Topic: Tormek is good, but can't thinning. So...

[Sharpco]

I believe Tormek is a great sharpener.

But even though I think and think about it, there seems to be a definite limit to making the blade thin with Tormek.

A seriously worn knife must be made thin, and some people require thinning it every time I sharpen.

How do you solve this problem?

I think there is only way to use Belt sander for quick work.

[cbwx34]

You can do the “thinning behind the edge” with the Tormek, but the entire blade thinning, I’m with you on the belt sander, for a quick decent job.

[Ken S]

I don't think most of us, myself included, have thinned a knife. I have only sharpened my own knives, perhaps twenty including the kitchen knives, pocket knives and practice knives. The Tormek handbook does not discuss thinning knives. I would guess it would be done by setting a more acute angle with the knife jigs. Yes? Has anyone tried it with a Tormek?

I am not arguing that it would work efficiently; I am merely stating that I have not tried it. Does it not work at all or just not work "quick"? Obviously, for a busy professional sharpener with a hundred knives to sharpen on a Saturday morning, even five or ten minutes would not be acceptable. For a less hectic sharpener, either a drop off service or a home sharpener, an occasional thinning job, even if it required half an hour, might be acceptable.

I do not doubt that a belt grinder could do the job quickly. In fact, I would probably turn first to my belt grinder. I have modified my belt grinder to have a variable speed motor and a high torque drive. It makes a useful complement to my Tormek. However, "quick" comes at a price. With all of the modifications, the cost of my belt grinder is in the range of another Tormek. Unless someone did a lot of thinning work, the extra hours involved in esrning the money to pay for the belt grinder would slow "quick" considerably.

Could the thinning be done on a Tormek using a CBN wheel? I have used CBN wheels on a Tormek both wet and dry. Wet is cool and dustless. Dry is warm, much more controllable heatwise than a belt grinder with about equal dust. I would expect the grinding time to be comparable. Costwise, a CBN wheel, especially the new Spartan series, would be considerably less than a quality belt grinder, and still allow the control of the Tormek.

I would agree that a belt sander may be a very good tool for knife thinning. I would question it being the only good way.

Ken

[cbwx34]

I don't think most of us, myself included, have thinned a knife. I have only sharpened my own knives, perhaps twenty including the kitchen knives, pocket knives and practice knives. The Tormek handbook does not discuss thinning knives. I would guess it would be done by setting a more acute angle with the knife jigs. Yes? Has anyone tried it with a Tormek?

I am not arguing that it would work efficiently; I am merely stating that I have not tried it. Does it not work at all or just not work "quick"? Obviously, for a busy professional sharpener with a hundred knives to sharpen on a Saturday morning, even five or ten minutes would not be acceptable. For a less hectic sharpener, either a drop off service or a home sharpener, an occasional thinning job, even if it required half an hour, might be acceptable.

I do not doubt that a belt grinder could do the job quickly. In fact, I would probably turn first to my belt grinder. I have modified my belt grinder to have a variable speed motor and a high torque drive. It makes a useful complement to my Tormek. However, "quick" comes at a price. With all of the modifications, the cost of my belt grinder is in the range of another Tormek. Unless someone did a lot of thinning work, the extra hours involved in esrning the money to pay for the belt grinder would slow "quick" considerably.

Could the thinning be done on a Tormek using a CBN wheel? I have used CBN wheels on a Tormek both wet and dry. Wet is cool and dustless. Dry is warm, much more controllable heatwise than a belt grinder with about equal dust. I would expect the grinding time to be comparable. Costwise, a CBN wheel, especially the new Spartan series, would be considerably less than a quality belt grinder, and still allow the control of the Tormek.

I would agree that a belt sander may be a very good tool for knife thinning. I would question it being the only good way.

Ken

You should try it.   

Some sharpeners consider thinning part of the sharpening process... Murray Carter probably being the biggest advocate of this.  He thins every time he sharpens a knife, to maintain the "proper geometry".  Thinning seems to be more prevalent on Japanese style knives than Western style... still, it's becoming more common especially on a lot of EDC (pocket) and hunting/camping knives that can come pretty thick.  (And Murray Carter is Japanese trained... so probably another clue).  He calls it sharpening the "secondary edge".  Here's a video where he talks about it on an EDC...

www.youtube.com/watch?v=iJdtCLIGQm8

You can't really thin a knife in a jig... since it typically involves thinning the entire side... a jig won't allow that (with the exception of the Small Knife Jig).  Also the curve of the wheel makes it difficult to do... it'll leave grind marks or lines (not sure how to really describe it), since the curve of the wheel won't contact the entire side of the blade at the same time.  (So, type of wheel i.e. CBN wouldn't matter either... a better wheel is actually the 1K King waterstone, you can 'blend' the grind marks a bit better).  So, even if you could put it in a jig, it would be hard to get an even grind on a wide surface, with a curved wheel.  You can, as I mentioned earlier "thin behind the edge", depending on the knife, which will improve cutting performance.

That being said... I've done it freehand on the Tormek... just to see if I could get a decent result, for example...



... this was done on the stock Tormek wheel.  I've kinda figured out a technique that works pretty well, but it's a bit slow, and not sure if it's a technique I would do on a 'customer' knife...  you can see a few of the anomalies I mentioned.  A belt sander is not only quicker but produces a better result.  Second choice would be a flat stone, for the reasons mentioned above.

[Ken S]

Good post, CB. I will file your thoughts in my memory bank for the day when I actually thin a knife.

By an odd coincidence, I happened to watch a couple Murray Carter videos. I was impressed. In one, he used a cinder block. I thought that would be heavy duty artillery for when the SG doesn't seem coarse enough.

Ken

[brettgrant99]

Good post, CB. I will file your thoughts in my memory bank for the day when I actually thin a knife.

By an odd coincidence, I happened to watch a couple Murray Carter videos. I was impressed. In one, he used a cinder block. I thought that would be heavy duty artillery for when the SG doesn't seem coarse enough.

Ken

I think that you supposed to use the cinder block as a stone grader to get the SG grit really coarse.  That way, you can still use your Tormek.

[Sharpco]

Ken.

I tried thinning behind the edge with the Tormek. My choice is abt. 7 degrees. There are no 7 degrees on the scale of the Angle master, but the rough setting is possible. The result was not bad. Thinning behind the edge is possible with Tormek.

However, the thinned surface does not appear broader when using a whetstone or belt sander. People don't like it.

Another problem is that a small knife cannot be set at a sufficiently acute angle.

[cbwx34]

...
Another problem is that a small knife cannot be set at a sufficiently acute angle.

How small (or what type of knife)?  The "Small Knife Holder" does a good job... (even on EDC type knives).

Good post, CB. I will file your thoughts in my memory bank for the day when I actually thin a knife.

I should have mentioned, in addition to thinning, it can also be used as a good way to "clean up" the side of a knife...  for example, getting rid of some light rust, or maybe scratches on the side of the blade from another sharpener. 

[Stickan]

Hi,
I wonder if we are discussing a minor "problem" here.
Thinning a knife is not something most sharpening centers are doing in my experience and I have meet a lot of them during my years at Tormek.
I can't remember someone who have mention this before. Thinning a blade every time you sharpen will change the way the knife was designed to work.
The comparison I can think of is a regular Mora carving knife, then you sharpen the hole edge on the Tormek without any difficulties. But again, that edge is about 10-12 mm on a new knife.
I'll talk to some of my contacts in the Knife manufacturing industry how they think about it as I can only reefer to my own experience.

Best,
Stig

[cbwx34]

Hi,
I wonder if we are discussing a minor "problem" here.
Thinning a knife is not something most sharpening centers are doing in my experience and I have meet a lot of them during my years at Tormek.
I can't remember someone who have mention this before. Thinning a blade every time you sharpen will change the way the knife was designed to work.
The comparison I can think of is a regular Mora carving knife, then you sharpen the hole edge on the Tormek without any difficulties. But again, that edge is about 10-12 mm on a new knife.
I'll talk to some of my contacts in the Knife manufacturing industry how they think about it as I can only reefer to my own experience.

Best,
Stig

Thinning a blade will actually maintain (or improve) the performance of a knife... not "change the way the knife was designed to work".  I'll refer you back to Murray Carter's video, although he's not the only one. I'm sure you know that on many knives, as it is sharpened, it constantly moves into thicker metal, reducing its performance.  The Tormek manual sort of addresses this in the "Shaping and Sharpening" section, but doesn't really address blade thickness, only returning the edge to its original angle.  Would you agree that a 40 deg. edge on a 2mm thin blade would perform (cut) better than one that is twice as thick?  And many knives come "thicker than needed"...  I would bet in part a manufacturing decision, since a thinner blade can be more prone to damage, and are made in part, on how the knife will be (ab)used.

I don't think it's a "problem", but it is an aspect of sharpening that comes up.  The reality is, those who do any thinning, aren't likely to have a Tormek in their arsenal... they will use the same equipment to sharpen that they use to thin.  That may be the main reason this has never been addressed here.  The same will probably hold true of the contacts you're used to dealing with... if they're using a Tormek... then like you, it may be something they wouldn't deal with.  Also, manufacturers don't really have to deal with it, since resharpening isn't a normal task, and as I indicated earlier, their goals are a bit different. 

You are correct that most sharpeners never deal with this... they just reshape and sharpen the edge... what the Tormek is good at.  Style/type of knife also matters. We are talking about a niche group, however it is a group that is growing.  There are now businesses that deal specifically with this... probably one of the better ones is Razor Edge Knives... whose main business is doing "regrinds"... which is essentially blade thinning... you can see the results on his website... and here's a thread that talks about it... Insane performance boost in cutting ability.

The Mora knife you referenced is actually a good example of thinning... since you're sharpening the whole edge, you're essentially thinning the blade every time it's sharpened. (Any true Scandi grind is essentially thinned every time it's sharpened).  Wider knives, unfortunately, don't thin well on the Tormek size wheels.

[Ken S]

I have been puzzled with this topic. I watched the video where Murray Carter demonstrates thinning a knife blade using a very large wet grinding wheel. The wheel looked to be three or four times the size of a Tormek wheel. The knife involved was a Japanese style knife Murray had forged. He used the traditional method of forging hard steel and softer steel or iron together. He stated that he forges these knives overly thick to compensate for heat treating problems, and then thins them.

I have never seen, used, or sharpened a knife of this quality or price. I doubt most of us have. I cannot imagine Murray Carter condoning thinning one of his knives with a high speed belt grinder (or with a wheel the diameter of a Tormek).

In your last post, you compare a forty degree bevel with knife thicknesses of two and four millimeters. My Henckel chef's knife is tapered. However, I would retire the knife long before it approached double thickness. For what I would consider the useful life of the knife, I don't see any need to thin the blade. My grocery store knives appear to be flat. They should never need to be thinned.

I sharpen my kitchen knives with the standard fifteen degree (thirty degree total) bevel. I have not noticed a problem.

I admit that I have never sharpened more exotic knives, either straight or folding. My everyday pocket knife is a humble Swiss Army Tinker.

I can imagine a belt grinder like mine (modified for variable speed and higher torque) doing an acceptable job of thinning more utilitarian knives. You might find a good market niche with this.

Ken

[Sharpco]

I think all kitchen knives need thinning. Because some people use it for a very long time until the knife completely loses its original shape, and some people use a knife that has thickened the edge from the beginning by modifying the knife.

And you will know the sharpener called Tru Hone. It's hard to say that it's better than Tormek, but the price is higher, and surprisingly there is a Thinning function.

https://www.youtube.com/watch?v=N8tO9AuhFBk


P.S. I do not think thinning is necessary for Scandi knives.

[Ken S]

Looking at my kitchen knives, I do not see where they would need thinning. My Henckels are taper ground, however, the taper is gradual. If the knife was used long after it needed to be sharpened, I would think that removing no more than 1/16” or 1.5 mm would restore the edge. I don't think the thickness of the blade would increase much in that 1/16”. With my more modern, thinner, bolsterless knives, the sides appear to be flat. With any knife, I would be surprised to see it in active original service as it approached half width.

For anyone working full or part time as a sharpener, part of the service should be educating one's customers about knife care, including more regular sharpening. This is no different than an honest mechanic recommending regular oil changes or tire rotation.

I watched the tru hone video you linked. It reminds me of the F Dick machines. I am sure either will produce sharp edges. After watching the video where Murray Carter thins a blade on a very large (perhaps 1 meter diameter) wet grinding wheel, I question how effectively the very small wheels (perhaps 4” or 100mm) on the Try Hone would work in thinning mode.

Ken

[Sharpco]

Ken.

I think the Tru Horn can only thin behind the edge. Of course, Tormek is also available.

[Herman Trivilino]

I would guess it would be done by setting a more acute angle with the knife jigs. Yes?

The bevel angle would be too acute for a Tormek jig. Less than 5° on my butcher knife, and I have a hard time with a 10° bevel because it's too acute. Razor blades have a bevel angle of about 10° if I'm not mistaken.

I soon discovered when I bought my Tormek back in 2002 that it appeared impossible to measure bevel angles with the AngleMaster on knives with tapered edges, so I stopped buying them. All of my kitchen knives that I use regularly have parallel, or nearly parallel, sides. I do have pocket knives with tapered edges and have since learned how to use the AngleMaster to measure their bevel angles, but doing it is a pain.

Blades with parallel sides never need to be thinned. The Houston area sharpening service that I use for carbide-tipped circular saw blades and hand saws has a machine dedicated to thinning knives and the owner is of the opinion that such a machine is necessary for the task. A well-experienced knife sharpener could no doubt do it free hand using a Tormek. I can't.