palindrome
Member
I want to share a technique for thinning behind the edge (knocking down the shoulders or making the edge bevel more acute) that I discovered when making a knife from M35, which is so difficult to work that no reasonable knife maker would use it.
I'd say this technique needs some alpha/beta testing, since the final finish still had some scratches, and there's no way to prove the heat stays under control.
The problem
Your blade is too thick behind the edge. This can manifest in an edge bevel that's longer than a mm (which hurts cutting performance and makes sharpening difficult), or an excessively obtuse edge bevel that doesn't cut well--and when you try to set a steeper bevel you end up just sharpening the shoulders, unless you are willing to spend several hours with a stone.
TL;DR
Iteratively grind down the shoulders, and make a more and more acute edge bevel. Do not grind the cutting edge at all, and wet the knife between passes.
The technique
Start by sharpening it at whatever angle feels natural for the blade. If you are making a new blade, it can be as obtuse as you like to save time. The goal is to have a primary bevel around 1 mm.
Use a colored permanent marker or layout fluid to mark the primary bevel. You don't need to mark the whole thing, but it's helpful if you mark the shoulder and it's critical to mark all the way to the edge.
Secure the blade with a clamp or vice so it is horizontal with the edge toward you (tip pointing to the side). Put a fresh (not dished) grinding tip on the dremel. Use a high speed.
Hold the dremel at a near horizontal angle and take metal off of the shoulder. Make passes and always keep the tool moving. I suggest you skip the tip because you are likely to round it off. With each pass, the colored line on the bevel will get narrower. However the coloring at the very edge should never be grinded away! This would mean you are holding the tool wrong and ruining the cutting edge.
After a pass, pour or spray water on the blade. At the very least, wait a few seconds for some of the heat to flow from the grinding region into the rest of the blade. The thinner it gets, the more you need to worry about heat. The lower alloy the steel is, the more you need to worry about heat. (On the other end of the spectrum, you don't need to worry at all if it is a HSS.)
Do as many passes as necessary to get the edge bevel coloring very thin, then flip the knife and do the other side. You are almost at the point of "no bevel", however the knife is still probably not thin behind the edge as you would like.
This image I borrowed shows where the marker (shaded area) will be removed. The lower marker band will get progressively thinner with each pass.
Now start again, making a more acute edge bevel this time. It will become wide again, and you can knock it down with the dremel again. If you don't want a more acute edge bevel, you are done--the blade is as thin behind the edge as you can safely make it. You can refine the blade on whetstones unless it is too hard and requires tools.
Tool selection
The cylinder shape works well; a disc shape would be too difficult. Aluminum oxide would be good, but I found they can't cut hardened steel. A wider head is better than a narrow one because its wider surface contact is less likely to cut a groove.
I used a coarse sanding drum (it was 60 or 80 grit). If it cuts, you will see sparks. If not, you are wasting your time and may overheat the metal. When using a coarse grit, you must keep a perfect angle--if you point downward too much, the scratches in the upper part of the blade will never come out. This happens because the middle of the sanding drum gets dulled from the work, while the top is still fresh and sharp. The top of the drum is capable of cutting much deeper furrows than the middle.
Warnings
First off, this technique can't give perfect evenness. (But if you find a high spot, you can always knock it down later, using a stone or a power tool as you prefer.) Next, the scratch pattern will be in the "wrong" direction. I wonder if there would be high spots that would interfere with using a whetstone on the shoulder. If so, sandpaper (maybe a sanding stick with leather backing) would probably be the way to take care of it.
I would not use a dremel on a knife I considered a work of art. Fortunately, the only way I'm going to own a work of art knife is if I make it. And I'll probably make it with power tools.
I'd say this technique needs some alpha/beta testing, since the final finish still had some scratches, and there's no way to prove the heat stays under control.
The problem
Your blade is too thick behind the edge. This can manifest in an edge bevel that's longer than a mm (which hurts cutting performance and makes sharpening difficult), or an excessively obtuse edge bevel that doesn't cut well--and when you try to set a steeper bevel you end up just sharpening the shoulders, unless you are willing to spend several hours with a stone.
TL;DR
Iteratively grind down the shoulders, and make a more and more acute edge bevel. Do not grind the cutting edge at all, and wet the knife between passes.
The technique
Start by sharpening it at whatever angle feels natural for the blade. If you are making a new blade, it can be as obtuse as you like to save time. The goal is to have a primary bevel around 1 mm.
Use a colored permanent marker or layout fluid to mark the primary bevel. You don't need to mark the whole thing, but it's helpful if you mark the shoulder and it's critical to mark all the way to the edge.
Secure the blade with a clamp or vice so it is horizontal with the edge toward you (tip pointing to the side). Put a fresh (not dished) grinding tip on the dremel. Use a high speed.
Hold the dremel at a near horizontal angle and take metal off of the shoulder. Make passes and always keep the tool moving. I suggest you skip the tip because you are likely to round it off. With each pass, the colored line on the bevel will get narrower. However the coloring at the very edge should never be grinded away! This would mean you are holding the tool wrong and ruining the cutting edge.
After a pass, pour or spray water on the blade. At the very least, wait a few seconds for some of the heat to flow from the grinding region into the rest of the blade. The thinner it gets, the more you need to worry about heat. The lower alloy the steel is, the more you need to worry about heat. (On the other end of the spectrum, you don't need to worry at all if it is a HSS.)
Do as many passes as necessary to get the edge bevel coloring very thin, then flip the knife and do the other side. You are almost at the point of "no bevel", however the knife is still probably not thin behind the edge as you would like.
This image I borrowed shows where the marker (shaded area) will be removed. The lower marker band will get progressively thinner with each pass.
Now start again, making a more acute edge bevel this time. It will become wide again, and you can knock it down with the dremel again. If you don't want a more acute edge bevel, you are done--the blade is as thin behind the edge as you can safely make it. You can refine the blade on whetstones unless it is too hard and requires tools.
Tool selection
The cylinder shape works well; a disc shape would be too difficult. Aluminum oxide would be good, but I found they can't cut hardened steel. A wider head is better than a narrow one because its wider surface contact is less likely to cut a groove.
I used a coarse sanding drum (it was 60 or 80 grit). If it cuts, you will see sparks. If not, you are wasting your time and may overheat the metal. When using a coarse grit, you must keep a perfect angle--if you point downward too much, the scratches in the upper part of the blade will never come out. This happens because the middle of the sanding drum gets dulled from the work, while the top is still fresh and sharp. The top of the drum is capable of cutting much deeper furrows than the middle.
Warnings
First off, this technique can't give perfect evenness. (But if you find a high spot, you can always knock it down later, using a stone or a power tool as you prefer.) Next, the scratch pattern will be in the "wrong" direction. I wonder if there would be high spots that would interfere with using a whetstone on the shoulder. If so, sandpaper (maybe a sanding stick with leather backing) would probably be the way to take care of it.
I would not use a dremel on a knife I considered a work of art. Fortunately, the only way I'm going to own a work of art knife is if I make it. And I'll probably make it with power tools.
Last edited:
