Middle overgriding problem

[Ken S]

Wootz,

Knife sharpening would not be as much fun if it was easily and quickly learned. I hope you are like me and know more this year than last and hope to know more next year.

Keep learning!

Ken

[wootz]

If knife sharpening was easily learned, I would never logon to this forum and make the acquaintance of you, and a dozen of intelligent gentlemen here.

[Ken S]

On behalf of the forum, thank you for the compliment. Wootz. None of us has all the answers, however, working together we manage to nail down some of them. I am proud to be a member of this group and hope everyone feels that camaraderie.

Ken

[WolfY]

Dear friends,

This was a very important thread and the topic concern every knife sharpener on all systems. wheel, stones etc...

That's why good sharpener is a little of an artist. It's not "only" technical or mechanical to sharpen a knife.

My practice in order to spread the pressure on the knife is to hold fingers spread on the blade. With the other hand I hold the handle only on the horizontal plane and not around the handle for 2 reasons. 1. not to hit the honing wheel. 2. to be able to adjust the horizontal plane with more sense.
I normally start to sharpen checking the blade plan.

I seldom use pressure higher the the weight of my hands and then by hanging or forcing pressure. Only holding it so there will be low and firm pressure. But when I have a knife with uneven blade convex or concave I  add pressure and/ or time at this section. Mostly near the handle.
The reason it happens mostly near the handle is this;
1. When users need to hone the knife they use the steel and then starting to create the concave shape in the middle. That due to uneven force pressure when "steelin" the knife.
2. Blade steel lots of times thicker near the handle.
3. Blade edge on tip has, nearly always, narrower sharped edge. Meaning it will get dull faster and is used more during the work, compared to the part near the handle. Meaning it will "loose" more steel every time we sharpen compared to the rest of the blade. Therefore I start there with more cautiousness of the pressure I use.
Getting to the part near the handle I use little more pressure and/or time (as stated above).

Small tip: On kitchen knifes I take down the last (near the handle) 5mm | 1/4" and make it rounded/ dull for the safety of the user.

This are my 2 cents.

[Ken S]

WolfY,

What an interesting post; it makes me think.

We seem to have the idea that using the Tormek requires great pressure on the tool. I have been working more with the blackstone and have found that it works much better (and more quickly) with lighter. Even when using the regular SG grinding wheel, we usually do not require much force when sharpening knives, unless we wish to convert our chef's knives into paring knives.  Chisels and plane blades often have large nicks to be removed. Hopefully our kitchen knives are merely dull.

I first learned that my slicing knife had a hollow in the middle of the blade when my green onions were not being properly cut. Steve Bottorff shows a simple yet effective way to test for hollow in his Sharpening School DVD. I think a hollow test, which only requires a vew seconds, should become a routine part of knife sharpening.

I like your tip about rounding the last 5mm of the blade at the handle for safety. More and more I am learning that there is more involved in a quality knife sharpening than just making the edge sharp.

Ken

[WolfY]

Steve Bottorff shows a simple yet effective way to test for hollow in his Sharpening School DVD. I think a hollow test, which only requires a vew seconds, should become a routine part of knife sharpening.

Have not seen that VDO. Is it on Youtube or can you refer to, or explain this method?

I put the knife on plane surface with light towards me/ Then I can see the light/ arch under the blade. if there is any

[SharpenADullWitt]

I do wish Jeff would chime in, as I just watched his knife video again.  It appears he has his hand over the jig, but isn't using pressure on it.  I'd like to know if he had any issues with the center, as his lifting technique, does appear to put more pressure on the tip.

[Ken S]

The Sharpening School DVD I referred to was made by Steve Bottorff of this forum and available for sale on his website, www.sharpeningmadeeasy.com. Steve recently retired from teaching. His sharpening school focused on knives and scissors. It was two days of individual hands on instruction in his shop, with the option of another half day working as his apprentice at a local farmers' market. I have spent time with Steve. The DVD captures the essence of his school. I think it is outstanding and essential training for anyone interested in knife sharpening. Steve has generously posted some segments for the forum on you tube.

Steve has produced the kind of in depth knife sharpening video I have requested Tormek to produce.

Ken

[Ken S]

SADW,

I agree. However, unfortunately, Jeff Farris no longer has any association with Tormek, Sharptoolsusa, or this forum. His forum posts over the years are available for member study, something I do frequently.

Ken

[stevebot]

Thanks to Ken and Wootz for the mentions. I believe the technique Ken is referring to is for chef's knives and santokus, etc. that are meant to be used against a cutting board. These must have a continuous convex shape to the edge so that they maintain contact as they are rocked in use. The test is to rock the knife edge against the side of another knife. If the shape is proper it will rock silently. If there is a low (high?) spot there will be a decided click as the contact jumps from point to point.

[wootz]

To remind the context of the problem:
Knives where straight edge extends over 3" before it curves upwards, tend to concave in the middle when sharpened on a 2" rotary wheel.

The next picture shows how much grinding get different parts of the edge when pulled across the 2" stone from bolster to tip.
The 1st inch (the heel segment) gets the least grinding, the next 2 inches (red line) get approximately twice as much grinding as any other segment, and the 4th-5th inches get less grinding due to the sharpener lifting the knife handle as he follows the taper towards the tip.


Two weeks more of trial and error resulted in a technique delivering near perfectly straight edge.

See my post above for the right hands position.
Clamping the jig in the middle of the straight stretch (not in the middle of the knife) gives the best result.
Sharpening direction: unilateral from heel to tip.

Sharpening movement is 2-step: one short pass from the bolster for 1 inch, followed by 1 full pass from the bolster to the tip.

When doing the 1st inch pass, press on the heel only, and slightly slant the blade so that only 1 inch of the edge contacts the stone - water flow helps, as shown in the next picture.


Then start again from the bolster, press the edge flat on the stone, and do one full bolster-to-tip pass, with light pressure.


Flip the blade, and do the same on the other side. And so on alternating sides, till the burr forms.

With this technique, a continuous burr forms almost simultaneously all along the edge; the 4th-5th inch segment may be falling behind and where this happens I spend a little more time one it.
Note that to use this method, the stone corner must be smoothed out, just a little - I do it with a touch of the fine side of the stone grader for SG and SB stones, and with Nagura for SJ.

perished for a good cause in experimentation...

[Jan]

Wootz, thanks for the visually well documented post concerning the middle overgrinding problem. It is so clearly written that everybody will remember it for a long time. 

I believe that also these training knives can be resurrected to a new life with a straight edge. I would definitely give them another chance. Live and let live. 

Jan