a cleaver math question for Jan

[Ken S]

Jan graciously offered to share his math skills to help design a kenjig for cleavers, specifically my Chinese cleaver. So:

Instead of the 139mm standard I adopted with my regular kitchen knives, I would like to use 190mm for my cleaver. That is the distance from the edge of my Chinese cleaver in the Tormek large knife jig with the stop threaded in the middle. By using the middle of the range, we have twelve mm adjustment in either direction. (This would allow cleavers of other sizes to be used.)

My grinding wheel is presently 240mm in diameter. I think a chart from 250mm to 180mm by ten millimeter steps would be useful. (That allows use of the T4 as well.) I would like a chart for fifteen degrees half angle as my primary chart. Those using cleavers for heavier, more carnivorous tasks might prefer twenty degree half angles.

I like the simple wooden kenjig. I dedicate a kenjig to each grinding stone. As the stone wears, I lengthen the groove for every ten millimeters less wheel diameter. Lengthening is only two saw cuts, and takes less than a minute.

With this simple kenjig, I can quickly and repeatably set up to sharpen my cleaver using Robin's Extended Universal Support Bar. I have no need for a threaded micro adjust, anglemaster, or black marker.

I decided to make this a forum topic instead of a PM because I hope it will benefit other forum members. Thanks in advance, Jan. Your math and design skills are much appreciated.

Ken

[Jan]

OK Ken, I will prepare a table of dimensions for your kenjig for cleavers.

Jan

[Ken S]

Thanks, Jan.

I think it will prove useful.

Ken

[Jan]

In the two tables below there are  wheel – support distances (S') for kenjig for cleavers. Both tables are for the projection length 190 mm (Chinese cleaver in the knife jig or the long knife jig).

The first table is for a bevel angle 15^o (edge angle 30^o).
The second table is for a bevel angle 20^o (edge angle 40^o).
Each column corresponds to a specific radius of the wheel.

So, for Ken's stone radius 120 mm and the bevel angle 15^o the wheel – support distance is 125 mm.

Jan

[Ken S]

Excellent work, Jan. Your charts are exactly what I wanted. The charts take away the trial and error part for the new and infrequent knife sharpener. They also allow very efficient and accurate use of the knife jigs with cleavers using Robin's Exrended Universal support Bar.

thanks.

Ken

[Ken S]

I made up a quick kenjig this afternoon. I hope to sharpen my Chinese cleaver tomorrow. The kenjig is compatable with many jig styles, from primitive to fancy. This one favors primitive, but with full accuracy. It is a two inch wide strip of cardboard cut from a piece originally 8 1/2" x 11". Using one short side as a reference point, I drew a pencil line 190mm from that end (the projection distance). I cut out a groove 12mm thick from the reference side 125mm long, following Jan's table for my grinding wheel.

That 's all there is to it. I will probably replace the cardboard with one made of baltic birch plywood someday. Until then my simple cardboard tool will suffice.

Ken

[Jan]

Ken, it may be good to mention, that the kenjig for cleavers will work not only using Robin's extended universal support bar, but also using Wootz "Homemade honing jig & cleaver support"
http://forum.tormek.com/index.php?topic=2583.msg13643#msg13643
or my "Long knives & cleavers jig" http://forum.tormek.com/index.php?topic=2635.0

It can be used to set the bevel angle for grinding away from the edge but also towards the edge. 

Kenjig for the radius 110 mm can be used for setting the honing wheel-support distance for T7. I have suggested to combine the jig for the grindstone and the jig for the honing wheel into double ended kenjig.
http://forum.tormek.com/index.php?topic=2654.0


Jan

P.S.: Caveat: To get the same bevel width on both sides of the cleaver the spine thickness of the blade should not be significantly thicker than 3 mm. Using Wootz modification of the knife jig this figure increases to 5 mm. http://forum.tormek.com/index.php?topic=2577.0

[Ken S]

Jan,

Your point is very taken. The kenjig concept will most certainly work with any of the forum accessories you have mentioned. All are clever, useful tools. They all extend the range of the niversal support bar. For most of us, the primary advantage of Robin's design is that it is available ready made. We could all take a design to a local machine shop and have a tool made. Some of us could and have already done it at home. Robin has done the design work and had the machining done and offers the product at a reasonable price.

I think of the kenjig more as a concept than as a unique tool. In fact, the kenjig name was not my idea originally. It is a combination of two already established setting ideas, the spacer block for the universal support to grinding wheel distance and a stop block for setting the edge projection length. I altered the spacer block to a groove and combined both functions onto one tool. I also found a common projection length so that set up would be identical with various kinds of commonly used kitchen knives. My goal was simplicity for beginners and efficiency for professionals.

The concept should work with almost all edge tools. It began with chisels and plane irons. It should work, as noted by Jan, with any of our tool designs. Jan's double ended idea is a fine example of the power of this forum to improve ideas.

Ken

[Jan]

The drawing shows the geometry of the kenjig for cleavers concept.



Jan

[SharpenADullWitt]

We are now in March 3rd.  Ken how were your results?

[Jan]

When I have realized how quickly the number of kenjig's with different lengths is growing, I have decided to carry out the settings using one simple marking gauge instead of cutting new and new wooden kenjigs. I bought an inexpensive 300mm Combination Square, similar to the one shown below.



I have yet to devise a contact block between the end of the steel ruler and the grindstone. With this simple tool I hope to be prepared for all possible future kenjig lengths. 

Jan

[Elden]

Very good, Jan. It is extremely difficult to find metric measuring tools over here. Most tapes have both scales on them if they have metric, causing them to be almost worthless. EBay does have a few offerings that can become pricey.

[Ken S]

Jan,

Excellent drawing. It is both technically very well done and exactly slows the concept.

SADW,

Good point. I apologize for my very slow limited shop schedule. I hope to find some sharpening time today and will report the results.

Jan,

You have found one of my most used tools, the combination square. I call it a "Starrett square" after the inventor, L S Starrett.You obviously fully comprehend the kenjig concept. I believe Dutchman, who first posted the tables I used, used a Starrett square instead of wooden blocks. The purpose of the jig is to reduce the possibility of measurement errors. This becomes less of an issue with a skilled craftsman. I have a hobby collection of machinist tools. Starrett squares are always "at the ready".

Elden,

Our country has a funny love-hate relationship with metric measurement. I think the most annoying part is when a single item has both imperial and metris components. (The Tormek TS-740 Work Station, which is actually made in Germany, has 5/8" x 11tpi threads.I suspect there is an interesting story behind this!)

The Tormek is really a metric tool.

I agree with your dislike for  combination scales. I can work with either unit; I just don't like looking at them together. Northeastern Ohio, where I lived until I retired, had a very good selection of nice used machinist tools at yard sales and second hand stores. Lots of nice Starrett, Brown and Sharpe and Lufkin tools reasonably priced. Unfortunately very few metric tools. I do not have a metric blade for a Starrett square. I just use the square like a marking gage and measure the blade projection with a 150 mm rule (the metric version of our very handy six inch rule).

Lee Valley sells two sizes of very well made folding rules. The larger size folds out to two meters. It is all metric and has a depth gage section. The smaller size folds out to one meter. It is metric on one size and inch on the other. Both are remarkably inexpensive, quality , useful tools.

Ken

[Ken S]

SADW,

I finally tried Robin's Extended Universal Support Bar with my Chinese cleaver and kenjig with Jan's calculations. Setup was a breeze. The extended usb fit perfectly with the kenjig. No trial and error or micro adjusting. I used the SB-250 in horizontal position (Steve Bottorff's preferred technique.). Only one pass was necessary; my knife was merely dull. For a busy farmers' market sharpener, the larger support bar adjusts quickly for regular kitchen knives. Just use the regular I am pleased with Robin's larger support bar. My Chinese cleaver is now razor sharp again with pristine bevels.

Ken

[Jan]

The two images below, show how I have modified the "Starrett square" for easy setting of the support – grindstone distance in the frame of the kenjig concept. The 12 mm Al sleeve is attached to the body of the square. The sleeve offsets the position of the universal support with respect to the zero on the ruler. This offset is compensated by the contact block made of two Al plates of trapezoidal shape. In this way the proper function of the ruler is preserved. 





The contact block is aligned so, that the centre of its front part meets the grindstone.

Jan

P.S.: I will keep using my wooden double-ended kenjigs for knives. This new tool is intended rather for non-common settings and emerging longer kenjigs.