Is it possible to thin a knife on a sharpening system ??

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Jeff

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I an curious if anyone has a method to thin a knife on a sharpening system?

Or is it something that is a freehand thing?

I have access to numerous systems:

WickedEdge
TSProf K03
EdgePro
Tormek

None seem appropriate for thinning. Thoughts?

Thanks!
 
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The Tormek might be an exception but the others are quite similar in concept as is the KME I have used quite a lot.

Appropriate for thinning? I say no. Yes, there are ways to drop the angle and get some thinning effects but it just won't be the same as on stones. Especially since you can't alter your angle for the blade profile. You're also dealing with thin (width) stones so what work you do accomplish will be much slower.

Do you have a physical need that requires using a system?
 
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I have the K03, but I'll be darned if I know how to get it down to the ridiculously low angles used for thinning. Even with fillet clamps.

Even if it could, it feels like the wrong tool. It excels at doing very precise angles, but thinning doesn't really call for that.
 

Jeff

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The Tormek might be an exception but the others are quite similar in concept as is the KME I have used quite a lot.

Appropriate for thinning? I say no. Yes, there are ways to drop the angle and get some thinning effects but it just won't be the same as on stones. Especially since you can't alter your angle for the blade profile. You're also dealing with thin (width) stones so what work you do accomplish will be much slower.

Do you have a physical need that requires using a system?

I have no condition requiring that I use a system other than a lack of skill/muscle memory on my stones.

I agree with your assessment of the systems. IMHO TORMEK is even less appropriate for thinning.

I’m just concerned about really scratching the sides of the blade on the stone when I am trying to get a low enough angle to thin a blade.

I guess I will try on some less expensive knives.
 

Jeff

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I have the K03, but I'll be darned if I know how to get it down to the ridiculously low angles used for thinning. Even with fillet clamps.

Even if it could, it feels like the wrong tool. It excels at doing very precise angles, but thinning doesn't really call for that.
[/QUOTE

That was my conclusion as well.

I guess I will have to up my free-hand game!
 

Nemo

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I feel compelled to point out that if you thin with a guided angle system, you will be cutting a new relief bevel into the knife. This will modify the geometry and will therefore modify the knife's behaviour in food.

Why not thin by laying the knife flat on the stones and following the original geometry of the knife? Just remember that most of the steel is removed under where you apply pressure to the blade while sharpening. If you put pressure just behind the edge, you will remove steel in the first cm or two behind the edge.

Just be sure to stop just before (or just as) you hit the edge with your thinning bevel.
 

Pie

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I have no condition requiring that I use a system other than a lack of skill/muscle memory on my stones.

I agree with your assessment of the systems. IMHO TORMEK is even less appropriate for thinning.

I’m just concerned about really scratching the sides of the blade on the stone when I am trying to get a low enough angle to thin a blade.

I guess I will try on some less expensive knives.

If cosmetic damage is the concern, you could tape up the parts that you don’t want to scratch.
 

Benuser

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If cosmetic damage is the concern, you could tape up the parts that you don’t want to scratch.
... or use the long side of the stone.
20220317_093825.jpg
 

TB_London

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Thinning will need refinishing after if you want it pretty.

Decent Sandpaper cut into strips wrapped round a bit of wood and lengthwise strokes can be used if it’s not a lot.

If it needs a lot of thinning get a cheapo and try using the side of the tormek wheel similar to how the advise you lap the back of a chisel. Won’t be quick but fairly controllable
 
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The old hapstone system I use can get down to 5ish degrees but the knife still needs refinished after
 
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I have no condition requiring that I use a system other than a lack of skill/muscle memory on my stones.

I agree with your assessment of the systems. IMHO TORMEK is even less appropriate for thinning.

I’m just concerned about really scratching the sides of the blade on the stone when I am trying to get a low enough angle to thin a blade.

I guess I will try on some less expensive knives.

Also consider trying out the motions on a higher grit stone. It won't actually be thinning but you might get a feel for things with less risk.
 

kayman67

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Yes, with TSProf K03 and EdgePro. But not as you imagine, using the system as it is. You need to make a new holder/stand and level the knife as needed. Because the angles are of no concern, you can set it as high as possible. You raise and position your blade as needed so the plate travels the way it's needed, using the new holder/stand.
 

Desert Rat

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If cosmetic damage is the concern, you could tape up the parts that you don’t want to scratch.
I have used two or three layers of electrical tape on the spine. It worked well for me and for what I started out to accomplish.
 

Jeff

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I feel compelled to point out that if you thin with a guided angle system, you will be cutting a new relief bevel into the knife. This will modify the geometry and will therefore modify the knife's behaviour in food.

Why not thin by laying the knife flat on the stones and following the original geometry of the knife? Just remember that most of the steel is removed under where you apply pressure to the blade while sharpening. If you put pressure just behind the edge, you will remove steel in the first cm or two behind the edge.

Just be sure to stop just before (or just as) you hit the edge with your thinning bevel.


“… lay it flat …” I want to thin (behind the edge) Not the thickness of the entire blade.
 

Jeff

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I have used two or three layers of electrical tape on the spine. It worked well for me and for what I started out to accomplish.
I feel compelled to point out that if you thin with a guided angle system, you will be cutting a new relief bevel into the knife. This will modify the geometry and will therefore modify the knife's behaviour in food.

Why not thin by laying the knife flat on the stones and following the original geometry of the knife? Just remember that most of the steel is removed under where you apply pressure to the blade while sharpening. If you put pressure just behind the edge, you will remove steel in the first cm or two behind the edge.

Just be sure to stop just before (or just as) you hit the edge with your thinning bevel.

Oops .. I forgot to include my additional inquiry …

You lost me when you spoke of cutting a new relief bevel in the knife. ??

NOTE: I can get a full 7.25” x 2.5” stone on the TSProf so that helps a little.
 

kayman67

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“… lay it flat …” I want to thin (behind the edge) Not the thickness of the entire blade.

Same concept, but you would have 2 issues. Lack of reach and lack of movement. Maybe if you would have the convex add-on (not sure if something like is available for any system) and a long enough rod to cover the entire blade.

Just pick up the plate and imagine how would you want it to move to get the results you desire. That's what you need to do to get it working.
 

Nemo

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“… lay it flat …” I want to thin (behind the edge) Not the thickness of the entire blade.

You lost me when you spoke of cutting a new relief bevel in the knife. ??

These are related concepts.

Note that most blades do not have a fully flat grind from (just behind) the edge to the spine.

Some knives are flat part way up the blade face (in fact, these are often very slightly concave because they are usually ground on a large radius circular stone). These knives are often wide- bevelled knives. The blade face above the wide bevel is usually pretty flat (but not quite flat enough to be polished on a stone, unfortunately).

Some knives have a convex grind. Once again, this is often in the bottom part of the blade face, with the part closer to the spine being pretty flat. These knives can be wide-bevelled but often are not. Other knives have a concave grind or even a compound grind such as an s-grind.

Let's take the example of a flat ground wide bevel with the wide bevel forming a 3 degree relief bevel. if you "thin behind the edge" at an angle greater than than the wide bevel's angle (say, 7 degrees), you will be cutting a new 7 degree bevel in between the wide bevel and the edge bevel. This is pretty much the same as "knocking the shoulders off" the bevel. It will likely improve performance if the knife has become thick behind the edge but it won't maintain the knife's original geometry, so how it performs in food will change somewhat.

If you want to maintain the knife's original geometry, you want to remove metal evenly from the whole wide bevel until just before the wide bevel reaches a zero grind.

I have used a flat ground wide bevel as the example here because it is the simplest to understand. However the principal is the same for other grinds: if you want to maintain the original geometry, you must remove metal evenly from the whole relief bevel (blade road). This will obviously require some kind of refinishing afterward for some blades. For convex blades, this requires a kind of modified hamiguriba sharpening. For concave blades, it's difficult to maintain the concavity in home use, so they gradually become flat grinds. Compound grinds are difficult to maintain in this fashion.

As for "laying the blade flat" on the stone, what I mean is that if you lay the blade flat on the stone, then place pressure just above the edge, the blade will realign so that the relief bevel (wide bevel in the example of our flat ground wide bevel) is flat on the stone and steel will be removed from the relief bevel only (and not above it).

The technique for a convex blade is a little more complex but still in involves laying the blade flat on the stone.

You certainly can maintain a knife by knocking the shoulders off at, say, 7 degrees per side and it will almost certainly improve performance over not thinning the knife. However, it will gradually change the geometry of the knife.
 
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Jeff

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These are related concepts.

Note that most blades do not have a fully flat grind from (just behind) the edge to the spine.

Some knives are flat part way up the blade face (in fact, these are often very slightly concave because they are usually ground on a large radius circular stone). These knives are often wide- bevelled knives. The blade face above the wide bevel is usually pretty flat (but not quite flat enough to be polished on a stone, unfortunately).

Some knives have a convex grind. Once again, this is often in the bottom part of the blade face, with the part closer to the spine being pretty flat. These knives can be wide-bevelled but often are not. Other knives have a concave grind or even a compound grind such as an s-grind.

Let's take the example of a flat ground wide bevel with the wide bevel forming a 3 degree relief bevel. if you "thin behind the edge" at an angle greater than than the wide bevel's angle (say, 7 degrees), you will be cutting a new 7 degree bevel in between the wide bevel and the edge bevel. This is pretty much the same as "knocking the shoulders off" the bevel. It will likely improve performance if the knife has become thick behind the edge but it won't maintain the knife's original geometry, so how it performs in food will change somewhat.

If you want to maintain the knife's original geometry, you want to remove metal evenly from the whole wide bevel until just before the wide bevel reaches a zero grind.

I have used a flat ground wide bevel as the example here because it is the simplest to understand. However the principal is the same for other grinds: if you want to maintain the original geometry, you must remove metal evenly from the whole relief bevel (blade road). This will obviously require some kind of refinishing afterward for some blades. For convex blades, this requires a kind of modified hamiguriba sharpening. For concave blades, it's difficult to maintain the concavity in home use, so they gradually become flat grinds. Compound grinds are difficult to maintain in this fashion.

As for "laying the blade flat" on the stone, what I mean is that if you lay the blade flat on the stone, then place pressure just above the edge, the blade will realign so that the relief bevel (wide bevel in the example of our flat ground wide bevel) is flat on the stone and steel will be removed from the relief bevel only (and not above it).

The technique for a convex blade is a little more complex but still in involves laying the blade flat on the stone.

You certainly can maintain a knife by knocking the shoulders off at, say, 7 degrees per side and it will almost certainly improve performance over not thinning the knife. However, it will gradually change the geometry of the knife.


WOW!

Thank you so much for the amazing explanation. The time & effort you invested in sharing this is certainly appreciated!

The more I learn the more I realize how complicated it is and how little I know!

It is a fun journey blending art, science & math to craft a cutting tool!

Thanks. I’m going to print & save your post as a reference.
 
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