Tutorial on how to thin european knives

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GeneParmesan

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Here I want to share my rough procedure on how I thin my european chef knives.
This is a rework of a post that I made a while ago in a german community.

In this context please note that one other user there also posted another, very good, description on the same process with diamond stones

The goal of this process is to achievea geometry of european knive that does not suck but still is stable. I.e. I am aiming at a flat, convex grind with a small primary bevel with an angle of 18 degrees remaining.
I usually aim for a thickness of around 0,2 mm 3mm above the cutting edge.
With this geometry it is possible to cut carrots and potatoes without cracking while maintaining a geometry that is still stable enough to give the knive to my girlfriend.

After this process, I keep the knives sharp with a Dick Micro Sharpening Steel and a Dick Polished steel until sharpenng with a stone is required.

The reason for thinning european knives instead of using japanese knives that are thin out of the box are the following:
- Knives with a hardness of up to ~60 HRC can be kept sharp with a sharpening steel. I prefer reqular honning to the use of l
- Also I like the overall design of many european knives.
P1010012.JPG

(Some examples of thinned knifes)

The overall process is the following:

- Resharpening and polishing the primary bevel
- Thinning the edges of the knive and setting the convex grind
- Setting a micro phase/repairing the old primary bevel


Resharpening and polishing the primary bevel:
First I add a primary bevel of 18 to 20 degrees (or 36 to 40 if you will) with a sharpening rig to the knive.
The reason for this is that I want to assure that the angle of the knive is consistent throughout the whole length of the blade.
Also if there are any defects with the knive, like an overgrind or small chips, now is the time to fix that.
Then I polish the primary bevel with a stone of 3000 to 4000 grid JIS.
This is an important step because in the next step the reflection of the polished primary edge can be used to determine the overall progress.
The reason for this is that the reflection of the polished edge is clearly distinct from the scratch pattern of your thinning device.

Giving the knive a convex grind:
After the initial preparations I thin the edges of the knive and give it a convex grind.

While taking material away of the edges I regularly check the progress of the thinning. For this I use the reflection of the primary bevel to determine how thick the knive is now above the primary bevel. Furthermore I check with a vernier calliper how far from the cutting edge the points are where the blade has a thickness of around 0,2mm.
P1030430.jpg

(The knive, during the process)
P1030428.jpg

(The area around the cutting edge, during the process)

I usually stop just before a burr forms, i.e. when the remaining primary bevel has become thin like a hair. I am also aiming for the knive having a thickness of 0,2 to 0,25mm 3mm above the cutting edge.
P1030443.jpg

(The knive, when I finish)
P1030437.jpg

(The area around the cutting edge, when I finish)

The thinning of the knive can be done with different tools:
Sandpaper on a mousepad or a fex layers of cleaning cloth:
P1030434.jpg

(The aproximate angle I keep during the thinning)
I try to keep a very flat angle, i.e. so the top of the knive is only 1 to 2 mm above the sandpaper. The padding below the sandpaper will take care of the convex grind. This gives me the most flat grind of all of the method and is also the most forgiving and requires the least concentration (you can easily listen to a TV series while you do your thing). It also takes the most time, though.

A diamond plate:
Instead of keeping a contant angle I try to vary the angle slightly while moving forward and backward. If I am close to the grip of a european chef knives (i.e. where the height of the blade is between 40 and 50mm) I vary the height between 1 and 4mm during my movements. The speed of this method is relatively fast. It is harder to use than the other methods because you have to take care of the convex pattern on your own. If I find that the thinning with the sandpaper left a grind that is to convex due to the padding being to soft I correct this error with a diamond plate.
Don't use new diamond plates for this due to their irregular scratch pattern. Especially if your knive is getting thinner in the area around the cutting edge it can become hard to remove irregular deep scratches. The worst case that could happen in this context is that the scratches are so deep that you have to reset the cutting edge.

A slow running belt grinder like the work sharp in the Ken Onion edition:
Here I either add stabilising cloth under the belt ( kind of risky, but it works) or I try to grind close to one of the wheels. I eyeball the angle, but similar to the other methods I try to stay as flat as possible. Depending on the slope of the belt, this gives a move pronounced convex grind.
Although I am using a belt grinder that is not cooled I am not scared of descroying the temper in the first fex micro meters behind the cutting edge because I add a micro bevel after this step and therefore remove the potentially damaged material anyways.
The speed advantage compared to the other methods is not that large as I hoped. Although I am not scared of having a handwarm cutting edge, I don't want to get a piping hot blade either. Therefore I regularly stop to let the knive cool down, again.
Depending on the slope of the belt this method gives a rather pronounced convex grind. This must not be a bad thing, though. In my experience it is sufficient to thin most knives in the first 5 to 10mm behind the cutting edge to greatly improve the cutting performance of a knive.

In generall I avoid sand paper and belts with a grid below 120. If the grid is lower the scratch pattern often is so intensive that it becomes very hard to determine the overall progress depending on the old primary bevel.

Setting a new primary bevel:
After I've thinned my knive to my likings I add new primary bevel with an angle between 18 and 20 degrees.
I usually do this with either a 1000 or 4000 grid. Please be carefull when doing so and apply only very little pressure. Because the knive now is much thinner then before you will now remove material much quicker when applying the same pressure.
P1010016.JPG

(The knive, after setting of the micro bevel)
P1010014.JPG

(The area around the cutting edge, after setting the micro bevel)

If you have any more questions, please feel free to ask.
 

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