Knife tip grinding - To Pivot or Not To Pivot

[Jan]

Cbwx, in my thinking grinding the edge of a blade is a trade-off between pivoting and handle lifting. In some situations raising the handle is enough in other situations pure pivoting is sufficient. In every day practice, I think, it is a combination of both.

Handbook picture shows pivoted blade and the text mentions rising the knife handle near the tip. 

Jan

[Herman Trivilino]

To avoid pitching, you do not yaw, you roll.

See this video of Jeff Farris using the SVM-45 to sharpen a knife:

www.youtube.com/watch?v=fYURcwkKGPs

If the link doesn't work go to YouTube and search for "Jeff Farris Tormek knife".

He discusses this issue starting at about 5:45.

Now, I have found that if there's large curvature at the knife tip, like on a butcher knife, this technique doesn't work as well. You have to pay attention to where on the knife you attach the jig. The closer you get to the tip the more blunt the bevel angle. But as I said in my previous post I get around all these issues by using a platform jig. To me it makes all three of the Tormek knife jigs obsolete, and it's sure a heck of a lot cheaper, And it's faster, too. Faster, better, and cheaper; you get all three!
 

[Ken S]

Herman,

You and I shar a common frustration: I honestly believe the kenjig and its variations are the most efficient, accurate and repeatable method of setting up the Tormek knife jigs (other jigs, too). I have long believed, just as fervently, that your small platform jig is one of the most useful and versatile jigs for the Tormek. Neither of us has made the slightest effort to conceal the secret sauce of these ideas, yet, neither idea has been generally accepted. (I might think that some of the sharpening community still believe the earth is flat, but that would not be polite to post)

Ken

ps. It has always been a mystery to me that, if following Jeff Farris' technique of lifting the knife rather than pivoting, why does the adjustable stop on the knife kig have a large radius? I hope one of the first videos produced in the new Tormek studio will be an in depth knife video addressing this issue and several other knife sharpening issues.

[cbwx34]

I do concede that the jigs radius may have been so that the knife could be pivoted (yaw) (although I feel in use it's more of an afterthought).

Setting that aside though, I think lifting (roll) can achieve the same result... and, to me anyway, fits the design/setup of the knife jig.  (The Jeff Farris video is what I was referring to earlier).  The change in angle by changing the point of contact on the stone, can be offset by the "side" angle you create by jig placement.

Herman, I have not overlooked your setup.... I think it's a good one, and will probably be my next venture.  I do have a couple of questions... do you ever have an issue scratching/scuffing the side of the knife?  With other platform based sharpeners, that's often the case, but it's also because the 'swarf' can get on the platform, which may not be an issue with the Tormek (since it's for the most part washed away).  Also, when you set the angle, do you compensate for the angle of the blade itself? (Not the bevel, but the actual angle of the blade grind).

All in all, I think Wootz was onto something in his original post.. that pivoting the knife introduces more factors than merely maintaining the same point of contact on the stone... when using the jigs.

[Ken S]

Here is a link to a video by Ken Schwartz. Ken is the guru who has concocted many of our best modern honing compounds. This video covers tipping a knife when the knife is not held level.

https://m.youtube.com/watch?v=JFhUXgYS0Os

I think the idea presented is very sound. I should note that essentially the same idea is presented by Steve Bottorff in his Sharpening Made Easy book.

I believe there are gains to be made in technique for sharpening knives with the Tormek, both with jigs and without.

Ken

[Jan]

It has always been a mystery to me that, if following Jeff Farris' technique of lifting the knife rather than pivoting, why does the adjustable stop on the knife kig have a large radius? I hope one of the first videos produced in the new Tormek studio will be an in depth knife video addressing this issue and several other knife sharpening issues.

I do concede that the jigs radius may have been so that the knife could be pivoted (yaw) (although I feel in use it's more of an afterthought).

Wootz has been striving to keep the width of the bevel face constant. He achieved this goal by lifting the handle without pivoting at the expense of maintaining constant edge angle. He admits that the edge angle set at the heel to 30° has increased to 34-42° near the tip! 

I am convinced that using suitable trade-of between handle lifting and blade pivoting would not increase the edge angle so much.

The water flow over the edge is for me another reason to pivot the blade. When the blade is pivoted so that the outer normal of the blade in the belly area is perpendicular to the stone shaft, then the water flows symmetrically over the edge. This is good to achieve. My hands do it unconsciously.

Jan

[cbwx34]

Wootz has been striving to keep the width of the bevel face constant. He achieved this goal by lifting the handle without pivoting at the expense of maintaining constant edge angle. He admits that the edge angle set at the heel to 30° has increased to 34-42° near the tip! 

I am convinced that using suitable trade-of between handle lifting and blade pivoting would not increase the edge angle so much.

The water flow over the edge is for me another reason to pivot the blade. When the blade is pivoted so that the outer normal of the blade in the belly area is perpendicular to the stone shaft, then the water flows symmetrically over the edge. This is good to achieve. My hands do it unconsciously.

Jan

How so?.... If bevel width is the goal... I'm not sure either method would result in a better angle result... seems to me it would have to be the constant to keep the bevel width the same.  (It's the same result you see on production knives... nice looking bevel, but steep angle, and most of those are freehand sharpened).

Although I primarily sharpen with the wheel turning away... I do use the water as an indicator of where the wheel & blade are contacting... I can do it with either method.  Like you indicated, it's not the primary way though... you can usually feel it.  But I can see the water 'travel' along the edge, especially as I lift the handle to the tip... good indicator of when it's reached.

[Herman Trivilino]

I do have a couple of questions... do you ever have an issue scratching/scuffing the side of the knife?  With other platform based sharpeners, that's often the case, but it's also because the 'swarf' can get on the platform, which may not be an issue with the Tormek (since it's for the most part washed away).

Yes, although there was a forum member who claimed he didn't get scratches. I believe he must have used a much lighter touch, perhaps touching the platform but applying no force to, using it only as a guide to keep the angle constant. I found that the cheapest adhesive-backed felt, found in those fabric stores that sell sewing supplies, applied to the top of the platform works great.

Also, when you set the angle, do you compensate for the angle of the blade itself? (Not the bevel, but the actual angle of the blade grind).

Yes. When the sides of the blade are not parallel, and you want to measure the angle using the WM-200 or the like, you do need to account for this. There is a post somewhere where I describe this. After setting the platform at the angle I want, I lay the knife blade on top of the platform again and measure the angle of the upper surface of the blade's side. For example, say the platform is set at 20° and the upper surface is at 24°. Half the difference is 2°, so if I want the bevel angle to be 20° I reduce the platform angle by 2°, setting it at 18°. Usually, though, I don't care about a 2° error.

[Jan]

How so?.... If bevel width is the goal... I'm not sure either method would result in a better angle result... seems to me it would have to be the constant to keep the bevel width the same.  (It's the same result you see on production knives... nice looking bevel, but steep angle, and most of those are freehand sharpened).

Yes, the bevel width consistency is important, but the change of the edge angle from 30° at the heel to 42° at the tip is too large for me.

My point was, that the handle lifting accompanied by small pivoting may result in very small bevel widening (e.g. 0.25 mm = 0.01") while reducing the edge angle increase towards the tip substantially.

Jan

[cbwx34]

Herman, thanks for the additional info.

Jan, still don't see it, but I'll ponder your posts.

Ken, that video you linked to actually claims you can't just lift the handle without also pivoting the knife (around 3:42)... not a position I support.

Thanks to all.

[Kavik]

On topic: I sharpened my first knife on the tormek this past week. Just a cheap paring knife with a thick blade that I use as a utility knife for small tasks, so i didn't mind grinding it different ways and multiple times as practice.
The way that ended up working the best for me (to get an even bevel width and look good) was both pivoting and lifting, but the key thing that made this work was the diagram found in the manual describing how far from the tip to place the jig (as seen in the attachment on this post from another thread)
Only in that position did the lift and pivot feel like one smooth motion and give good results from a visual standpoint.


A little less on topic, my 2 cents on the "issue" behind the original topic:
(grab a coffee and get comfy, or feel free to skip to the Cliffnotes at the bottom)
I've always been confused as to why anyone is concerned over even bevel width in the first place. 
Does it look nicer? Sure. I guess this makes it good for your collectables/drawer queens/wall hangers.
Does it make for an optimal cutting tool? In some cases it may (either by pure luck, or by very careful design of a skilled knife maker), but I think in the majority of cases it won't.

That pig sticker, for example: the OP said the primary cutting surface measures around 30°, while the tip is up to 42°.  In my opinion that could actually work too this particular knife's advantage. A double edged blade that is intended to stab/thrust/puncture should have a sturdier tip. The last thing you want is for the tip to be thinner, wedge in mid - penetration and snap off.
As long as the edges are good and sharp i don't think the bevel angle at the tip is all that important in that case. The rest of the knife that may be used for slicing tasks can focus more on ideal angles.

Compared to that "sashimi" knife (yanagiba), the idea of keeping an even bevel width wouldn't even cross my mind for a second. No way of knowing just from the picture if that was an even bevel angle all the way to the tip in this particular instance, but i've seen knives like this with even bevel angles that varied more than that in bevel widths. (now, on a single/chisel grind knife like that... whether that difference should be dealt with at the edge on a secondary bevel, as seen above, or on the shinogi during thinning.... Or even if a secondary bevel should exist in the first place.... Those are much more in depth discussions of their own)
In this case i feel that keeping a proper bevel angle is much more important, as it's intended for very delicate work and should perform equally from heel to tip.

Likewise, for a chef's knife/gyuto/kiritsuke/santoku, and in many cases paring/petty knives for general purpose kitchen use; I would focus on the bevel angle rather than bevel width on these as well.
In general I would be looking for an even bevel angle throughout. If not kept even, then I would be leaning towards more acute at the tips for more flexibility in delicate work. With most cutting it's rare for the actual tip to be hitting the cutting board anyway, so a more delicate tip shouldn't be an issue. That said, the user needs to be aware and keep it in mind during use.

On the opposite end of the spectrum: a Deba, which is designed for breaking down fish, actually is thicker at the heel by design. This is intentional to be sharpened at a more obtuse angle as you approach the heel.  This gives you a heel that can chop bone, while the rest of the blade is better at slicing.


Now, at the risk of making this longer than anyone wants to read (if we're not there already  ), everything above also assumes we're only dealing with perfectly straight knives that, if wider at heel or tip, have a consistent taper along the whole length.
Know where we see that most often? In mid-range production knives, the kind that are stamped then machine ground. And who usually owns those knives? People who don't care how perfect they look, who aren't likely to spend much on getting them sharpened, and probably own a cheap pull through sharpener, and maybe a honing rod.
But get into higher end knives, that are forged rather than stamped, quenched for heat treatment after shaping rather than heat treated then milled to spec in sheets, ground to final profile by hand.. Then you start seeing inconsistent thicknesses,  spines that aren't dead straight, and over/under-grinding issues respectively.
And who most often owns these knives? People who care about function over form, who are willing to shell out this kind of money for a sharpening system, or who will spend $$$ on professional sharpening.....and these are also the kinds of people who will be picky about your results and the kinds of knives that will be expensive to replace if you screw them up...

That's not to say you won't see any or all of those issues in production knives, or that equal care shouldn't be put into sharpening the "cheapies". 
I grabbed a handful of low-mid range knives and took some measurements the other day, measuring 1mm behind the blade (2mm on the thick knives where the bevel was longer than 1mm) to do some math. Even the production models showed varying thickness along the edge.  Funny enough, the one with the most consistent thickness was the only handmade blade in the bunch.
It I were to focus on maintaining an even bevel width:
-A Kershaw Blur ranged from 0.58-0.51mm wide. If the bevel angle were set to 30° at the widest point then the narrowest point would taper down to 26.3°. If the angle were set at the narrowest point then the widest part of the blade would hit 34.23°. 
Not too terrible, but I'd rather keep the same angle and let the bevel width change by 0.14mm
-A Cold Steel SRK ranged from 1.37-1.17mm wide. If the bevel angle were set to 40° at the widest point then the narrowest point would taper down to 33.97°. If the angle were set at the narrowest point then the widest part of the blade would hit 47.22°.
Here a consistent angle could have been held with the bevel width tapering from 1.71-2.0mm.
-An old EdgeMark hunter ranged from 0.62-0.37mm wide. If the bevel angle were set to 30° at the widest point then the narrowest point would taper down to 17.77°. If the angle were set at the narrowest point then the widest part of the blade would hit 51.4°. 
Pretty nasty range on this one. Keeping a consistent angle here would still only mean a .54-.91mm bevel width, not a big deal IMO
-A CRKT SnapLock ranged from 1.74-1.36mm wide. If the bevel angle were set to 30° at the widest point then the narrowest point would taper down to 23.0°. If the angle were set at the narrowest point then the widest part of the blade would hit 39.77°. 
This one was perhaps the most surprising, as the cutting area is only like an inch and a half long, and the edge itself is practically a straight line. And with this one, to keep a consistent angle, the bevel width would vary from 1.36-1.74mm. Not insignificant over that short length, but not terrible.
There were others, both better and worse, but that should give enough of an idea.



To summarize, my point is that there is no one right answer for how we can treat every type of knife.  If the ideal end result can't be expected to be consistent between different styles of knives (not to mention the manufacturing or conditional inconsistencies), then there's no way a single jig setup could ever be achieved. 

Either way, in my personal opinion they should all be sharpened for performance, not for looks.

[cbwx34]

Thanks for the info. (I survived the whole thing).   Couple of thoughts/questions...

You said lifting + pivoting gave the best result... what differences did you see in that vs the other ways?  You are right, regardless of method... the placement of the knife in the jig is key.

As for bevel width... I agree with what you said, about looks vs. performance, but in a commercial sharpening setup... looks probably take precedent in most cases.  You're not going to convince most people (or even have the time to if you do a lot of knives) that the knife "looks funny, but will work better... honest".   So, to some degree (pun intended), things need to look good.

I'll have to digest the numbers.  Good documentation though... thanks.

[Kavik]

Lol congrats. Even I had a hard time getting all the way through when proof reading back through it (to be honest, it was written over a few sessions)

If memory serves (forgive me, it was just the one session, with just one knife, and it was a few days ago), but i believe it was that just lifting the handle resulted in a more obtuse angle at the tip, as it rode down the stone. And just pivoting sideways would end up with a wide bevel earlier on, as I'd have to grind through the area in front of the tip before the tip would make contact


Yeah, i can see where a clean edge and an even bevel would be preferred on a fast paced setting for random customers, that's why i stressed it being my personal opinion.

I've had knives that could pass every sharpness test thrown at them,  but couldn't cut a raw carrot without snapping it. But thin the blade profile down a bit on the whetstones, really ugly up the whole surface in the process, then resharpen and it cuts like a whole new knife 
Others that could cut fine, but always "steered" into whatever you were cutting...change the bevel angle just a hair on one side of the blade and voila, even slices every time.
It's funny how much of a difference just a fraction of a mm can make in the way a knife performs, whether the adjustment is in the face or in the bevel angle (especially so on the single bevel knives)

[wootz]

Hello Ken, Jan, Herman, Rich and the new sharp guys.
Apologies for being offline for so long, was too busy establishing my knife grinding business.

Appreciate reviving my topic I wrote when was new to Tormek.

The main conclusion drawn from that little study is the contrary effect of the blade taper towards the tip and upward curvature:
Because of blade thinning towards the tip grinding angle drops and contact with the stone extends and bevel should widen. However, the belly upward curvature brings the tip towards the support, increasing the grinding angle and compensating for the taper, and therefore the bevel height doesn't noticeably change.
Thanks to that for knives with a normal sweeping curve, no need to pivot/yaw.

Both the Tormek manual section on knife grinding and Jeff Farris video are (...how to say) ...if you think they are right you are still about a dozen fucked up edges far from the right technique.

[Kavik]

Hello Wootz, glad to have you back in the conversation

I don't know if you read my whole big long book there, but the main point/question of it was: which is the "f'ed up" edge? The one with the uneven bevel width, or the one with the uneven bevel angle?
Angle may not be so critical on a pocket/utilityknife, but in kitchen knives it can make a big differing in the way it cuts, that angle is far more important on some knives than the width is.

Particularly that single bevel yanagiba again.  I know it's been ages since you sharpened that knife, but i would've loved to have known what the final bevel angles were after you "fixed" it by making the bevel width even.
(also curious if you did any work on the shinogi or if you only ground the cutting edge? Ideally you would want that to move up the side equally with the sharpening, to keep the geometry correct.....something that I doubt can be done on the tormek, I'm afraid)
My guess is that if the main body of the blade allowed for nice, even cuts....I bet it steers into the food once it gets to the tip area with the more obtuse angle.

In case the wording is unfamiliar, by steering i mean; imagine slicing a large potato, as if you were going to make chips. With a properly 'tuned' knife (be it a a well performing single bevel (100/0) or asymmetric (90/10), or a symmetric ground (50/50) edge) you will get straight cuts of even thickness all the way through the cut. Half way through the potato switch to a right hand single bevel knife like that one...if it's prone to 'steering' your cut will start the same as the rest, but once enough of the blade is in it it will start cutting at an angle. If it "steers into the food" then you would have a slice that's thicker at the bottom on this last cut. Steering away /out would be thinner at the bottom.
The only cure for that would be to sharpen at a lower angle and probably thin the knife at the shinogi. Trying to force a knife like that to cut a straight line will just end up splitting the potato ahead of the blade as the knife wedges into it, more akin to the way an axe splits wood as opposed to cutting it.

I know the level of detail in debating this point is a bit outside of the scope of your original point,  but i think it's a fundamental point that has to be considered before one can claim that theirs is the "right" way... Especially when speaking so adamantly against what was determined to be correct by the manufacturer. Would be interesting to hear from their development team to know if their goal was consistent widths or angles.... I'd be willing to bet its the latter.

Thoughts/comments? Would love to hear more from your side if you have the time to discuss