Chart for kenjig dimensions

[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

[Drilon]

Hello Jan, this graph is great. Thank you!

[Ken S]

Jan, Well done and informative chart.

I have two suggestions:
1) Could you either extend the diameter range or make a separate chart for the T4? The wheel diameter range should be 200 to 150mm, and the leather honing wheel diameter 145mm. This would be useful for T4 users.

2) I would suggest adding a log by date. The log entries should include the date used and the grinding wheel diameters.

Thanks,

Ken

[cbwx34]

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

Nice chart.

So... you use it when you want to build another Kenjig?

[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

[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

[cbwx34]

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

Thanks for the clarification... I kinda figured it had moved beyond the kenjig concept... although can be used for that of course.

One suggestion, since you've been asked to make it for the T-4 too... maybe change the blue line, to a blue point, since the leather wheel never changes?  My thought is someone who finds this later, without fully understanding the concept, might get confused by the line on a wheel that doesn't change size.

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

It's actually measures about 146mm... but unlike the LA-220, I don't think the difference is intentional... I'd probably go with 145mm.

[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

[Jan]

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

Jan

[Ken S]

With all of the discussion of various methods of setting grinding bevels for knives, I have not seen much discussion of one critical element: How precise do we need to be? In the machine shop/tool and die making world this is called tolerance. The related question to this is how accurately can we measure?

Our trig based programs can produce extremely precise answers, far more precise than we require or can measure. Our measurement tools fall far short of this precision, even high quality tools from world renowned manufacturers such as Starrett. In fact, the humble kenjig is based on gage blocks, our most accurate metal measuring tools. Gage blocks can be far more accurate than digital calipers. The kenjig could be made of ground hardened tool steel or carbide and be made accurate to several millionths of an inch. This accuracy would require the operator to wear gloves in a temperature controlled 20° C. laboratory and special diamond wheels. It would cost several thousand dollars and be completely ridiculous.

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.

Incidentally, when I think of the "kenjig concept" I always think of it as an application based on the pioneering work of Ton Nillesen, "Dutchman" on the forum. The concept belongs to Ton; I only adapted Ton's work to my needs.

Ken

Jan, I like your chart.It is straightforward and practical. Like you, I keep my computer upstairs.

[RickKrung]

...snip...
Our trig based programs can produce extremely precise answers, far more precise than we require or can measure.
...snip...

I do not disagree that we cannot actually measure to the same precision that we can set the angles, using these programs.  Measuring these angles is not what I think the programs do.  The programs do not provide "answers", they provide "settings".  I value them for the consistency they bring to grinding/deburring from one wheel to the next at the same (or higher) angle.  This keeps the bevel uniform and I believe speeds the sharpening process.  And, following Knife Grinders' procedures for deburring requires precision in setting the honing angles at increments greater than the grinding angle, for many knives.  That to me is where the value is, not knowing or caring about precisely what the angle actually is. 

Just yesterday and today, sharpening one knife for a friend of my daughter's and eight knives for a friend of mine, my CATRA goniometer had died and I don't have a replacement, so I estimated the existing angles by the black marker method.  Then I set angles using the Go Calc app and proceeded to sharpen.  Using the app, I was able to set the angles for each successive stone/wheel, using the distance from the USB to the stone, and keep the bevels nice and clean and uniform.  BTW, I like this method.  Cleaner and easier for me.  And I like the resulting bevels. 

And for the record, I am not commenting at all about the kenjigs.  I have or use any, so I have not basis for commenting on them.  Not a criticism, just a statement for clarity. 

Rick

[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.

[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

[RickKrung]

...snip...
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

[Ken S]

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