Long Knife Jig asymmetry problem

[Ken S]

Jan, excellent drawing (and thinking). In addition to clarifying Wootz' idea, your drawing also shows more clearly how my angle setting tool works (more more clearly than my description or photo).

Good job!

Jimmy,

I agree completely; we do need more pictures! (perhaps sized a little smaller)

I am working on the situation. In the past year I have retooled from film to digital photography. New camera (Nikon D610); new printer; new film scanner; new "darkroom" (Macbook Pro)and two new lenses. Plus Lightroom CC and Photoshop CC to learn. That's a lot of new tricks for this old dog to learn. To paraphrase you, I'm doing the best I can.

I am working on series of close up photos of knife and chisel edges during stages of sharpening. I am also preparing to demonstrate the Tormek later this month. In addition to that, I have my "day job" of being a caregiver for my two grandchildren.

If Sweden would change my status from volunteer moderator to include part time paid photographer, I would give higher priority to making more photos........

My camera and editing programs are also capable of video work. I believe a short video would make the kenjig very understandable to most of us who seem to have lost our verbal comprehension. Alas, this includes me as well. The constraint with video is me. That's another group of skills to learn. Those skills are on my "to do" list, but not at the top.

Don't stop grumbling.

Ken

[Jan]

Ken, your kind words pleases me. 

There is one practical thing I would like to mention. When we turn the adjustable stop one turn, we shorten the projection length by 2.5 mm (0.1"), which will cause an increase of the bevel angle by 1.5 degrees i.e. enlargement of the edge angle by 3 degrees. This may be a simple guidance for micro bevel sharpening.



Jan

[Ken S]

Jan, excellent thought about the amount of angle chance in a revolution of the adjustable stop screw!

Your drawing describes my angle setting tool "a new angle setting tool" (topic) much better than does my photograph. Would you be willing to copy and modify your drawing by substituting a single bevel (acute enough to provide clearance with the wheel) and post it on the new angle tool topic? The angle tool and kenjig really need a video someday, but, for the present, your drawing is much more clear than my photograph.

Thanks.

Ken

[wootz]

... I concluded that the knife jig is working fully symmetrically for knives which blades are not thicker than about 2 mm.

So, to modify the knife jig for 3 mm thick blades, for maintaining symmetry with respect to flipping, I would remove 0.5 mm from each clamp.

To modify the jig for 4 mm thick blades, I would remove 1 mm from each clamp.

Jan

Hi Jan. The source of asymmetry is that the knife jig has only one adjustable jaw, so the fixed is the one to work on.

[wootz]

There is one practical thing I would like to mention. When we turn the adjustable stop one turn, we shorten the projection length by 2.5 mm (0.1"), which will cause an increase of the bevel angle by 1.5 degrees i.e. enlargement of the edge angle by 3 degrees. This may be a simple guidance for micro bevel sharpening.
Jan

A clever observation, Jan.
I've added it to my collection of Jan's adjustments.

This collection already has your sketch of the knife position in the jig, and this:
"One revolution of the micro-adjust wheel means elevation of the universal support by 1.5 mm (0.06"). This will increase the distance between the support and the stone, and cause that the chisel bevel angle will typically increase by 1 degree."

Much appreciated.

[Ken S]

I second Wootz' comments.

Ken

[Herman Trivilino]

I realized the problem with adjustments every time as the knife is flipped over, is that when I have to alternate sides, it is impossible to maintain strictly the same angle, and because of that I cannot get sharp edge.

How is it that the asymmetry prevents you from getting a sharp edge? I would think it would simply make one vbevel wider than the other, and I can see how that wouldn't be desirable, but I don't see how it could affect sharpness.

[wootz]

Hi Herman, what i was saying is that when I compensate for the bevel asymmetry by rotating the jig adjustable stop every time as the knife is flipped over, it is impossible to maintain exactly the same grinding angle, and therefore get a sharp edge, in a sharpening routine where passes are made alternating the blade sides.
And I alternate the blade sides with every pass in the last, finest, stages, on #4000 SJ and honing leather wheel, where 1 degree difference can dull the formed edge.

[Jan]

Hi Jan. The source of asymmetry is that the knife jig has only one adjustable jaw, so the fixed is the one to work on.

Hi Vadim. Even though it is only one adjustable jaw, the original knife jig design guarantees bevel symmetry for thinner knives. If you filed away 1 mm from the static clamp only, you have disrupted this initial symmetry for thin knifes and not created fully symmetrical jig for thicker knives.

In my understanding, when modifying the jig clamps, we should proceed symmetrically, and remove the same amount of material from both clamps; 0,5 mm for 3 mm blades and 1 mm for 4 mm blades. This approach should ensure the bevel symmetry also for thicker knives. 

Jan

[wootz]

As Goethe said, theory is grey, my friend, but the tree of life is evergreen.

[Jan]

Jan, excellent thought about the amount of angle chance in a revolution of the adjustable stop screw!

Your drawing describes my angle setting tool "a new angle setting tool" (topic) much better than does my photograph. Would you be willing to copy and modify your drawing by substituting a single bevel (acute enough to provide clearance with the wheel) and post it on the new angle tool topic? The angle tool and kenjig really need a video someday, but, for the present, your drawing is much more clear than my photograph.

Thanks.

Ken

Ken, to modify the drawing is not so easy because it was sketched by hand and then scanned, so I cannot change some of the parameters and generate a new drawing.

But if you give me enough time, I'll think how to adjust the sketch for your topic "a new angle setting tool". 

Jan

[Ken S]

Thanks, Jan. anything you can do will be most appreciated. No rush. I wish I had acquired drawing skill; it is a most useful skill.

Regarding removing material from both sides of the knife jig: If we remove enough material from the fixed side to allow the knife blade to be coplanar with the axis of the jig, why do we need to remove anything from the adjustable jaw, the clamping jaw? This assumes the adjustable jaw can be loosened enough to allow the knife to fit and be tightened.

Modifying the knife jig like this would make having an extra jig preferable. Care should also be taken not to remove enough material to weaken the jig.

Fine adjustments for thickness might be made with paper, cardboard or thin pieces of "feeler gage".

Ken

[Jan]

Ken, you're correct.   

In my recommendations, I was guided by the intention that the modified knife jig should provide the same comfort as the original one. Under the comfort I understand margins for the tightening knob and the parallelism of the clamps after tightening the blade. My recommendations are still valid, but are not necessary conditions for proper function of the modified jig.

As confirmed by Vadim, it is sufficient to file away some material from the static clamp only.

Jan

[Jan]

As Goethe said, theory is grey, my friend, but the tree of life is evergreen.

Vadim, thanks for your response through an appropriate quote. Appreciated. 

Jan

[Herman Trivilino]

There can be only one knife thickness for which the bevel angle will be the same on both sides of the knife. A thinner knife will have a wider bevel on one side, a thicker knife on the other side. Thus, it's possible to accommodate a thicker knife by removing some metal from only one side of the jig, but only up to a limit. At some point a knife that's thicker yet will need to have additional metal removed from the other side, too.