Topic: How to sharpen single-bevel Japanese knives on Tormek

[wootz]

When sharpening single-bevel Japanese knives, I used to polish the back flat side on bench stones, then grind the beveled side on Tormek.
But yesterday we got a dozen of single-bevel Japanese knives to do, and I told myself there should be a better way.
And yes, it is. Our new procedure follows.
We are getting 70-90 BESS on the sharpness tester.
Using 2 Tormek machines, one with the Japanese SJ wheel and the FVB, and another with #200 (or #400) and #1000 grinding wheels, it takes 10-15 min per knife.

1. Measure the existing edge angle with a laser protractor, if ordered to reproduce. Our default for quality high-carbon Japanese knives is 16 degrees; lower-end knives we sharpen at 20 degrees.



2. Clamp in a knife jig.
Using our Frontal Vertical Base at the front of the Tormek, position the knife so that the backside edge rests on the wheel with the knife jig parallel to the top of your Tormek.
Polish the flat back on the Japanese wheel SJ-250 horizontally - initially do just 2 passes.
You will get a narrow polished strip all along the edge; don't bother if it is not ideally uniform at this step.




3. Set the grinding angle using our computer software "Grinding Angle Setter".



4. Grind the bevel side into the edge on a coarse wheel, e.g. SG-250 grit 220, or diamond wheel DC-250, or a CBN wheel.



5. Using our Frontal Vertical Base at the front of the Tormek, polish the flat back on the Japanese wheel SJ-250 horizontally; usually 1 pass is OK.



6. With the help of our computer software "Grinding Angle Setter" calculate the Universal Support height for the next grinding wheel.
Grind the bevel side into the edge on a fine wheel, e.g. a 10” Japanese wheel JIS 800, or a diamond or CBN wheel #1000-1200.
Typically it takes 2-4 passes.



7. With the help of our software for the Frontal Vertical Base calculate the Universal Support height for honing on the leather wheel.



8. Hone the beveled side at the edge angle on the Tormek leather wheel with the Tormek honing paste; typically 2-4 passes.



9. Using the Frontal Vertical Base, deburr the flat back on the Japanese wheel SJ-250 by 1 horizontal pass.



10. Finish on a hanging strop by 6-10 passes alternating sides.



11. Test sharpness.

Works like a charm for quality high-carbon knives.
However, with softer knives like Kamikoto etc, requires an extra step to remove the wire edge. We do it by honing on a rock-hard felt wheel on Tormek with 1-micron diamonds @ +3 degree higher than the edge angle, controlled by our FVB, alternating with the flat back of the knife on the same felt freehand at an angle just clearing the knife jig, x 3 passes.

[Antz]

Thanks for sharing that info Wootz. So you polish just the flat back close to the edge? I’m trying to picture it in my head.  Perhaps possibly a YouTube video will be in the near future? 

Thanks,
Antz

[wootz]

Yes. I position the knife jig on the FVB so that the backside edge sits flat on the SJ wheel.
When developing the protocol, I even checked with the Angle Cube the knife jig is at 0 degrees, i.e. parallel to the top of the Tormek.
Where the single-bevel knife has Urasuki, the concave backside, we get only 1 mm polished near the edge.

[Josu V]

Thank you very much. I'll try it with the next single bevel knife.
Knowing the price of a good Japanese bench stone  with 15,000 or 30,000 grits, this procedure is a valuable information.

One question:
I have not a plain leather hanging strop to finish the flat side, but I have this one:
One side with a layer of leather, and the other side whith a layer of leather with chrome oxide.
Do you think it is valid?

Regards

[wootz]

Josu, the hanging strop "gives" as we drag the blade, and thanks to that stropping goes at a higher angle removing the wire edge, if any.
The firm strop cannot do it.

I borrowed this technique from the straight razor sharpening - they hone the razors on firm strops with Chromium Oxide or other fine compound, and finish by 10-14 strokes on a hanging leather or linen strop. Straight razor steel can be likened to mainstream knives.

On a smooth horse or cow hanging strop, the sharpness tester shows improvement in the edge of mainstream knives after 4 strokes; we normally do 6 - 10 stropping strokes alternating sides. Wear-resistant "premium" knife steels do not show such improvement on the horse/cow hanging strop, but do show on the Kangaroo tail strop thanks to its texture.

You know that we hone on paper wheels, finishing on the 0.25-micron diamonds + Cr2O3 wheel. But some knives, after the finishing paper wheel,  show worsened score on the sharpness tester even though they show improved keenness in conventional tests like hanging hair tests. This happens because with some knife steels the intensive honing on the paper wheel over-thins the edge near the apex. These knives we finish on the hanging strop instead as it gives a stronger apex.

In your Spain the bull leather from Corrida can make a good hanging strop
On the photo is a quick hanging strop that takes no time to make and works for knives:

[Antz]

Wootz, do you ever use compound on your strops? If so what type of compound is best for what type of strop (cow/horse/kangaroo). Also do you use the smooth side or the rough side.

Thanks,
Antz

[wootz]

We hardly ever use firm strops in our knife sharpening. The Tormek leather wheel, paper wheels and hard felt wheels cover all honing and stropping we may need. But we do use hanging strops for their help with the wire edge removal, plain w/o honing compounds. We use it plain because when we take the knife to the hanging strop, it has already been honed on the wheels. Someone who does not hone on the wheels, may be using the hanging strop with honing compounds.

[Antz]

Thank you for sharing Wootz. I’ve only done a couple of single bevel Japanese knives and my method was pretty similar to yours except polishing of the flat back was done on paper wheel freehand. I have no idea what sharpness I was getting because I don’t have a Bess tester but I know I could push cut notebook paper. When I get an sJ wheel I’ll definitely try your method. Thanks for updating with pictures. Great post as usual Wootz!

Thanks,
Antz

[Josu V]

Thank you very much Wootz.
I have it clear (now).

The next steep is to get one hanging strop and work with it.

Good post!!!

[john.jcb]

I have a Japanese single bevel knife that I got a few years ago for almost nothing at a store that sold closeout items from large department stores. It is quite sharp out of the box. I have never used it; being left handed the bevel is on the wrong side. I think I will give it to my daughter to try. Once it dulls I will use this method to sharpen it and expand my skills.

[van]

Thanks Wootz for sharing, very interesting protocol

[wootz]

The procedure is now supplemented with a video on our YouTube https://youtu.be/dhpajIaBW0c
We sharpen this way all single-bevel knives, not only the Japanese.

There was a question why the hanging strop for wire edge removal.
We use the hanging strop for single-bevel knives because asymmetry of their edge makes the wire edge removal somewhat tricky on the wheel. Also, stropping saves time when you do many knives and cleans the apex of the wire edge good enough.
But of course, a felt or Tormek leather wheel with 1-micron diamond paste removes the wire edge better than a plain leather hanging strop, even of the Kangaroo tail.

[Sigs]

Such a great series of posts. Thank you all for sharing and asking the pertinent questions. Always learn a lot from these posts.