Newbie question: chef knive has a negative curve, what to do?

[MarthaH]

Hi everybody,

after decades of using a Lansky sharpening system with more or less success I recently bought a dirty, but not much used Tormek 1200. It sat for a long time in a box with a lot of accessories. It ran, but after 10min the motor lost power. Since the Tormek construction is more than simple, the problem was easily identified: dead motor condensator. After replacing it, the machine is running fine.

Over the time I gathered quite a collection of kitchen knives. One of them, a Zwilling chef knive (20cm) is quite worn. The heel (is this the correct terminus technicus?) is longer than the blade, giving the knive a negative curve at the end.

What would be the correct procedure to repair this?

PS. English is not my native language, please be tolerant ;-)

[Dan]

Hello and welcome to the forum.
Is the blade worn something like this?
https://c8.alamy.com/comp/BPWKJC/an-old-chefs-knife-which-has-been-sharpened-until-the-blade-is-worn-BPWKJC.jpg
It would be useful to see a photo of your knife to be able to advise you better.
"A picture is worth a thousand words" as they say...

Danny

[RickKrung]

Hello and welcome to the forum.
Is the blade worn something like this?
https://c8.alamy.com/comp/BPWKJC/an-old-chefs-knife-which-has-been-sharpened-until-the-blade-is-worn-BPWKJC.jpg
It would be useful to see a photo of your knife to be able to advise you better.
"A picture is worth a thousand words" as they say...

Danny

Yes, or what is sometimes referred to as a "Bird's Beak", like this.

[MarthaH]

Meta question: how can I upload an image? Other forum software allows to upload pics and insert them in a posting. The software asks for an URL, but the pics are one my harddisk?

M.

[HaioPaio]

Have a look here

[MarthaH]

I don't have this options under the entry window, only "Shortcuts: ...". Maybe new members can't upload pics?

Anyway: my knive looks similar to the example in posting #1 from Dan.

[Ken S]

Welcome to the forum, Martha.

If you hold your knife on a cutting board, looking at it from the side, you should not be able to see light under any part of it. If you do, you need to correct it. The area where the light shines through will not cut through properly. In English, we call this "the green onion effect". This is usually caused by the bolster of the knife protruding below the edge of the blade. This is corrected by grinding down the bolster. This should be checked and corrected as part of routine sharpening, although it is frequently overlooked. This can be done freehand. Wolfgang covers this in one of the advanced knife sharpening classes.

Please let us know if this does not correct the problem. We are here to help.

While you are reading this, may I ask a favor? Although I am a US native English speaker, I have some long ago background in Spanish and German. I am sensitive to the frustrations our members who are not native English speakers may have on the forum. The forum has grown from a primarily US based English speaking community to a much more global community. I welcome this growth, although it also brings some "growing pains". I  would welcome any suggestions you might have to make the forum more multilingual friendly. You may post them or send mea Personal Message

[MarthaH]

Welcome to the forum, Martha.

If you hold your knife on a cutting board, looking at it from the side, you should not be able to see light under any part of it.

This implies that the cutting part of blade is straight. Usually it is curved, but I think you want to say it should touch the board at one point only (this being the lowest part of the curve). If you have two points, the blade curves away from the board between the two contact points.

That said, how do I remove the excess of material towards the grip? I found a video on YT where someone repaired a similar knive by grinding away the excess metal with a belt sander before grinding the blade. I don't have a belt sander, can I use the standard (coarse) Tormek stone for this?

M.

PS. I now can add pics, this is the knive I want to sharpen.You cannot view this attachment.

[MarthaH]

While you are reading this, may I ask a favor? Although I am a US native English speaker, I have some long ago background in Spanish and German. I am sensitive to the frustrations our members who are not native English speakers may have on the forum. The forum has grown from a primarily US based English speaking community to a much more global community. I welcome this growth, although it also brings some "growing pains". I  would welcome any suggestions you might have to make the forum more multilingual friendly. You may post them or send mea Personal Message

I've been around discussion boards from the early days of the internet (usenet...) until today (I got my first permanent (!) connection from my home to the net in 1995, with superfast 64kb/s...) English is by now the "lingua franca", and nearly everybody (with some technical background) is more or less fluent in it. My native language is German, and there are german speaking boards about knives and grinding them. However, I feel discussions there tend to turn into esoteric regions with more or less connections to the real live. I read through several threads here and think the contributors here are a little more down to earth. I appreciate this approach ;-)

It is not easy to fill a board with lively discussions in several languages. Anyone who is into a technical/practical hobby like this should at least be able to follow the topics in english, so no direct advice from me. One could however keep a list of native speakers somewhere in this board to have someone to talk to if the language capabilities are not precise enough.

[tgbto]

Martha, welcome to the forum. Your knife exhibits a common issue with Western knives: they often have what is sometimes called a "full bolster".

It is a safety feature intended to prevent the user from nicking their fingers with the heel of the blade. In Japan, where cooks are usually more educated with knife handling, there are usually none. The issue with full bolsters is precisely what you are encountering : it's a PITA when it comes to sharpening, and the gap that gets created hinders cutting.

There are several threads about this, such as this one.

TL/DR : You can reduce the bolster using your Tormek, but it will be time-consuming and will cause increased and uneven wear to your wheel. A belt grinder (preferred) or a bench grinder will make it faster.

Cheers,

Nick.

[BPalv]

Unlike yourself, I started with a belt grinder.  I use mine quite frequently for different needs when sharpening.  I have a 1x30 variable speed Rikon, but there are a ton of different units out there.  They can be pretty inexpensive and would quickly deal with that particular issue you're having.
If you're just sharpening your own knives it may be overkill , but you will find other uses as well.

[RickKrung]

...snip...
That said, how do I remove the excess of material towards the grip? I found a video on YT where someone repaired a similar knive by grinding away the excess metal with a belt sander before grinding the blade. I don't have a belt sander, can I use the standard (coarse) Tormek stone for this?

M.

PS. I now can add pics, this is the knive I want to sharpen.You cannot view this attachment.

Unlike yourself, I started with a belt grinder.  I use mine quite frequently for different needs when sharpening.  I have a 1x30 variable speed Rikon, but there are a ton of different units out there.  They can be pretty inexpensive and would quickly deal with that particular issue you're having.
If you're just sharpening your own knives it may be overkill , but you will find other uses as well.

A belt grinder could be an excellent option, if you do enough sharpening and need the heavier metal removal often enough.  I have two, a Viel 1x42 and now a Vevor 1x30.  I also have diamond and CBN wheels for my T8 and a Rikon slow speed bench grinder.  All cost a good bit (but not nearly as much as a Tormek) and all perform reasonably well. 

One note of caution, belt grinders can generate a lot of heat quickly, so to avoid ruining the temper, I highly recommend one that is variable speed.  I have just recently been using the Vevor 1x30 and it can be slowed to the same low surface speed as the Tormek grinding wheels.  It can also be reversed (through programming steps) to be able to run edge-trailing.  This machined, while running about $200 USD is one of the cheaper options (to diamond and CBN wheels) and is extremely versatile, being usable for general purpose grinding of all sorts of things.  It does generate that annoying grinding grit debris, however. 

However, I think the least expensive and appropriate for the occasional heavy grinding is a traditional high speed grinding wheel mounted/adapted to a Tormek.  There has been a lot of discussion on this forum, since at least 2010 about mounting Norton 3X (blue) grinding wheels of either 64 or 80 grit.

They can be quite aggressive, run in the water bath just like Tormek grinding wheels and trued using the Tormek truing tool.  At 1" width, and (at least in the USA) an arbor hole that requires custom sleeves to adapt to the Tormek 12mm shaft.  Ken S and I have been strong proponents of this method. 

If you do a search here for "Norton" or "Norton 3X" you will find so many posts, it may be difficult to find one specific to actually doing the adaptation.  It likely will require a bushing to adapt the arbor hole and some flange washers to take up space on the shaft, due to the difference in wheel width.  I machined both because I could.  Others have found creative ways, one being 12mm fender washers.  I think someone found an online source for an adapter.  Below is a photo of an 8" Norton 3X mounted on my T8 and another of the bushing and flange washers I machined.  Here is a video of truing a 10" no-name grinding wheel on my T8.