When is time to change a knife or reshape the bevel?

[WolfY]

Today's chef's knives are shaped as triangle with straight or little concave face. I guess some of the reasons this shape is popular is easier production and less effort to cut.
As we grind them the edge is creeping up and the meeting point of the bevel and edge is widening a little.
When is the time to either reshape the bevel or buy new knife?

Attached is an illustration of sharpening out 9mm from the original 40 showing how the meeting point of the edge and bevel are changed from 0.85mm to 1.2mm. By the way I used bevel of 1dgr on each side.

What is your opinion/ thoughts?

[Jan]

Recently I have attached link to Victorinox guidance for re-shaping their knives. I think it may be useful for your considerations. 

https://assets.victorinox.com/medias/servive-cut-drinding-sharpening-en-nov2012.pdf?context=bWFzdGVyfGN1dHwxNzIyNzd8YXBwbGljYXRpb24vcGRmfGg1MC9oZWUvODc5ODIzOTM1OTAwNi5wZGZ8ZGJmOGVkMGRlODEzMGExYTY3Mjc4Y2U0ZmI3NmIwMzAwZjEwZmM1MzIzOWFmYjhjYzE3NTE0NTU0YTk3ZWRlNw

Jan

[Ken S]

Excellent topic, WolfY, and excellent reply, Jan.

I do not have a good answer for this. It is a relevant question for Tormek knife sharpeners and one for which we will soon have some guidance from Sweden.

Ken

[stevebot]

John Juranitch says that knives should be .020" (0.5mm) a quarter inch back from the edge. This jives with the Victorinix 0.4 to 0.6 mm, although they do not say how far back is considered "the edge"

[Ken S]

Steve, I believe you have discussed this before, however, for the benefit of the forum, would you please discuss what you would do if a customer asked you to sharpen a knife which needed thinning?

Ken

[WolfY]

Made this case study.

[WolfY]

According to Victorinox with this case study parameters we have about 3.7mm before having to grind the bevel in order to keep the knife with similar characteristics as origin. Interesting.

And tanks Jan for the PDF. It really helped.

[Jan]

John Juranitch says that knives should be .020" (0.5mm) a quarter inch back from the edge. This jives with the Victorinix 0.4 to 0.6 mm, although they do not say how far back is considered "the edge"

Steve,

thanks for mentioning John Juranitch. 

Attached there is the relevant section of his famous article.

From his sketch we can derive that the angle of the tapered blade is circa 9° which is much more than we can see at modern kitchen knives. My older Solingen boning knife has the angle of the blade some 6° ("relief" in Juranitch terminology).

Jan

[Ken S]

Thanks for posting the article, Jan. I put it in ibooks on my ipad.

Ken

[stevebot]

Here is the full article
http://sharpeningmadeeasy.com/Juranitch1977Feb.htm

[Jan]

Steve, I believe you have discussed this before, however, for the benefit of the forum, would you please discuss what you would do if a customer asked you to sharpen a knife which needed thinning?

Ken

Ken,

this is tricky question. We know well how to sharpen an edge angle but not how to ground a defined thickness in a certain distance from the edge. 

Jan

[Jan]

Here is the full article
http://sharpeningmadeeasy.com/Juranitch1977Feb.htm

Juranitch is known supporter of dry honing. For me the figure from his article in Popular Science is not fully convincing.

https://photos-4.dropbox.com/t/2/AAC0D36HZhtlopMJkoBsGO94JKlJd98ywvwMk4qpM3fSdQ/12/484370172/jpeg/32x32/1/_/1/2/Jurantich_oil_vs_dry_honing.jpg/EOiO4vYDGF8gBygH/vBFdxnuS_KcwB8kg4JQOcM-656bBpJ_bXv3R7Ki0nRw?size=1600x1200&size_mode=3

Jan

[Ken S]

Jan,

I agree the issue of knife thinning is tricky. I certainly would not feel comfortable doing it. It is, however, an issue knife sharpeners must occasionally confront. As much as I value the handbook, there are certain important things it does not cover. This is one of those things.

If the design of the Tormek is capable of thinning, we should know about that technique. Those of us who are willing to learn that skill will do so.

If the design parameters of the Tormek do not include knife thinning, and that operation should be left to more specialized machinery, the handbook should state that. Every machine has its parameters.

Ken

[Jan]

Ken,
I agree with you. 

Fortunately hollow ground blades only seldom need blade thinning, because their thickness slowly increases with the distance from the cutting edge. When necessary, thinning can be done on Tormek by applying a patient step by step procedure with very small material removal in one step followed by thickness measurement.

The need to thin the blade is more frequent by V ground blades (e.g. butcher's knives) because their thickness more rapidly increases with the distance from the cutting edge. This can be done on the side of the grinding wheel, freehand or supported by the tool rest or some homemade platform.

Thinning of convex ground blades (e.g. cleavers) using Tormek is for me hardly imaginable. 

Jan

[Ken S]

Jan,

My point is that either thinning is or is not a function which can or should be performed with the Tormek. If this is a Tormek compatable function, I would like to see it described in the handbook. If it is not, I would like to see this advised in the handbook. Every tool has functions it perform well, some functions doable but not in the primary design, and some functions which are not practical or possible. I would like to see this discussed in future editions of the handbook and posted on the forum for present use.

Ken