the missing knife test

[Ken S]

I have sharpened two of my kitchen knives (8" chef and 6" slicer) on my Tormek.Both easily caught on my thumbnail and cut paper.

Both failed to function properly on my cutting board.

Ron Hock addresses the problem in his sharpening book.  Leonard Lee and Steve Bottorff do not.  The Tormek Handbook does not include it.  Not even Jeff's otherwise well done knife demo video mentions it.  (Sorry, Jeff.)

The problem is quickly and easily diaganosed.  The knife is held with the cutting edge against the cutting board. The blade is allowed to rock back and forth.  Any light shining through between the edge and the cutting board indicates a hollow spot in the blade.  That part of the blade will not cut completely; things like green onions will not be cut through.

Such a knife will probably be returned to the sharpener as unsatisfactory or taken elsewhere.

The problem is the curve of the blade has been compromised by incorrect sharpening.  This creates the flat or hollow spot.  The bolster may also need to be ground back.

I followed Ron Hock's suggestion of repairing the first knife using a belt grinder.  This method is quite satisfactory.  I repaired the second knife (with less of a problem)using my Tormek.  I am not an experienced knife sharpener.  I consider my Tormek repair to be barely satisfactory and somewhat hit or miss.

I believe the Tormek is capable of handling this problem better in more experienced hands.  I would welcome suggestions.  (A more in depth knife sharpening video would be most welcome.)

I believe mastering this problem is essential for anyone who wishes to sharpen kitchen knives for professionally,  as a restaurant owner, or for a home kitchen.

Please help.

Ken

[Herman Trivilino]

I believe this issue has been discussed in a different context here in the forum.

The general issue, to my way of thinking, is the reshaping of the edge.  This comes up when, for example, the tip of a knife has broken off, or as you mention here in this thread Ken, there's a section of the edge that's concave.

The easiest way to fix it is to reshape the edge by grinding at an edge angle of 90^o in the places where it's needed.  Then sharpen as usual.

The other comment I have is that the problem you mention, Ken, may not be noticed by people who use a slicing motion rather than a rocking motion.  As I recall Ron Hock mentions this, too, in his book.

[Ken S]

Herman, I will check my copy of Ron Hock's book about slicing instead of rocking.

I did a forum search of "broken tip".  The only post which popped up was your last response.  My point was that the solution to the blade curve problem shouldn't be something buried in a somewhat related post which does not emerge from a simple search.  The Tormek related media make knife sharpening look like zip zip, and you're done.  That's true with a new knife or with one which has been very carefully sharpened in the past.  That leaves a lot of unprotected territory.  If the Tormek is designed and marketed as a tool for the sharpening professional, and I believe it is, than the training should cover such things.

This post is mostly an extension of my belief that Tormek manufactures a fine product, but does not fully support the purchasers with proper training options.  From time to time, we read posts by new or prospective buyers who plan to start a sharpening business.  Someone who sharpens kitchen knives professionally should not ever deliver a knife which can't cut properly.

Ken

[mike40]

Sharpening knives of any kind is certainly an interesting subject of which I know very little about. I can understand that there are many different types of edges for different types of knives. I sure would like to learn more about them and how they should be sharpened on the Tormek.

[Mike Fairleigh]

If I needed to re-true a knife edge, I would probably skip the electrics (unless it was tremendously out of shape) and use a bastard file with the knife chucked in a vise.  I'd think this would afford greater control and result in removing the least amount of steel necessary so as to preserve the life of the tool.

At the 21:30 mark in this video, you can see an example of using a file for re-shaping, but on an axe.  I've used this method and can tell you it will re-shape an edge in mere seconds.

https://www.youtube.com/watch?v=Xz3rs-eaN3E

Having said that, I've been looking very hard at how to justify a KMG belt grinder lately.

[Ken S]

Good thought, Mike.  In truth, I have a large drawer in my mechanic's chest dedicated to files.  The mill files get used a lot for all sorts of utility duty.  They have never let me down.

Ken

[Herman Trivilino]

I have a large drawer in my mechanic's chest dedicated to files.

That's the best tool to use to make sure the blade on your kitchen knife is everywhere convex.  Once that's done you can take it to the Tormek and get it sharp.

Having used the HK-50 now to sharpen dozens of knives I think it far better suited to the task than any method I've tried.

My final modification was to add a piece of adhesive backed felt to the surface.  The thinnest I could find was also the cheapest and available any place where they sell craft and hobby supplies.

[mike40]

KSMike, thanks much for that link. Very interesting and I learned a lot from it. At my age I'm not too interested in using axes, but the video answered a lot of questions about axes that I have long wondered about, but maybe not enough to actually search the net. I did split green logs earlier with axe and wedges, which I learned from a green woodworking book by Mike Abbot, and English woodworker. I was surprised at how easy it was to do, and I got a lot of good turning pieces that way.

[Mike Fairleigh]

You're welcome Mike, I'm glad you enjoyed it.  I never had the slightest interest in axes until someone else posted that video a couple of years ago.  I was fascinated by the history of the axe and the process of maintaining them.  I've used it as a guide to re-hang a double bit of my own, and have a new appreciation for the tool.  I even had a chance to put my double bit to use not long ago when I got my chain saw stuck while felling a mature pear tree in my yard.

[mike40]

I lived on my grandparents farm in Minnesota for a year during WWII when I was five years old Mike. All of the men in the family except my uncle who had health problems was in the military. My job was to split firewood for the wood stove in the kitchen. Thinking back, it must have been a pretty small axe considering that I could use it. The wood was Birch from our own woods, and it was probably only about 4" in diam. That stove did all the cooking and baking and also heated the whole house. I can't remember seeing the axe sharpened, but we had a big stone sharpening wheel not far from the front door, and the axe always worked well for me, so I guess my uncle kept it sharp, or at least sharp enough. I didn't mind that chore, as I thought it was fun and it made me feel useful.

[Herman Trivilino]

I'm no regular user of the ax, but I do know that a splitting ax doesn't need to be anywhere near as sharp as a felling ax.

I learned a lot watching that video and found it very interesting.

[Mike Fairleigh]

Mike, I suspect that during a Minnesota winter, they were glad to have anyone split as much wood as they were able!

[Stickan]

"Any light shining through between the edge and the cutting board indicates a hollow spot in the blade.  That part of the blade will not cut completely; things like green onions will not be cut through."

Use less time and pressure in the middle of the blade. Requires some practise but then the edge will have a perfect line.
I bought some expensive Japanese knives that came with an convex edge. They were sharp but my wife asked me to sharpen them after 5 days. And off course i did.
On those knives its impossible to feel any difference from convex to concave. I have some other good knives that came with a concave edge and all I do with all my knives is  sharpening once a year and honing 2-3 times a year.

[koolingit]

In my high school days, I used to work in a delicatessen.  They were kind of famous for their health salad and as a result, they made mountains of it. 

Once a week, a grinder would come with a set of sharp knives and collect the dull ones.  When he came, the cook would pounce on him and check all the chef's knives to make sure there were none with a concave edge.  If she found one, she's read him the riot act in German, pointing to the space between the middle of the blade and the cutting board insisting he take the knife back out and regrind it.  The grinder was Italian but he got the message loud and clear.  He would resharpen the offending knife and it only happened a few times in the time I worked there.

Very often, when I would be eating lunch in the kitchen, Tessie would be making health salad.  She was like a machine the way she could chop everything into quarter inch pieces and made it look effortless.  The action was half rocking and half forward motion and she could do it all day.

I always think of Tessie when sharpening a knife.

[Ken S]

Good thought, Stig.  Thanks; I will work on it.  I do think it would be valuable to keep a straight piece of wood near the Tormek to check the edge curve of kitchen knives.

Funny story, Koolingit!  It reminds me of growing up in New Jersey.  Good for Tessie!  We need more Tessies to keep the knife sharpeners honest (and knowledgeable).

Ken