Knife tip grinding - To Pivot or Not To Pivot

[wootz]

Yes, Kavik, I've read all you wrote with interest, just to confirm my opinion that this Tormek forum has the most intelligent posters of all forums i know.

Tormek is designed with woodworkers in mind.
As to knife sharpening, Tormek has a potential for precision, but requires inventive approach to materialise this potential.
If you read section on knife sharpening in their first handboook, it is utter absurd.
The only useful bit coming in the following handbooks is about where to clamp the jig.
The rest a knife grinder must invent himself, and learn through pain and frustration.
I am grateful to this forum for shortening my learning curve, but still the only way is through contemplating over the first hundred of f'cked up edges.
But the same can be said all rotary grinders.
In the end you know that Tormek is still the best slow rotary grinder of all available.

[Ken S]

Welcome back, Wootz.

Kavik, I am glad that I am not the only one posting large tomes! Sometimes a thought requires a longer post to be properly explained. I do like your "Cliff Notes" brief summary idea. I will start using it in my future long posts; thanks for the idea.

This discussion reminds me of dovetail saws. Mine is a century old Disston. I would call it the garden variety. The teeth are all the same and the edge is parallel with the back. It cuts well. Everything is symmetrical and pleasingly uniform.

In more recent times, a few sawmakers have drifted from this hallowed balance and began filing finer teeth in the first inch of the sawblade for easier starting. Non parallel edges are making a quiet start. This helps overcome the tendency to lower the angle of the saw and cut more deeply (past the line) on the unseen side if the board. Saw design is becoming more subtle. Most customers would not pay the extra for a custom hand filed sawblade. A few would.

This conversation and similar threads are helping knife sharpening to become more subtle. This is not primarily aimed at the weekend farmers market sharpener who must sharpen a hundred knives in a morning. I do believe the more dedicated of these sharpeners are always wanting to learn more. Some of these tweaks will filter into higher volume sharpening.

If we want our high end customers to appreciate and request this higher level of sharpening, we must not only be able to do this level; we must be able to explain it. Good salesmanship is educating the customer.

I find the versatility of the Tormek fascinating. The Tormek can serve the Mom and Pop occasional sharpeners who sharpen their own kitchen knives, and, perhaps the knives of their local churches twice a year. The Tormek can also handle the busy farmers market trade. It can also cater to the very particular few who demand the very best edges.

I trust these ground breaking topics will continue.

Ken

[cbwx34]

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.

Hey wootz... thanks for responding (glad you didn't mind your thread getting resurrected).

Doesn't Jeff's video basically support your "no need to pivot" position (for most knives at least)?

I also think that, in addition to where the knife is on the stone in relation to the support affecting the angle... the relationship of the belly/tip becoming more of a "side angle" (what I described earlier) also affects it.  This is another reason why the placement of the knife in the jig is so important.  (There has been a lot of discussion on other guided sharpeners... on how the angle can change in the "belly to tip" area... based on how the knife is clamped in relation to the pivot point... and can change quite dramatically once the blade starts to curve).

Basically, I think that, if you're going to pivot the knife... setting the knife in the jig so it maintains the same line (or point) on the stone is important... if you lift the handle, you set the knife in the jig to maintain the angle as the relationship of the knife to the stone changes... not only in relation to the line on the stone... but as the angle "rotates" to the side.  And, as you stated in your original post... different shapes/types of knives require a combination of these, or even a modification to achieve the desired result.  (Sharpie is your friend).

[Ken S]

Wootz' last post came in while I was typing. He makes some interesting points.

I believe the Tormek is evolving. Rich has called me the Tormek Historian, with some justification. I find the development of the Tormek fascinating. I agree with Wootz that woodworking tools have been a primary focus. I consider the new 186 gouge jig and the TTS-100 setting tool the present pinnacle combination. For accuracy, repeatability and versatility, this duo leaves most off the other jigs, including all the knife jigs in the dust at the present time. The 90° registration fence of the SE-76 and controlled camber of the SE-77 are certainly giant steps forward. The DBS-22 drill bit jig is a marvel. The TT-50 truing tool and microadjust are advances.

I believe we will see similar advances in knife jigs. A knife jig should be self centering for thickness variations. I think we should have interchangeable stops, with and without the radius. We should remember that we are among the more picky of the Tormek customers. In recent years, I have developed the belief that Sweden is actually reading our posts and giving us some attention. This seems win-win, both for us and for Tormek.

I believe the Tormek is capable of more than is usually expected with our present jigs. We keep evolving.

Ken

[Jan]

Hello Wootz, I like to hear from you again!

Kavik, I have enjoyed your content-rich posts! Very good food for thought. In some cases I need some time to digest it.

CBWX, thanks for starting the useful site: Knife Sharpening on the Tormek.

Ken, you have compiled an interesting list of potential jig's improvements.

Jan

[cbwx34]

CBWX, thanks for starting the useful site: Knife Sharpening on the Tormek.

Jan

Thanks.  It's definitely a "Work In Progress"

I believe we will see similar advances in knife jigs. A knife jig should be self centering for thickness variations. I think we should have interchangeable stops, with and without the radius. We should remember that we are among the more picky of the Tormek customers. In recent years, I have developed the belief that Sweden is actually reading our posts and giving us some attention. This seems win-win, both for us and for Tormek.
...
Ken

Well, if they are listening... self-centering is at the top of the list for me.   Like you, I agree that the Tormek's strong point is primarily woodworking related tools... but also think it's a great knife sharpener... it's just often overlooked, and it's advantages (for example water cooling), is not properly utilized (if that makes sense).

[Kavik]

Thanks all for the interest and the kind words. It's always a risky proposition to be a new guy on a forum questioning existing posts lol glad to find a place that's open to discussion like this

In the end you know that Tormek is still the best slow rotary grinder of all available.

I won't argue that it seems to be an incredibly well built machine. And what it does, it does quite well! As Ken said, a lot of the newer jigs seem to be leaps and bounds above their older counterparts.
But I'd agree that it is better suited for tools than knives.

In a perfect world I'd have a horizontal water wheel for those. A flat surface that leaves flat bevels as opposed to concave ones.
But let's face it, as expensive as the tormek is, those horizontal setups can be 2-3x the cost, are just about impossible to contain the mess in, and would be best suited to having a permanent work area set up for them... Not great for going out and sharpening for others. If I were making knives, or had a business where I had to often reprofile knives and could justify the cost, that's what i would own. And the tormek would stay for the woodworking tools

Everything in life is a trade off though. For many that means going with the speed and ease of the tormek, which is fine in many cases... But in my case, my Japanese kitchen knives will continue to be used with the water stones, not the water wheel.
They're just too finicky for this sort of a system, the entire blade needs to be considered as a whole, not just the actual cutting edge.
If anyone is interested in learning more about it, a great place to start would be "Japanese Knife Imports" youtube channel. Jon, the owner there, is a great guy. Very knowledgeable and extremely helpful. I've dealt with him many times for both questions and purchases and have always been satisfied.

Again, not trying to take away from the tormek here, but every system has it's limitations. If i were doing this as a business I would be studying as much as i can about the different style knives, and how they are traditionally done by hand, to determine if a grinding wheel is an acceptable alternative so i would know what to say when a customer brought one to me

[Herman Trivilino]

It seems there are two conflating issues about knife blade geometry being discussed here. For a knife with symmetric bevel angles there are two factors to consider.

1. If the cutting edge is not centered the bevel width on one side of the knife will not match the bevel width on the other side.

2. If the knife is thinner at the tip, then either the bevel width or the bevel angle, or both, will be different at the tip than elsewhere along the edge.

The only way to center a cutting edge is to grind more steel away from one side of the knife.

I agree that knife sharpening seems to be secondary to tool sharpening for the Tormek design.

[cbwx34]

It seems there are two conflating issues about knife blade geometry being discussed here. For a knife with symmetric bevel angles there are two factors to consider.

1. If the cutting edge is not centered the bevel width on one side of the knife will not match the bevel width on the other side.

2. If the knife is thinner at the tip, then either the bevel width or the bevel angle, or both, will be different at the tip than elsewhere along the edge.

The only way to center a cutting edge is to grind more steel away from one side of the knife.

I agree that knife sharpening seems to be secondary to tool sharpening for the Tormek design.

I would add "thinner or thicker at the tip".  Many knives appear thinner, but the belly/tip area actually moves into a thicker part of the blade... depending on how it is ground.  (The width and/or angle will still change... but in the opposite direction).

While sharpening knives may be secondary... if you look at the "stats" of the forum, and eliminate the "General Tormek Questions" section... the "Knife Sharpening" section is only 88 posts (now 87) shy of equaling all the other sections combined.  So, the interest certainly appears to be there.

[wootz]

Hey wootz... thanks for responding (glad you didn't mind your thread getting resurrected).

Doesn't Jeff's video basically support your "no need to pivot" position (for most knives at least)?
....

OMG, with knife that long and where he clamped it in the video, the tip SHOULD be pivoted towards yourself, or you will grind off the tip; other solution is to clamp closer to the tip, not at the centre.
I have all my respect to Jeff, he is a talented presenter - don't take this video as educational, it is 'advertorial' (not sure is this is a right word), but was never meant to be instructional.
I haven't had time yet to watch DVD that Ken mentioned, coming with T8, maybe some hints are there.

[cbwx34]

OMG, with knife that long and where he clamped it in the video, the tip SHOULD be pivoted towards yourself, or you will grind off the tip; other solution is to clamp closer to the tip, not at the centre.
I have all my respect to Jeff, he is a talented presenter - don't take this video as educational, it is 'advertorial' (not sure is this is a right word), but was never meant to be instructional.
I haven't had time yet to watch DVD that Ken mentioned, coming with T8, maybe some hints are there.

May not be ideal where the clamp was placed... but moving the clamp closer to the tip will increase the angle, resulting in a greater chance of grinding the tip off... not the other way around.  For the knife in the video... shouldn't be much of an issue where the clamp is placed... it's not a lot of change.

I think Jeff's video is designed to be an instructional video more than just an advertisement... there's too much detail.  My .02 anyway.

[Jan]

Some blades can be sharpen from heel to the tip with no need to pivot while other blades with no need to lift the handle.

Based on my limited experience, the compromise between lifting and pivoting is the suitable approach.

Because it is crucial how the blade is clamped in the jig, some two years ago, I have prepared simple "Knife Tip Settig Template" for kenjig projection length of 139 mm. https://forum.tormek.com/index.php?topic=2654.0

This clamping guarantees that you will get the same bevel angle at the heel and at the tip, more or less with no need to lift the handle. The template is not a universal tool, it works fine only for limited set of blade shape's.

Wootz has shown several examples for which this approach does not provide consistent bevel width.   

Jan

P.S.: The template design was extracted by back engineering the radius of the adjustable stop of the knife jig.

[Kavik]

Jan,
Just to clarify, the above template setup is intended to work in conjunction with the idea that you should maintain the same line of contact, correct?

[Jan]

Yes Kavik, you are correct. If it is possible that the edge meets the stone along the same line of contact, than the bevel angle should be the same along the entire edge.

When some part of the belly is above the red circular line of my template (goes beyond the line of contact), than it is necessary to lift the handle here to achieve the same bevel angle along the belly also.

Jan

[Jan]

My friend from local knife.cz forum prepared wooden version of my template. I like it. The knife jig is guided and your hands are free to clamp the knife properly. 

Jan