Sharpening for a better burr

[Jan]

Keeping the edge in contact with the grindstone at the same place is a clever aid, but I hope people aren't thinking it's sufficient for maintaining a bevel angle.

Herman, you have made a very important remark! 

I agree with you and Doug, generally it's not sufficient condition for maintaining a bevel angle.

From grinding practice we know, that we have to pivot the knife as well as lift the handle.

Nevertheless in same cases lifting the handle is not necessary. Imagine for example a semi-circle shoemaker's knife (shown in reply # 50 of this thread). Also the Mora knife shown on my photographs above, requires only slight lift of the handle.

Do you think it is possible to formulate geometrical assumptions under which we can maintain constant bevel angle without lifting the handle?

Jan

[Jan]

No, it's not sufficient by itself, Herman.

But, if I have a projected guideline at a point on the grindstone where holding the knife in a position that naturally feels "level" to me produces a bevel angle of around 18 degrees, say . . . it's a couple of good-sized steps toward sufficiency.   

I did the same thing Jan did, yesterday.  It was easier for me because I had the Bosch laser level to which I posted a link.  Universal support in vertical position, slide on SVD-110 tool rest, clamp laser level to tool rest and adjust.  Kinda overkill for the application, of course, and it would be more elegant to have a focusable laser with an "angle assistant" mounting, but this one puts a very handy, seriously bright line or lines on the grindstone.

I have photos, but I see I need to put them on a server somewhere to share here.  I'll get on that.

I like the laser line.  My old eyes really like it.  It's higher tech than I prefer, but it may be OK to use a bit of high tech to sharpen hand tool edges on a slow wet grinder.   

I'll let someone else play with laser development.  I want to take the one I have and pair it with Herman's knife jig (with a little more clearance between the jig and the stone).

To be clear, the scenario I'm thinking of is essentially farmers market sharpening and variations on that theme.  In the "hybrid" versions of that scenario, as taught by Steve and discussed above by Ken, the Tormek's job might be put a primary bevel on (overwhelmingly) working kitchen knives.  We have to move right along, here, so we won't refine or hone on the Tormek.  Our primary bevel needs to be compatible with the next steps and meet our standards for accuracy and consistency.

I'd like to see if some combination of freehanding and the assistance of aids such as your platform style knife jig and projected laser lines on the stone can produce acceptable and reliable results.

~Doug

Congratulations, Doug!    I agree with you.

I am eager to see your photographs!

You have written: "I like the laser line.  My old eyes really like it. ".

I like the bright red laser line on the grindstone, also. It is really great look at the T7 with this extension. If I wanted to be sentimental and exaggerate, I would say that it reminds me of Moses when he saw the Promised Land. I apologize for the clumsy wording, perhaps you understand what I mean. 

Jan

[Ken S]

I like the "old eyes" comment, also. Even for those with younger eyes, developing a technique less dependent upon frequent remeasurement of the same thing lessens the chance of error. My original motivation for exploring the "knife" setting tool was improved repeatability rather than speed. As a side note, the "knife" part started out as an aid for sharpening chisels.

I don't know if the use of a laser line will end up part of the generally used technique or not. It is possible it will be part of the process along the way. I have a couple prototypes of what is now the "kenjig". I keep them as a reminder of these things being an evolutionary process. Prototypes are important.

Let's keep evolving!

Ken

[Herman Trivilino]

Do you think it is possible to formulate geometrical assumptions under which we can maintain constant bevel angle without lifting the handle?

I think you've already covered this, Jan. Keeping the blue line and the red line equal in length is the necessary condition. But it will require no lifting if and only if the curvature of the blade is the arc of a circle. If it has some other shape, such as a parabola, then lifting will be required to keep the edge on the same point of the grindstone. This will, to a good approximation, maintain a constant bevel angle. If instead you use a platform you avoid all of this fuss and produce a constant bevel angle for any concave shape.

[Jan]

Thank you Herman for your prompt answer. 

I needed to hear your opinion, because my knowledge of space geometry is no more so good to be able to derive it on paper. 

Jan

[Jan]

Because the original topic of this thread started by Steve is "how to use the Tormek knife jigs from the horizontal support to get a larger exit burr", I would like to show that the laser extension can also be used when grinding away from the edge.

In the picture below you can see that the same right angle bent threaded rod can be inserted in the vertical sleeve and the two laboratory clamps will allow to align the laser line on the grindstone.

The knife pivoting must be stopped, when the tip meets the line, otherwise we would grind a larger edge angle at the tip.

Jan

[SharpOp]

Excellent, Jan!

Your photos make clear an idea that occurred to me recently:  that laser line, once it's positioned at the right spot on the wheel, is something of a real-time knife-setting template/positioning guide for Herman's jig.

I've been avoiding setting up a web site for sharpening, but needing a space to host the photos I wanted to share here, I was forced to remember.  I just posted a couple to the waiting skeleton of the site:

http://www.sharpoperator.com/

Now I'll actually have to work on it.   

[Ken S]

Jan, excellent idea switching to the vertical sleeve! First-rate photo, also.

I did some poking around with my Torlock jigs. Although Herman's use of the lower center of gravity scissors jig makes sense to me, I can also see where the regular flat platform jig could be fitted with a thicker platform. (approximately 1/12" or 40mm). That would bring the platform up to the level Steve uses for his freehand technique. It would present a flat (level) platform at the 1 1/2" marked distance from the top dead center mark on the grinding wheel.

I do not know if this would or would be a good idea. It would serve as "training wheels" until someone became comfortable with trying freehand sharpening and possibly a bridge between freehand and jigged sharpening.

Doug: Nice website. I will be following it.  I googled the quote at the bottom. One possibility posed a question and had two possible answers, a furniture store and a credit card company. That struck me as really funny; the world is a marketing op! So, which is the correct translation, buying more furniture or adding yet another credit card?

Keep up the good work, guys. There is much improvement in numbers!

Ken

[Jan]

Excellent, Jan!

Your photos make clear an idea that occurred to me recently:  that laser line, once it's positioned at the right spot on the wheel, is something of a real-time knife-setting template/positioning guide for Herman's jig.

I've been avoiding setting up a web site for sharpening, but needing a space to host the photos I wanted to share here, I was forced to remember.  I just posted a couple to the waiting skeleton of the site:

http://www.sharpoperator.com/

Now I'll actually have to work on it.   

Yes, Doug, I agree with you. 

The major guidance, the laser line can provide, is definitively for freehand sharpening.

Thank you for providing the link to your laser extension photographs. You have found clever and efficient laser mounting. Our approaches are de facto very similar.

Jan

[Jan]

Jan, excellent idea switching to the vertical sleeve! First-rate photo, also.

I did some poking around with my Torlock jigs. Although Herman's use of the lower center of gravity scissors jig makes sense to me, I can also see where the regular flat platform jig could be fitted with a thicker platform. (approximately 1/12" or 40mm). That would bring the platform up to the level Steve uses for his freehand technique. It would present a flat (level) platform at the 1 1/2" marked distance from the top dead center mark on the grinding wheel.

I do not know if this would or would be a good idea. It would serve as "training wheels" until someone became comfortable with trying freehand sharpening and possibly a bridge between freehand and jigged sharpening.

Thank you for your kind words, Ken!

Some sketch or link would help me to understand better your intentions concerning the "flat (level) platform". 

Jan

[Jan]

The photograph below shows, how difficult it is to maintain consistent bevel angle along the entire length of the blade. The knife is correctly mounted into knife jig. This ensures the same bevel angle for the straight part of the blade and for the tip. The belly of the pivoted knife meets the stone beyond the laser line. This means that the belly will have slightly smaller edge angle than the rest of the blade.

In Ken's terminology, to maintain consistent bevel angle, we would need "a bridge between freehand and jigged sharpening".

Jan

[Ken S]

Jan,

You are quite correct; a photo or drawing would be much easier to follow. I will work in that. In the meantime, the link is to a recent posting on the Tormek General part of the forum. The last photo shows a piece of wood clamped to the Torlock jig. In this case, the platform is oriented for the side of the wheel. If you can imagine a shorter piece of wood with an angled end to match the wheel profile located to be centered with the wheel, that is what I mean. By adding thickness, the wood platform could be placed at the height recommended by Steve and kept level. That would allow the knife to lay flat and be at the correct grinding bevel.

I will work on some photographs. Below is a link.

Ken


http://s1340.photobucket.com/user/kb0rvo/media/Kens%20Tormek%20side%20grinding%20platforms/KSTormekjig7_zpsftebqrq9.jpg.html

[Jan]

Thank you Ken, for your explanation and for providing the link to your inspiring photographs. Now I understand better what do you intend.

Jan

[Ken S]

This would be a fine time for grepper to post his digital Tormek again. 

Ken

[SharpOp]

The photograph below shows, how difficult it is to maintain consistent bevel angle along the entire length of the blade. The knife is correctly mounted into knife jig. This ensures the same bevel angle for the straight part of the blade and for the tip. The belly of the pivoted knife meets the stone beyond the laser line. This means that the belly will have slightly smaller edge angle than the rest of the blade.

(Excellent photo illustration here.  Great work, Jan!)

In Ken's terminology, to maintain consistent bevel angle, we would need "a bridge between freehand and jigged sharpening".

Exactly.

I think combining the laser line with a version of Herman's platform "jig" -- a version set up for grinding off the edge -- may be one way to build such a bridge.

. . . I can also see where the regular flat platform jig could be fitted with a thicker platform. (approximately 1/12" or 40mm). That would bring the platform up to the level Steve uses for his freehand technique. It would present a flat (level) platform at the 1 1/2" marked distance from the top dead center mark on the grinding wheel.

Yes.  This is exactly what I've been playing with.

I don't really see this arrangement as a "training wheels" procedure, Ken.  Mostly, that's because I don't think very many people would ever get to the point of grinding as accurate a bevel fully freehand as could be produced using a tool rest and a laser guide line.  Certainly not in our farmers market scenario, with endless variations in knife size and pattern and at least a couple of different primary bevels needed routinely.  I know some sharpeners who tend to think they are as accurate freehand as when jigged, but they are almost always wrong about that.

I think the SVD-110 tool rest is probably the most appropriate base for this.  I've ordered a spare to dedicate to the research.

Now, we need a height-adjustable version of Herman's tool rest knife jig.

Ken, the mystery text is just leftover "greeking" (in Latin) from the default placeholder page when I activated the website.  See: https://en.wikipedia.org/wiki/Greeking.

~Doug