #2 or #3 is the problem.
Very quick instructions for sharpening with the above information in mind.
1. Using coarse grit media and a consistent angle, grind the knife until a burr is formed all along the opposite side of the edge from the side in contact with the media.
2. Repeat on the other side. Step 1 and 2 will take most of your time sharpening. Maybe 3/4 or more of the overall time and effort.
3. Do a few alternating light pressure passes with the coarse grit media from step one on each side to clear the burr. This pass needs to move the knife forward across the sharpening media as if the sharpening media is being carved. Angle is critical as you just want to remove the burr without altering the angle of the new bevel formed in the earlier steps. You shouldn't be able to detect any trace of a burr on either side of the edge now.
4. Switch to a fine grit and from this point on use only very light pressure and alternating strokes with the knife moving forward across the media as if carving it. Angle is critical here as you want to polish the bevel of the edge and don't want to try to alter that bevel angle at all. If you are "afraid" of the edge, you will place the knife at a shallower angle and polish only the upper part of the bevel without polishing all the way to the edge. If you get too aggressive, you will place the knife at too steep an angle (compared to the earlier steps) and effectively dull the edge.
If you want to shorten step 4, you can intentionally steepen the angle very slightly compared to the earlier steps and just do a few alternating passes with very light pressure. This will polish only a "sub-bevel" right at the apex which means it can be done much faster than polishing the entire bevel. Really keep the pressure light (Yes, I keep saying that. No, I'm not over-emphasizing it.) as you are pushing the edge against the media and it only takes a very little pressure to deform such a thin piece of metal.
When you are learning step 4, check for a burr frequently, maybe after every pair of alternating passes. It will be much harder to detect than when using a coarse grit media. If you find one, you screwed up step 4 and you need to go back and do steps 1, 2 and 3. They will go a lot faster this time since the bevel is already formed and you just need to take a tiny bit more off each side to get rid of the damage to the edge from using the wrong angle or too much pressure in step 4.
Then be more careful with pressure and angle when you start step 4 again.
The knife I mentioned in the opening paragraph of this post had a very small but consistent burr all down one side. The guy was using too much pressure on his guided sharpener (and probably not alternating sides) when he was finishing the edge and that pressure was deforming the metal slightly.
But I had some more general thoughts as well and figured I'd share.
Why your knife isn't sharp even after you sharpened it.
1. The angle of the knife to the sharpening media is too inconsistent. It doesn't have to be perfect, but it can't vary too much. The more consistent the better. A guided system avoids this pitfall. It's also worth noting that dished/worn stones make holding a consistent angle nearly impossible. If you have a dished stone, either get rid of it or use a flattening stone to clean it up and flatten the sharpening surface.
2. The knife wasn't sharpened sufficiently. No matter how consistent the angle is to the stone, enough metal has to be removed to reach all the way down the side of the knife to where the new edge will be. Think of the knife as a rod instead of a mostly flat piece of metal. You need to grind off enough metal on both sides of the rod at an angle so that the bevels meet and a point is formed all down one edge of the rod. If you don't do that, the knife won't be sharp, no matter how perfect your technique is. Learning to detect a burr will allow you to verify that you've removed enough metal to form a good apex.
3. Too much pressure was used during the final stage of sharpening. The first step of sharpening is to remove metal to form an edge. It's acceptable (not really necessary, but acceptable) to use significant pressure during this phase. It also requires fairly coarse grit since you need to remove significant amounts of metal. The second stage of sharpening is "finishing" the edge. This works best with fine grit sharpening media and REQUIRES light pressure. The edge is already formed at this stage and it's a wispy thin piece of metal. If you push it hard against the sharpening media it will bend or break off. For this stage you can pretty much use only the weight of your hand and the knife--you don't really need to push down at all.
You can get a rough edge that will be of workable sharpness, but it won't be razor sharp unless you go to much lighter pressure and to finer media for the "finishing" stage.
If you are using a good quality guided system with graduated grits and still can't get your knife razor sharp, #2 or #3 is the problem.
Very quick instructions for sharpening with the above information in mind.
1. Using coarse grit media and a consistent angle, grind the knife until a burr is formed all along the opposite side of the edge from the side in contact with the media.
2. Repeat on the other side. Step 1 and 2 will take most of your time sharpening. Maybe 3/4 or more of the overall time and effort.
3. Do a few alternating light pressure passes with the coarse grit media from step one on each side to clear the burr. This pass needs to move the knife forward across the sharpening media as if the sharpening media is being carved. Angle is critical as you just want to remove the burr without altering the angle of the new bevel formed in the earlier steps. You shouldn't be able to detect any trace of a burr on either side of the edge now.
4. Switch to a fine grit and from this point on use only very light pressure and alternating strokes with the knife moving forward across the media as if carving it. Angle is critical here as you want to polish the bevel of the edge and don't want to try to alter that bevel angle at all. If you are "afraid" of the edge, you will place the knife at a shallower angle and polish only the upper part of the bevel without polishing all the way to the edge. If you get too aggressive, you will place the knife at too steep an angle (compared to the earlier steps) and effectively dull the edge.
If you want to shorten step 4, you can intentionally steepen the angle very slightly compared to the earlier steps and just do a few alternating passes with very light pressure. This will polish only a "sub-bevel" right at the apex which means it can be done much faster than polishing the entire bevel. Really keep the pressure light (Yes, I keep saying that. No, I'm not over-emphasizing it.) as you are pushing the edge against the media and it only takes a very little pressure to deform such a thin piece of metal.
When you are learning step 4, check for a burr frequently, maybe after every pair of alternating passes. It will be much harder to detect than when using a coarse grit media. If you find one, you screwed up step 4 and you need to go back and do steps 1, 2 and 3. They will go a lot faster this time since the bevel is already formed and you just need to take a tiny bit more off each side to get rid of the damage to the edge from using the wrong angle or too much pressure in step 4.
Then be more careful with pressure and angle when you start step 4 again.
The knife I mentioned in the opening paragraph of this post had a very small but consistent burr all down one side. The guy was using too much pressure on his guided sharpener (and probably not alternating sides) when he was finishing the edge and that pressure was deforming the metal slightly.
