Laser device for edge angle determination

[Ken S]

Jan, I totally agree. (big surprise )

I think Dutchman's geometrical approach has definitely simplified knife set up. Actually, the principles can be applied to other sharpening. They really shine with knives.

I find the Anglemaster an essential tool, however, I find it clumsy with knives. I prefer to reserve it for uses where it is effective. Having to factor in three degree deviations because a blade is not parallel seems a poor use for a good tool.

Ken

[Herman Trivilino]

This topic brings up my problem with using the Anglemaster with knives. With a chisel or plane  blade, the flattened back presents a large flat surface for the Anglemaster to easily and dependably register. Knife sharpeners do not have this luxury. Knife bevels are tiny, and the larger part of the knife is rarely parallel.

This is an issue I recognized when I bought my Tormek in 2002. Since then I have tried to buy only knives that have parallel sides. For kitchen knives, this easy, but not so for pocket knives.

[Herman Trivilino]

Ignoring the blade V grind results in enlarging the edge angle by the angle of the blade. In the case of the Victorinox knife's the angle of the blade is circa 3° and so ignoring the blade tapering we will ground and edge angle of 33° instead of 30°.

I think you're off by a factor of 2 here, Jan. First of all, my measurements indicate that the blade tapers by 2 mm at a place where the blade width is 50 mm. This is 4% or about 2°. But the error in the bevel angle would be only half that, about 1°.

When I compensate for this I place the knife on my platform jig and measure the angle using the Angle Master. I then remove the knife and again using the Angle Master measure the angle of the platform. The difference between the the two measurements is angle of the blade taper. Half of that is the error in the bevel angle measurement, so I simply subtract that amount.

For example, if I set my platform at an angle of 20°, place my pocket knife on top of the platform, and measure an angle of 24°. The difference is the taper angle, 4°. Half of that is the error in the bevel angle, 2°. If I want to grind a bevel angle of 20° I therefore lower the angle by 2° and set the Angle Master to 18°.

[Jan]

Ignoring the blade V grind results in enlarging the edge angle by the angle of the blade. In the case of the Victorinox knife's the angle of the blade is circa 3° and so ignoring the blade tapering we will ground and edge angle of 33° instead of 30°.

I think you're off by a factor of 2 here, Jan. First of all, my measurements indicate that the blade tapers by 2 mm at a place where the blade width is 50 mm. This is 4% or about 2°. But the error in the bevel angle would be only half that, about 1°.

I do not think I am off by a factor of 2 here, Herman. I think we are in compliance. 

First of all, yours and mine Victorinox knife are different. You have Chef's Knife, 8-Inch long while I have Victorinox carving knife, 6-Inch long with max. blade width some 30 mm. The blade angle of your knife is slightly above 2°, the blade angle of my knife is circa 3°.

Ignoring the blade tapper when using the Knife jig and Anglemaster will result in an increase of the desired bevel angle by the half of the angle of the blade. In my case 15°+ 3°/2 = 16.5°. Thus ignoring the blade tapper we would sharpen an edge angle of 16.5° * 2 = 33°.

To obtain the desired edge angle of 30° we have to set the Anglemaster to (30° - 3°) / 2 = 13.5°.



Your thoughts concerning your platform are correct and well documented by the pocket knife example.  When you would ignore the blade tapering you would get an edge angle of 2 * 20° + 4° =  44°.

Jan

[Herman Trivilino]

I do not think I am off by a factor of 2 here, Herman. I think we are in compliance. 

Yes, you're correct, Jan.

Ignoring the blade tapper when using the Knife jig and Anglemaster will result in an increase of the desired bevel angle by the half of the angle of the blade.

I thought Ken's point in Reply #30 was that the kenjig is immune to this problem!

[Jan]

Yes Herman, the Kenjig is immune to this problem! In the quoted sentence I am mentioning Tormek Knife jig.

Jan

[Ken S]

There is one area where the kenjig has a possible lack of immunity. By design, the kenjig is very simple. Please note that simplicity does not imply any lack of accuracy.

In the design I posted on the forum, the kenjig was set up with a protrusion distance (jig plus blade) of 139mm. Using this protrusion, the distance between the universal support and the grinding wheel is 80mm (using Dutchman's tables) to produce a fifteen degree bevel angle with a grinding wheel diameter of 250mm.

This works well until the wheel wears to somewhere less than 240mm. At 240mm, the distance groove needs to be made one mm longer to 81mm. This is easily done with a small saw. However, the kenjig will no longer be accurate with a new 250mm diameter wheel.

Rich Colvin suggested a very simple, elegant solution for this problem. Rich's idea is to make a set of kenjigs, with distance grooves calibrated for different wheel diameters. Cutting out kenjig blanks is quick and easy. The kenjig is essentially a rectangle of plywood or cardboard approximately 150mm x 30mm (6" x 1 1/4"). Cutting half a dozen requires almost no more time than making one. Cost is minimal. Make a pencil mark 139mm on one side. Cut a groove the thickness of the universal support (12mm) to the length shown in Dutchman's tables)

In Rich's version, make kenjigs calibrated for each 10mm of diameter wear. Mark the jigs with the diameter. Keep out the size which matches your grinding wheel. Put the rest in a drawer. When your wheel wears by 10mm, switch kenjigs.

For those of you like Wootz (and me) who go back and forth between wheels of different diameters, just keep the wheel and jig together.

Thanks for the good idea, Rich. It is a few minutes and a dollar or two well spent. It eliminates the weak spot in the kenjig.

Ken

[Herman Trivilino]

Yes Herman, the Kenjig is immune to this problem! In the quoted sentence I am mentioning Tormek Knife jig.

Jan

So you are! Sorry about that.

[Jan]

Herman, you are welcome.    The Kenjig concept is really immune to the tapering problem provided the blade is properly mounted into the Knife jig. In the past I faced some difficulties with strongly tapered blade of my older Solingen boning knife because the grip of the Knife jig was not sufficient.

Jan

[SharpenADullWitt]

Is the tapering really a problem?  I know forged knives are tapered, but aren't most stamped knives tapered as well, in the manufacturing/grinding process?
What does one need to determine the taper?  Does it come with a Tormek?  (thinking of newbies here)
What about professionals, such as Stevebot?  (time to measure if doing a bunch of knives, etc)

[Jan]

SADW, you can measure the angle of the blade by suitable angle protractor tool and correct the angle set by the Anglemaster.  This can take some 30 seconds.

When you ignore the tapper you will sharpen an edge angle which is by the angle of the blade larger than the desired edge angle. 

Jan

[Jan]

I have redesigned the prototype of my laser goniometer. I have used hand adjustable clamp for smooth  knife alignment and calibrated the scale in bevel angle degrees. The separation between the thick lines of the scale is 5° and between the thin lines 1° of bevel angle.

I have tested Steve suggestion to prepare a semi-circular scale but kept the planar one because its reading is easier and more sensitive. 

Jan

[Jan]

For a knife with optical bevel finish the angle measurement is easy and accurate to +/- 0.5°. For the shown Mora Knife - Tormek Edition the bevel angle is circa 11.5° for both sides. For me it is surprisingly sharp outdoor knife. 

Jan

[Jan]

My oldest granddaughter, who is 14, was tasked to prepare for a physics lesson a short essay on an arbitrary topic from optics. Because she saw my laser goniometer for measuring bevel angles she asked me to lend it to her.

So I still had to make a sketch of how there the laser beam runs. The sketch shows the situation for a 20 degrees bevel angle alpha.

Sorry for the labels in Czech. 

Jan

P.S.: The sketch assumes a flat ground bevel with mirror finish. For hollow grind we get a bunch of reflections where the bevel angle corresponds to the onset i.e. the inner most line of the bunch. For a husky convex grind it is vice versa.

[Ken S]

Jan,

Great project to share with your granddaughter. I expect to learn good things about her work as she completes her education. She is off to a good start with a fine tutor.

I had a little training in fiber optics. (I worked on T1 and T3 data circuits.) What amazes me is how we can simultaneously transmit multiple light frequencies on a single path.

Keep up the good tutoring.

Ken