Author Topic: We need the Bevel protractor  (Read 1656 times)

Offline Sharpco

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We need the Bevel protractor
« on: January 17, 2019, 08:09:06 am »
When setting the angle of kitchen knife with AngleMaster, everyone assume the bevel is 0 degree.

But it's not.

A few days ago, I got a bevel protractor and checked it.

Chef knives: 1.5 dps
Pairing knife: 2.3 dps

The problem is that we can't measure this acute bevel angle with AngleMaster.

Do you want to set the edge angle precisely with AngleMaster? You need a bevel protractor.

Offline GKC

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Re: We need the Bevel protractor
« Reply #1 on: January 17, 2019, 10:37:08 pm »
I have a feeling that this has been discussed before, but here is how I deal with the issue.

Most blades are tapered from the spine to the secondary bevel (or right to the edge in a full flat grind), and so I agree that registering the AngleMaster on the face of such a blade will not result in the blade being sharpened at the angle indicated on the AngleMaster.  I use one of the following fixes, each of which can be used in a pinch without a bevel protractor:

1. If you have a typical kitchen knife, adjust the angle that you set on the AngleMaster (add about 3 degrees on the AngleMaster), or

2. If you can't make a reasonable guess at the degree of the taper, use a flat "proxy blade" in the knife jig (e.g. a flat piece of metal or a credit card) to set the angle (at the exact desired grinding angle), then put the knife in the jig.

Gord

Offline Ken S

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Re: We need the Bevel protractor
« Reply #2 on: January 17, 2019, 11:30:02 pm »
Sharpco, Your Mitutoyo Bevel Protractor is a fine precision tool,measuring to five minutes of arc (1/12 of a degree). Like Gord, I made a "substitute target" (same concept, different words).

For measuring angles, you Mitutoyo tool is the head of the class.

Ken

Offline Sharpco

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Re: We need the Bevel protractor
« Reply #3 on: January 18, 2019, 02:25:57 am »
I have a feeling that this has been discussed before, but here is how I deal with the issue.

Most blades are tapered from the spine to the secondary bevel (or right to the edge in a full flat grind), and so I agree that registering the AngleMaster on the face of such a blade will not result in the blade being sharpened at the angle indicated on the AngleMaster.  I use one of the following fixes, each of which can be used in a pinch without a bevel protractor:

1. If you have a typical kitchen knife, adjust the angle that you set on the AngleMaster (add about 3 degrees on the AngleMaster), or

2. If you can't make a reasonable guess at the degree of the taper, use a flat "proxy blade" in the knife jig (e.g. a flat piece of metal or a credit card) to set the angle (at the exact desired grinding angle), then put the knife in the jig.

Gord

Hello Gord,

1. My chef knives have main bevel of 1.5 dps. So I have to set +1.5 degrees on the AngleMaster. The problem is that the bevel angles of all kitchen knives are not the same.

2. Using proxy blade is a good idea. But thicker blade is clamped asymmetrically in the knife jig. So we need exactly same thickness of the proxy blade.

Offline Ken S

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Re: We need the Bevel protractor
« Reply #4 on: January 18, 2019, 04:09:57 am »
I would only use the Anglemaster with the proxy blade (substitute target) because it is on a parallel plane with the knife jig. The proxy blade should project the same length from the jig as the actual knife blade.

I sized my substitute target to match the thickness of the milled area in the knife jig. That keeps the jig and the knife in the same plane. If you sharpen a variety of knives, you may need several modified knife jigs and substitute targets. Wootz uses four knife jigs for different thicknesses.

Ken

Offline Drilon

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Re: We need the Bevel protractor
« Reply #5 on: January 18, 2019, 07:50:29 pm »
Why don't you use Knife Grinders (wootz) software to set the correct angle? It is easy to use and very precise.

Offline Sharpco

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Re: We need the Bevel protractor
« Reply #6 on: January 18, 2019, 09:54:02 pm »
Why don't you use Knife Grinders (wootz) software to set the correct angle? It is easy to use and very precise.

I have it. The problem is that SVM-45 can't clamp blade symmetrically. So I have to set the angle both side. If someday, tormek makes self-centering knife jig, then I'll not need it.

Offline Ken S

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Re: We need the Bevel protractor
« Reply #7 on: January 19, 2019, 12:03:09 pm »

I have it. The problem is that SVM-45 can't clamp blade symmetrically. So I have to set the angle both side. If someday, tormek makes self-centering knife jig, then I'll not need it.


Your statement is not quite accurate. The fixed jaw has a 1.25mm machined slot designed to center a 2.5mm thick knife blade. This is a typical thickness for many contemporary kitchen knives. At this thickness, the jig is self centering. As the thickness of the knife blade deviates from 2.5mm, a symmetry error is gradually introduced. I leave it up to the individual sharpener to decide how critical this error factor might be. I can see where it might be a consideration with a premium priced sharpening of a very expensive knife.

This kind of high precision sharpening seems outside of the operating cost model for everyday sharpening. If a customer wants this level of sharpening, and is willing to pay a premium for it, then I think the sharpener, like Wootz, should be equipped with several knife jigs custom machined with different slot thicknesses and shims. I do not think it is reasonable to expect this level of precision workmanship for standard prices.

On the other hand, this variation in symmetry is not necessarily bad. Magnus has posted about Japanese knives having different bevel angles to favor the dominant hand of the user. I am left handed. I reground a santoku knife to a single left handed bevel. I probably overdid it, however, the knife works very well for making very thin slices of apple and cheese. Depenfing on which side of the blade was placed in the milled slot of the jig's fixed jaw, the handedness of the user could be favored. I would not use this for everydsy sharpening, however, it might have possibilities for  infividual high end customers.

Like many of us, I look forward to redesigned knife jigs, however, I think the self centering issue with the present jigs is overblown.

Ken