Angle Logic!

[Chris]

Trying to get my head around how I mount and setup tapered knives to achieve a bevel of the same width on each side.
By tapered, I mean a knife that doesn’t have sides parallel to each other where the WEPS clamps.
A wide spine with flat sides evenly tapering to a thin edge, then a bevel.

This picture (although not taken for this purpose) shows a correct illustration of angles being the same on each side.

But it uses a rectangular blade.

Of course it would still be the same if you were able to clamp a tapered blade in a perfect vertical plane, but the WEPS has trouble doing this.

As the left side of the clamp always remains fixed and perpendicular to the angle bar, it pulls the left face of the knife against it when clamped, while the right side of the clamp adjusts outward to achieve a tight grip on the knife face.

If you look under the clamped knife (between the left and right clamps) you will see a gap that tapers from narrow at the top to wider on the bottom.
Fine, you say, it’s a tapered blade?
You should also notice the right clamp is protruding out some distance at the bottom, no surprises once again?
But this also means the knife is angled to the left, if you look along the blade from the handle you can see this.

Now, if I set my angles to 20Ëš on each side with my angle guage, (like every one does) I will get a narrower bevel on the left side.
Even though I will achieve a correctly angled edge.

The only way I can see to obtain my goal is to somehow make the knife perfectly vertical in the clamp or deliberately have different angles on each side.
To get 20Ëš with even bevel, then perhaps I need 19.5Ëš on the left (less) and 20.5Ëš on the right (more)?
I’m guessing smaller changes would apply.

How to I calculate this while a knife is clamped?
Has this already been discussed somewhere before?

Should I just go outside and smell the roses instead? 😉

[Mark76]

I don’t quite understand the problem you describe. If the problem is that the knife isn’t perfectly vertical in the vise, try to clamp it using a piece of chamois. (Chamois? According to my dictionary this is an animal :-). I mean the soft leathery stuff.)

If the problem is that the knife is quite wide and that the right clamp protrudes to the right so much that the angle bar doesn’t indicate the correct angles anymore, use an angle cube.

If it’s yet another problem, please explain :-). Smelling roses is always a good idea. (Man, it’s getting winter where I live, almost freezing outside. Lucky you.)

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Chris]

I don’t quite understand the problem you describe. If the problem is that the knife isn’t perfectly vertical in the vise, try to clamp it using a piece of chamois.

That’s basically the problem, I would need to put chamois on the left side only and guesstimate. 😉

[Mark76]

I still don’t quite get it. The idea of chamois is that it is quite flexible and that it compresses at points where needed and not at other points. So it helps in getting a fully flat ground blade vertical. Foam tape might help, too. I use that myself. See here.

Why would you need to put chamois on the left side only? Or is the problem that your knife tapers only on one side?

Which shape does your blade have?

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Chris]

Apologies, I will need to post some sketches to explain.
Not in a position to create those at the moment.

The left side of the clamp is perpendicular to the crossbar, and remains that way.
The right side is not when clamping a tapered (triangular) knife.

Left Side!

Right Side!

[Chris]

I added some “slightly exagerated” pics.
You see the gap against the blade on the right?

How can the knife be located vertically, perpendicular to the crossbar?
Central, evenly,

[Mark76]

I see. The knife is simply not straight in the vise. Foam tape or chamois should really help you, I think. Why doesn’t it work?

Big knives can pose other challenges (and it looks like a big knife), but there’s…

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Chris]

So I pack it with foam tape and look along the edge?

[Mark76]

Yeah. Only at the top of the vise, so the knife remains vertical. Clay explained it here.

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Chris]

Perhaps Clay can comment on this one?

That link seems to be for a different purpose?

[Phil Pasteur]

Not sure if you did it just to emphasize the problem, but your bottom screw is definitely cranked in too far.
I try to start with the knife sitting in the vice and the inside surfaces of the vice being parralell. I do put blue painters tape on the blade and use a piece of Chamois or the soft kind of medical gauze wrapped all of the way around the spine of the knife and extending towards the edge of each side well past the tips of the jaws on both sides, this gives a layer that can be compressed at the spine but still gives support to the tapered sides of the knife. I then tighten the top screw down hard while making sure the blade is centered. Then I tighten the bottom screw, but no more that I have to to keep the knife from movingj, just snug. I try to keep the gap between the fixed and movable vice jaws equal top and bottom. The only time I ever saw my vice look like your pictures (pushed out that far at the bottom) was when I had bent the tip on one side of my vise.

Anyway, after I do things as described above, I get virtually identical bevels. Using the proper technique, you too can get that blade pretty close to dead on centered!!

Phil

[Mark76]

Not sure if you did it just to emphasize the problem, but your bottom screw is definitely cranked in too far.

That’s a good point. First tighten the top screw, only then the bottom one.

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Phil Pasteur]

That link seems to be for a different purpose?

Hmmmm. I looked at the info that was linked. It was pretty specifically about how to properly clamp a FFG (triangular) blade in the WEPS properly. Isn’t that what you want to be able to do?

What other purpose did you think it was for?
Phil

[Chris]

Not sure if you did it just to emphasize the problem, but your bottom screw is definitely cranked in too far.

That’s a good point. First tighten the top screw, only then the bottom one.[/quote]

I always do, is there another way?

The top screw sets the clamp angle and the bottom tightens the grip.

I pinch the clamp from above to match the blade angle on both sides, then bring the top screw in to gently hold that grip.
Then tightly secure it all with the bottom screw, which spreads the clamp out at the bottom and therefore in at the top.

Is this wrong?

edit – Can I suggest you kind people try this, you will see the knife leans to the left?
It’s no surprise, I’m just trying to work out the best way to counter this so I get an even bevel.
Not angle, bevel width the same on both sides.

[Mark76]

Is this wrong?

No, that sounds right. But I still don’t understand your problem :-).

Molecule Polishing: my blog about sharpening with the Wicked Edge

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