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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.

Thanks for posting this.  Very helpful.

I think your template also illustrated why I feel the jig radius doesn't 'feel' quite right, and why Wootz found it didn't work for the knives he was sharpening, (and as you stated only for certain blade shapes).  If you look at the attached picture, you see the clamped knife doesn't fit the radius unless the knife is moved, which equals the the projection length being shortened if I'm 'reading' it right.  (So perhaps Wootz could have got it to worked if he had altered the projection length?)

(One thing I've learned in dealing with other guided sharpeners with a pivot... it's a little more complicated than it first appears). 

Your template is a good reference though... definitely helps define the process of what is going on. 

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.

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.

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).

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).

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.

Several years ago, Ionut, a very experienced forum member, posted about the gap. His solution was to place an electrical cable tie through the hole in the TT-50. He posted a lengthy explanation.

I had not experienced this difficulty, however, as I regard Ionut highly, I placed a cable tie on my TT-50. It eliminated the gap. I had the tie on for several years before removing it. For me, the TT-50 seems to work with or without the tie. If I ever encounter the difficulty, my first line of defense will be to place a tie.

Ken

Here's the ionut post I believe...

https://forum.tormek.com/index.php?topic=1077.0

(I usually track down referenced posts to learn more... figure might as well post 'em if I find 'em).

Yes, that's it.

Anyone listen to the podcast... Knife Talk?  A guy who chats with different knifemakers for ½ hour or so.

(Oh yeah... it's sponsored by Tormek). 

With all this "truing" talk  ... it made me take a close look at my stone.  I keep it in pretty good shape using a DMT XXC stone (braced against a USB... works pretty good, at least for knife sharpening), but had a couple of spots a bit out of whack... so decided to use the Truing Tool (old version), and clean it up a bit.

Worked fine, but wanted to point out that after truing and grading the stone fine, I remarked the stone with the angle markings... but noted that the old markings were still faintly visible (see attached pic... also made the marks a bit more accurate).  Thought it was a good indicator that if the stone is kept in decent shape... very little material is actually removed in the truing/grading process... (it seems like a lot in the water  ).  (I'm sure a bit of Sharpie soaks in... but doubt it's very much).  Just thought it was an interesting observation.

Hatchcanyon.... very nice, and some good ideas.

I've been thinking of motorizing my TT-50 truing tool.  The thinking is that it would allow it to run slower (I sometimes get impatient and run it too fast). It would make it run consistently, and I can enjoy a cup of coffee whilst it runs ("Look ma, no hands!").

Rich

That sounds pretty cool!

(Bonus points if you can get it to run a sharpening jig back and forth)... 

The truing tool is one thing I'm still getting frustrated with.... I'll get half way through the wheel with no problem, then the other half chatters so much it leaves patterns in the wheel, forcing me to take another pass and waste more stone 

I've tried going lighter passes, deeper passes, faster, slower.... Can't figure out what the common denominator is when it decides to do it and when it decides to work fine

You might take a look at this thread... has some tips that could help.

https://forum.tormek.com/index.php?topic=1353.0

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.

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.