Messages

It is said that swords were sharpened in this way in the Middle Ages.

Jan

Rich, I find even more interesting the old picture displayed on your Sharpening handbook site. http://www.sharpeninghandbook.info/indexAbout.html
The grind stone is not a wheel but an oval shaped grind stone. It is said that the supervising man commands the axe grinder to hold the axe so that the resulting grind is convex.

I studied it on a simple model, but it remains a riddle for me.
https://www.dropbox.com/s/6uquqq1gkoyptrw/OVAL%201.jpg?dl=0
https://www.dropbox.com/s/amvas2zqyg0yffc/OVAL%202.jpg?dl=0

Jan

Gilles, in my understanding the condition for minimum grinding angle is, that the chord length is the same for both wheels. In your example the chord length is 11.4 mm. Also the angle of the chord will stay the same (15.3⁰) for both wheels.

CB, you are quick! 

Jan

Chord angle = ( grinding angle + heel angle ) / 2

Jan

Gilles, welcome to the forum!

Thanks for sharing with us your very nicely done Excel spreadsheet. It is well documented with formulas and drawings and it covers wide span of tasks related to the geometrical aspects of sharpening. I find it valuable and inspiring.

I have validated your page "USB height" and can confirm that it works accurately!

My comment to this page is, that many people use the USB top to stone distance for setting the grinding angle. It is machine independent value.

Your "Polishing angle" page, reminded me the central angle theorem which relates the grinding angle, chord angle and heel angle. Your values are in compliance with this theorem.

Jan

Rick, thanks for your clarification. Your idea "width of marker removed" is very interesting.

I was talking about using marker lines as tiny ink "shims" with a thickness of some 2 or 3 microns.

Jan

Rick and Jan,

Good comments; thank you. I do not take offense with your comments about the kenjig. The present jig is the most recent of several generations of prototypes. If it remains the most recent generation for several years, we are not doing our jobs. We need to continue evolving.

I based the kenjig on Dutchman's tables. This was well before Wootz' pioneering work on deburring. Jan, your point is well taken. Based on your comment, I think it makes sense to switch kenjigs every five or six millimeters. I make the present kenjigs out of baltic birch plywood, using my table saw and bandsaw. The set up is quick and easy. I usually make up several at a time as gifts. Making separate kenjigs for every five or six millimeters would not be a problem.

I sharpen my own cooking knives. My simple methods are quite adequate. If modifying things can make adequate better, I will choose better.

Ken

Ken, thanks for your understanding. You know that I am large fan and user of kenjigs. The angle accuracy 0.25⁰ is really a very good result and 6 mm loss in diameter is still acceptable switching interval for kenjigs. The accuracy 0.25⁰ is necessary only for advanced deburring methods.

If you are honing freehand, as recently shown in Tormek Live Sharpening Class you of course do not need grinding angle accuracy 0.25⁰. For freehand honing it is fully sufficient to switch to another kenjig each 10 to 12 mm ( ≈ 1/2") loss in stone diameter.

Jan

[IF]

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A useful angle setting method should be robust which means that it should have the ability of tolerating common errors in input parameters. In my understanding the setting should result in angle accuracy of some +/- 0.25⁰. When the desired grinding angle is 15⁰ than the real angle will be between 14.75 and 15.25⁰. Similarly when the desired honing angle is 16.5⁰ than the real angle will be between 16.25 and 16.75⁰. If we consider the least favourable combinations we will hone at an angle which is 1 to 2⁰ higher than the grinding angle. This will probably allow successful deburring.

When the angle setting accuracy drops below +/- 0.5⁰, successful deburring is not guaranteed, because the honing angle increase may be too small.
...snip...

This is interesting and I tend to agree with you, only based on my hands on experiences.  It causes me to wonder about the sensitivity of the black marker method of estimating angles, IF one were to carefully study the nuances of where and how much on a bevel that the marker is removed, revealing where the grinding/honing is occurring.  I do not suggest this as a potential substitute for precision angle setting.  Only as a curiosity.  Gradations of where and how much marker is removed certainly reflect differences in angles and granted, may be too gross to be of any practical use.  I'm too busy to spend any time exploring this, just an associated passing thought. 

P.S.: Rick, I am not sure what is your Go Calc app, but assume that it is the Knife Sharpening Angle Calculator coded by CB. I have validated this calculator, it uses the exact formula and works fine. It should provide the same figures as in my charts. I am mentioning it because some apps offered on this forum use the older, approximate Ton formula and are not fully suitable for advanced deburring procedures.

Yes, CB's GoCalc.  I checked it against angles generated in TormekCalc 2 and they were withing 0.02mm, which I regard as irrelevant, primarily since I am not concerned about the exact angle, but rather the relative consistency between wheels and operations.  Using the same app should maintain that consistency.  As I understand it, you (or someone) has validated that TormekCalc2 generates accurate values as well. 

Rick

Rick, I have read somewhere that the thickness of black sharpie line is some 100 millionth of an inch. Red line should be thicker.

Yes, I have validated the TormekCalc2 it generates accurate values. The 0.02 mm discrepance generated by CB's sw is negligible.

Jan

Getting back to the real world, I do not think we need many kenjigs for everyday use. Many of us standardize on one or two standard bevel angles. Eventually, I believe diamond or CBN constant diameter wheels will become the standard, eliminating much of the need for wheel diameter compensation. In our present environment, I realize that our farmers market members actually do wear out SG or SB grinding wheels. However, most of us will go a long time before wearing down our grinding wheels from 250 to 240mm. In my opinion, for most of us, a ten mm loss in diameter is a good time to either modify the kenjig by making the Distance groove one mm deeper or switching to another kenjig. Four or at most five kenjigs should suffice for the useful working life of a grinding wheel used for knives.

Ken, when we switch to another kenjig each 10 mm loss in diameter than the grinding angle accuracy will be slightly better than 0.5⁰. It is a very nice result for common knife grinding.

Nevertheless to achieve an angle accuracy 0.25⁰, necessary for advanced deburring procedures, it would be necessary to switch to another kenjig each 6 mm (1/4") loss in stone diameter. For this reason I modified the combination square shown above which serves me as an adjustable kenjig.

Jan

Ken and Rick, full analysis of errors on setting for a desired bevel angle would be a difficult task. It is clear that we have to measure the projection distance, diameter and USB top to stone distance accurately. But this is not sufficient because the blade should be mounted symmetrically into the knife jig also.

A useful angle setting method should be robust which means that it should have the ability of tolerating common errors in input parameters. In my understanding the setting should result in angle accuracy of some +/- 0.25⁰. When the desired grinding angle is 15⁰ than the real angle will be between 14.75 and 15.25⁰. Similarly when the desired honing angle is 16.5⁰ than the real angle will be between 16.25 and 16.75⁰. If we consider the least favourable combinations we will hone at an angle which is 1 to 2⁰ higher than the grinding angle. This will probably allow successful deburring.

When the angle setting accuracy drops below +/- 0.5⁰, successful deburring is not guaranteed, because the honing angle increase may be too small.

From this example it is clear, that free hand honing cannot deburr the blade with sufficient accuracy. For a common customer the blade will be probably sufficiently sharp, but under the loupe we often see that it was not fully deburred or was dulled.

Jan

P.S.: Rick, I am not sure what is your Go Calc app, but assume that it is the Knife Sharpening Angle Calculator coded by CB. I have validated this calculator, it uses the exact formula and works fine. It should provide the same figures as in my charts. I am mentioning it because some apps offered on this forum use the older, approximate Ton formula and are not fully suitable for advanced deburring procedures.

Ken, attached you will find the extended chart in two resolutions.

Jan

CB, thanks for your response and good recommendations.

You are correct that for T4 and T7/T8 the blue line in the chart could be reduced to two blue points. In my view the blue line may be good for people using paper or felt wheels for deburring. Those wheels are sometimes slightly larger than 250 mm. I will change the blue line to a dotted line and mark the diameters of both Tormek honing wheels.
Thanks for the diameter of LA-145.

The diameter of LA-220 is some 215 mm. In my understanding it was done by Tormek intentionally to make honing angle automatically higher than the sharpening angle. When you set the honing angle with WM-200 and point the diameter compensator to LA-220 you will get a honing angle which is by some 1.3 ⁰ higher then when the compensator points to the real honing wheel diameter 215 mm. (When the sharpening angle was 15⁰ than the honing angle will be some 16.3⁰.)

Jan

Drilon, CB, yes, the main reason for the chart was to have all possible kenjig dimensions on one sheet of paper and not on many pieces of paper. You surely know the situation when the real stone diameter is smaller than the one used for your kenjig. You are then often procrastinating to cut new kenjig and compromise the consistency between sharpening and honing angles.

I am not always cutting new kenjig from a set of pre-prepared kenjig blanks. I use also my modified combination square to set the USB height. That was the reason for printing also some figures in the chart.

I use the chart also to set the angle on my new belt grinder with 250 mm contact wheel. Some grinding belts are thin (0.5 mm) but some honing belts are thick (3 mm). Such a diameter increase has to be reflected in the setting otherwise you may happen not to be able to deburr the blade correctly.

Jan

Ken, yes, the chart can be extended towards smaller stone/wheel diameters.

Please let me know the real diameter of LA-145 honing wheel.

Jan

My favourite angle setting tool for kitchen knives is kenjig with projection distance 139 mm. My standard bevel angle is 15 dps. The attached chart shows in red the change in distance from the grindstone to the top of the USB for the whole lifespan of the grindstone. It starts at a distance 78.9 mm for 250 mm diameter and ends at a distance 89.3 mm for a fully worn grindstone (180 mm).

My standard deburring procedure consist of honing at the leather honing wheel at an angle 16.5 dps. The chart shows in blue that for leather honing wheel LA-220 with 215 mm diameter the distance from the wheel to the top of the USB is 85.7 mm.

Because my computer is situated two floors above my shop this chart reduces my movement on the stairs between the basement and the second floor.

Jan