I need help with two things.
First, I would like a better term for the process we have been developing to set bevel angles. "Kenjig" is just a tool which uses the trig. (Incidentally, for the newcomers, I originally named it KS-150, meaning Knife Setting, 150mm length, following the Tormek convention. Sweden thought this name might be confused to imply that it was an actual Tormek product, so I had a forum contest for a new name. Any resemblance between KS and my initials was purely coincidental. :) )
"Torig" sounds too much like a British political party. "Trigmek" misses the mark, also. I would like us to coin a word which would indicate the process without scaring away the majority of members and guests who, like me, are somewhat math challenged. (Jan's term "Mr. Euclid" has a nice ring to me.)
The second area where I need help is in expanding the concept to a more general level. I want to include other tools, not just for knives where a 139mm protrusion is convenient.
Looking at the grinding bevel set up as a triangle: one side would be the distance from the top of the universal support to the surface of the grinding wheel. Let's call it D (distance). One side would be the protrusion of the combined jig and blade from the back of the universal support to the grinding wheel. Let's call it P (Protrusion). The third side is actually not a straight line. It is the arc of the grinding wheel as measured from the two points of intersection. Let's call it G (Grinding wheel).
Using our knife set up, the angle formed by P and G is 15°. In Tormekese, this is called the bevel angle. If we increase P or D and keep the bevel angle constant, the increases in the sides should be proportional. As an example, if we have a small carving chisel with a protrusion (P) of 25mm, how would we determine the distance (D)?
I tried unsuccessfully using Dutchman's tables, dividing one side into the other, to determine a factor. Wouldn't it be convenient to multiply P by factor X and calculate D?
If that doesn't work, having a table where the rows represented Distance; the columns represented Bevel Angles; and the intersection numbers represented Protrusion would make set up much more efficient. We would have to factor in grinding wheel diameter changes somehow. Using the TTS-100 or Han-Jig might eliminate the need for multiple tables.
Using the carving chisel as an example, if the Protrusion was set at 25mm by use of a stop block or rule; by using the table, we would match the Protrusion with the desired Bevel Angle and obtain the Distance.
In the ideal, perhaps unrealistically simple world, we would just multiply 25mm by the Distance factor for 15° to get the answer.
We should be able to use this concept with almost any tool. I know where I want to get; I just don't know how to do the math. Any help from the Forum Mathematics Department will be most appreciated.
Thanks.
Ken
Ken, I admire your tireless efforts to generalize and simplify the grinding setup process. :P
The explanation of your unsuccessful application of Dutchmen's tables to define parameters for your carving chisel is simple. Each Tormek jig is to some degree world of its own and has to be considered separately.
It is not possible to expect that a relation between two quantities (e.g. P, D) characterizing Knife jig setting is directly applicable to Square edge jig or some other jig.
From geometrical point of view there are simpler jigs (e.g. Knife jig and Square edge jig) and more complicated jigs e.g. the Gauge jigs. ;)
You are correct expecting that it is possible to calculate tables relating selected setting parameters with stone diameter and desired bevel angle which would make set up more efficient. Each jig will have its own table/tables. :)
Jan
Jan
Thanks for your reply. The project may be more involved than I realize, however, I believe the benefits will justify the effort!
Ken
Quote from: Ken S on June 29, 2016, 01:51:38 PM
Looking at the grinding bevel set up as a triangle: one side would be the distance from the top of the universal support to the surface of the grinding wheel. Let's call it D (distance). One side would be the protrusion of the combined jig and blade from the back of the universal support to the grinding wheel. Let's call it P (Protrusion). The third side is actually not a straight line. It is the arc of the grinding wheel as measured from the two points of intersection. Let's call it G (Grinding wheel).
I would need to see a drawing of this "triangle". I tried to make one, but P and D don't meet to form a corner of the "triangle". Rather, they intersect somewhere inside the Universal Support rod.
Herman, the end result is setting the Distance and Protrusion, either with a gage block or combination square (or similar tool). I would draw the triangle from the point on the universal support where the stock of the square rests to the point on the wheel where the blade rests. Drawing a line across the grinding wheel, as is used with skews, and then lining it up with the knife edge will determine where the Protrusion side is drawn. The Distance line would be from where the square's stock rests on the universal support to the point where the square's blade intersects the grinding wheel.
Ken
Hmmm... I'm having trouble understanding your description, Ken. This is a case where a picture really would be worth a thousand words.
Good point, Herman. I'll work on some photos.
Ken
Herman,
Here is my attempt at posting
Herman,
The first image shows a knife in the jig. The Protrusion is 139mm, as I use with the kenjig.
(http://i1248.photobucket.com/albums/hh491/tormekman/250f13b3-0c07-41a6-ac74-bfa7851ef0a7_zpsbmhajsxk.jpg)
The second image shows a combination square substituted for the knife and jig. (Sorry the rule is not metric; I don't have a metric blade for my square.) This shows what I want the Protrusion side of the triangle to be. The end result is being measured by the combination square or the line on the kenjig.
(http://i1248.photobucket.com/albums/hh491/tormekman/5a2648e1-b567-4da6-9437-4b0f9aed8602_zpsolmkwage.jpg)
The third image shows the combination square being used to measure the Distance. In this case it is 80mm, s per Dutchman's tables. like the Protrusion side, the Distance side of the triangle has an end product of being measured with the combination square or the groove in the kenjig.
(http://i1248.photobucket.com/albums/hh491/tormekman/e225cd75-133c-46f5-844d-e888c792b5de_zpspvnf7cqt.jpg)
These points may not exactly fit orthodox trig, however, they are practical for the use.
Ken
ps to Grepper.......Thanks for your photo bucket help!!!!!!!!
Jan,
I have been thinking about your comment about the differences in the Tormek jigs. I think the jigs which might benefit from this angle approach fall into two groups:
1) Jigs which are used by being attached through the universal support. Probably the only jigs of this type to pursue are the versions of the square edge jig. Protrusion is the total of jig protrusion and tool protrusion. As the jig protrusion remains constant, we can measure just the tool projection. Tormek pursued this path with the gouge jig and TTS-100.
2) Jigs which are pressed against the back of the universal support. In this case, with the notable exception of the knife jigs, jig protrusion is zero and tool protrusion equals Protrusion. The short tool jig, multitool jig and the knife jigs are this type of jig. As the knife jigs are not attached to the universal support, a combination measurement is easily obtained. Case in point is my 139mm figure.
Essentially, the only difference between the two types of jigs for calculation purposes is that the "through jigs" have a two step protrusion and the "to" jigs have only one step.
I grant that these jigs will not cover every tool, however, they do cover most tools commonly used.
Protrusion and Distance can be obtained by using trig tables. They can also be obtained by conventional setting methods (Anglemaster, black marker, etc). Probably the easiest method for most of us would be to make up a simple file card with the tool, jig and grinding wheel used (including coarse or fine with the SG), and the Distance and protrusion measurements. Once recorded, these measurements could either speed up future setups or be the basis for a kenjig for that tool.
Ken
Yes, Ken, I agree with you. :)
Another parameter that distinguishes Tormek jigs is the height of the tool edge above the USB. For the Knife jig it is 6 mm, while for the Square edge jig it is some 25 mm. ;)
(http://img21.rajce.idnes.cz/d2102/11/11771/11771137_37021e568ec44478b9ce7dc74d286378/images/Knife_jig_125_15_hor_OK_rev1_700DPI.jpg?ver=0)
Jan
D'(D'+2R)=P'(P'+2R sin ß)
where D'=D-r
and P'=P-r
and r =6 mm, the radius of the Universal Support rod,
and ß is the bevel angle.
And R is the radius of the grindstone (125 mm for a new one with no wear).
Quote from: Herman Trivilino on June 30, 2016, 05:54:00 PM
D'(D'+2R)=P'(P'+2R sin ß)
where D'=D-r
and P'=P-r
and r =6 mm, the radius of the Universal Support rod,
and ß is the bevel angle.
And R is the radius of the grindstone (125 mm for a new one with no wear).
Herman, thanks for the formula. :)
Please did you check whether your formula gives the same results as the Dutchmen tables? Kenjig uses P=139 mm, D=80 mm, R=125 mm and β=15
o.
Jan
P.S.: Your formula will be in compliance with Dutchman tables only when D'=D. After this correction your formula can be converted to the initial Dutchman's equation F0. This formula is approximate. The approximation concerns the way how we measure the distance D between USB and the grindstone.
Hopefully exact set of Kenjig parameters is following: P=139 mm, D=78,9
67 mm, R=125 mm and β=15
o ;).
Herman,
I have been working with your formula. Some quiet time when the grandchildren are not with us should produce better understanding. I'll keep you posted.
Ken
Quote from: Jan on June 30, 2016, 08:54:20 PM
P.S.: Your formula will be in compliance with Dutchman tables only when D'=D. After this correction your formula can be converted to the initial Dutchman's equation F0. This formula is approximate. The approximation concerns the way how we measure the distance D between USB and the grindstone.
Hopefully exact set of Kenjig parameters is following: P=139 mm, D=78,67 mm, R=125 mm and β=15o ;).
Do you mean the Dutchman tables give approximate figures? Because I'm not aware of any approximations made in the derivation of the formula I posted.
Quote from: Herman Trivilino on July 01, 2016, 06:17:14 PM
Quote from: Jan on June 30, 2016, 08:54:20 PM
P.S.: Your formula will be in compliance with Dutchman tables only when D'=D. After this correction your formula can be converted to the initial Dutchman's equation F0. This formula is approximate. The approximation concerns the way how we measure the distance D between USB and the grindstone.
Hopefully exact set of Kenjig parameters is following: P=139 mm, D=78,67 mm, R=125 mm and β=15o ;).
Do you mean the Dutchman tables give approximate figures? Because I'm not aware of any approximations made in the derivation of the formula I posted.
Good question, Herman, I have to clarify my statement concerning approximation.
Dutchman formula and your formula for D'=D provides the same numerical results. Your formula can easily be converted to Dutchman's formula F0.
The approximation which is used in both is conceptual one. Dutchman and you assume, that D is the distance between the USB and the grindstone surface. This is only approximately true. The real distance D is measured along a line connecting the centre of the universal support rod and the centre of the grind stone. The error introduced by this approximation is less than 2 mm.
(http://img21.rajce.idnes.cz/d2102/11/11771/11771137_37021e568ec44478b9ce7dc74d286378/images/Knife_jig_125_15_hor_OK_rev2_720.jpg?ver=0)
Jan
I go back to the source document of this project. Dutchman's Grinding Angle Adjustment booklet is posted on the forum. Everyone interested in angle adjustment should print it or download it. I have both printed copies and have it in ibooks on my ipad.
Ton's(Dutchman) booklet contains more than tables and formulae. Ton has stated the purpose of this whole project in the introduction. He wanted a simple system which could be realized by measuring and adjusting the position of the universal support and the length of the adjustable jig. His purpose has been my guiding North Star.
I think Ton may have designed his tables to work with a combination square (with a metric blade). I am certain that as he sharpened knives this way, he zeroed in on just a few well chosen combinations.
All I added was a belief that a combination of positioning the universal support and adjusting the jig(s) which would allow single setup which would work for most kitchen knives. The simple jig would also allow rapid and accurate to those settings.
I don't want forum readers to lose sight of Ton's vision, his simple system. I am glad we have several helpful members to make sure this system is accurate as well as simple.
Ken
Quote from: Jan on July 01, 2016, 08:39:53 PM
The approximation which is used in both is conceptual one. Dutchman and you assume, that D is the distance between the USB and the grindstone surface.
I didn't assume that. I was told that it was the definition of D.
Here is the figure I used to derive my formula:
(http://i1291.photobucket.com/albums/b553/htrivilino/Tormek%20Jig_zpshshu6g2d.png) (http://s1291.photobucket.com/user/htrivilino/media/Tormek%20Jig_zpshshu6g2d.png.html)
The large circle is the grindstone of radius R, the small circle is the US rod of radius r.
I simply applied the law of cosines to the triangle shown in the figure, and the trig identity cos (90°+ ß) = - sin ß.
Deleted post made in error.
Quote from: Herman Trivilino on July 01, 2016, 11:41:10 PM
Here is the figure I used to derive my formula:
(http://i1291.photobucket.com/albums/b553/htrivilino/Tormek%20Jig_zpshshu6g2d.png) (http://s1291.photobucket.com/user/htrivilino/media/Tormek%20Jig_zpshshu6g2d.png.html)
The large circle is the grindstone of radius R, the small circle is the US rod of radius r.
I simply applied the law of cosines to the triangle shown in the figure, and the trig identity cos (90°+ ß) = - sin ß.
Quote from: Herman Trivilino on July 02, 2016, 01:59:21 AM
Deleted post made in error.
Thanks Herman for your figure which illustrates your approach. :)
You still stay conceptually approximate, because the angle β in your figure is not exactly the real bevel angle, which we will get as the result of knife sharpening using a Knife jig.
I have added a red line to your figure which shows the longitudinal axis of the Knife jig, which is 12 mm above the centre of the universal support rod. The real knife bevel angle has to be measured with respect to the red line.
(http://img21.rajce.idnes.cz/d2102/11/11771/11771137_37021e568ec44478b9ce7dc74d286378/images/Modified_Herman_720DPI.jpg?ver=0)
The problem is slightly more complex and cannot be solved exactly by one application of the law of cosines. ;)
Jan
Looking at Dutchman's tables, if the 6mm radius of the universal support is critical, moving from the 80mm distance column, which shows a 139mm protrusion to the 75mm distance column which shows a protrusion of 133 mm might help.
My unmathematical gut feeling is that this is an oversimplification.
With the error, if we maintain the same physical (and uncorrected) D and P dimensions, would the only difference be the sin? If so, how much would the error be in degrees of bevel angle?
We have not discussed tolerance. Even Weber gage blocks of laboratory tolerances have a tolerance range. The range may be + or - a couple millionths of an inch or equivalent in microns, however, even these are not "exact".
.2588, the commonly used sine for 15°, is rounded off, as is either 3.14 or 3.1416. We introduce many small errors. Even our grinding wheel radius is an approximation.
I believe we should determine a tolerance range which seems generally acceptable. Plus or minus one degree? two degrees? thirty minutes?
The other tolerance consideration should be the tolerance range of the black marker and Anglemaster. Even when used very skillfully, the black marker is dependent upon the accuracy of the existing bevel angle. Tormek has not shared its projected accuracy tolerance of the Anglemaster, with good reason. A machinist, fully realizing the limitation of even the most precise measuring tools, would not be taken aback by a realistic tolerance range for the Anglemaster, nor should he. The average customer, totally oblivious of measurement limitations, might question the value of a very workable tool.
This is leading to the question of how does the accuracy of our tables and formulae, as used with our various forum jigs compare with the traditional Tormek methods? We should be aware of both accuracy and efficiency. The other question is how accurate do we need or want to be?
Ken
Ken, we are not discussing here some negligibly small changes in bevel angles. The consequence of a non-justified simplification or unconscious approximation can be that we sharpen a bevel angle of 12o instead of the desired 15o.
The great importance of the Dutchman approach is that he selected suitable geometrical approximation which lead him to relatively simple calculations with acceptable accuracy. :)
Wootz slightly modified Dutchman's approach. He sets the height of the USB above the Tormek housing. This approach works even more precisely than the Duchman's. :)
On the other hand, Herman suggested an approach, where the distance D is perfectly defined, but the bevel angle is biased. His corrected formula is trigonometrically correct but the approach is not suitable for prediction of the bevel angle with acceptable accuracy. ;)
The point is to find simple expression which gives predictions with acceptable accuracy, e.g. 0.5 mm in distance measurements and less than 0.5o in bevel angle.
Jan
Jan, please understand that I am not criticizing. I make these post questions in order to learn and understand. I believe in this concept of setting bevel angles. I also believe that the fine math work done here will help support a solid concept with very precise control.
I did not have a concept that the combined error might be three degrees. That does need work. I find the tolerance range you put forth of .5 mm in length and .5° quite adequate.
I see the end result as a very easy to follow procedure, well within the grasp of our members, yet supported with very solid trig. Originally I thought this process would benefit new users, users who sharpen infrequently, and very busy, high production sharpeners who must sharpen a variety of knives and tools. I still believe it serves all three groups and is a significant step forward.
I do appreciate the combined expertise.
Ken
Ken, I am not afraid you are criticising the lengthy discussion here. I know you are expecting the outcome which you will integrate into you considerations. Detailed understanding how the knife sharpening works is for us Tormekers crucial. :)
I do not need to convince anyone, but when the discussion is open and it is about conceptual questions I can be pretty insistent.
In comparison with the geometrical concept of the TTS-100 setter the knife sharpening geometry is an easier issue. ;)
Jan
I have deleted the contents of Reply #19 because I had not made the error I thought I'd made! Unfortunately Jan has quoted that material in Reply #20.
For clarity, let me state that the correct relations are the ones I originally stated:
D'=D-r
P'=P-r
Herman, if you wish I can delete my quote of your reply #19 also. Let me know. :)
To understand you correctly, your formula is now given in reply #11 and the figure in your reply #18 was used to derive it.
My major objection is expressed in reply #20. Your quantity β is by some 5o smaller than the real edge angle! :-\
Jan
Jan, yes what you say is correct. I had not accounted for the bevel angle ß properly. I will have to go back to the drawing board.
OK Herman, please take your time, we are not in a hurry. :)
It is really an essential issue for knife sharpeners.
Jan
Jan,
In English, we have an epression "a twofer". "Twofer" is a corrupted spelling of "two for", and means an unexpected second item at no extra cost. In a store, if one purchases one item and gets a second item at no extra cost, one gets a twofer.
For me, this process is a twofer. I began working on this process very shortly after purchasing my Tormek in 2009. This was long before Dutchman posted his tables or the kenjig. My original motivation was to discover a more efficient way to set up chisels and plane blades. I have always marveled at the combination of the TTS-100 setting gage and the SVD-185 (now SVD-186) gouge jig. The combination seems so logical and automated for turning tools. I wanted to achieve that same degree of automation with chisels and plane blades. I used the A and B settings on the TTS-100 as consistent Distance settings. I placed a blank piece of label maker tape in one of the protrusion slots and marked protrusion distances for different bevel angles with a black marker.
These Protrusion settings were established by setting Distance and adjusting the blade protrusion until the Anglemaster indicated the setting was correct. It was very low tech, but quite repeatable and consistent. I was looking for consistency and repeatability, as I had no reservations about the accuracy of either the Anglemaster of the marker method.
I still have no reservations about the accuracy of the Anglemaster or black marker. Many thousands of edges have been happily sharpened with these methods.
For many years I have had a fascination with machine shop tools and measurement. One of the century long standaards for precision measurement is using a set of "Jo Blocks". "Jo Blocks" is the machine shop floor term for Johansson Blocks, named after Carl Edvard Johansson, the Swedish machinist who invented them in 1896. These deceivingly simple metal blocks are capable of quite precision measurement to .001mm or .0001". (Look in wickipedia under "gauge blocks" for more information.)
The kenjig functions as a less precise gage block, as do the protrusion stops on the TTS-100. Being able to incorporate some of the accuracy of gage blocks is the unexpected twofer of the project for me. I recognized this when I first read Dutchman's booklet posted on the forum. While I do not have the mathematical skill to produce the work myself, I am aware enough to recognize the potential of incorporating math into the project to introduce much more precise results. We have the very good fortune on this forum of having members with the math skills to produce this work without introducing substantial cost into making the jigs. In industry, going from an accuracy of .0254mm (or .001") to to .00254mm (or .0001") would involve substantial cost. We can tighten tolerances to a practical maximum with essentially no extra cost. That is much added value.
I find this project increasingly exciting. I do not expect it to work with every blade in the shop. I believe that would be carrying a good idea to the point where it did not work well. I do believe it has the potential to make Tormek sharpening easier and more efficient.
Ken
Thanks Ken, you have taught me a new word "a twofer". I think a similar idiom in my language may be "to kill two flies with one slap". :)
In my opinion a detailed understanding how a jig works geometrically is a prerequisite for musing about its combination with the TTS-100.
In this topic you can hopefully learn something new about the Knife jig which is a necessary condition for understanding how it can be set using the modified TTS-100. To understand how the TTS-100 works is a separate issue.
My accent is always on concept because the actual trigonometrical calculations are only an exercise of secondary school math. It is a craft that is not particularly complicated and can be executed by your children or grandchildren if you've already forgotten it. :)
In some instances of course it is highly desirable when everything can be accomplished in one mind. I'm thinking about this beautiful but geometrically complicated jig. ;)
(http://img21.rajce.idnes.cz/d2102/11/11771/11771137_37021e568ec44478b9ce7dc74d286378/images/SVD_186_739DPI.jpg?ver=0)
Jan
Jan,
I enjoy your critical thinking; your thoughts help me focus.
I realize some of my earlier thoughts were naive. There is no magic bullet where we can multiply a measurement by X and get the universal right number. I do not think that this discounts the whole process. Let us put together a hypothetical example:
We may have one hundred edges to sharpen. (for easy percentages) Fifty are knives; twenty are chisels; ten are plane blades; twenty are misc. woodworking, carving and turning tools. Of the fifty knives, perhaps thirty five fit easily in the Tormek knife jigs and kenjig. Of the fifteen remaining knives, half are too small, some are too thick or not shaped well for the jigs, and one is a machete.
Of our hundred edges to be sharpened, half to two thirds may be readily sharpened using either the kenjig or the TTS-100 and stop blocks. The remaining edges are more practically set up using the Anglemaster or marker with trial and error. Of this group, perhaps a majority could be easily set for future resharpenings by making careful measurements and notes.
The initial sharpening will involve the full set up time for the latter group of edges. The first samples of the first group may involve minor set up time. Let us make a wild guess that the total set up time is reduced by half using math and tools like the kenjig, Han-Jig, TTS-100, and stop blocks.
The second and following sharpenings will be even more efficient. Not only will the job be completed in less time, the results will be more consistent. We must recognize the reality that not all edges or jigs will fall into this happy category. Hopefully the number which require more than a carefully noted initial sharpening will be small.
I do not seek perfection, merely substantial improvement based on both math and simple jigs.
Ken
Yes Ken, I agree with you. :)
For me it is very important to have an alternative way how to set an edge angle. You have mentioned Kenjig and Han-Jig (based on TTS-100 setter modified for knifes).
I would like to add my bi-directional horizontal platform and my modified Starrett square http://forum.tormek.com/index.php?topic=2879.msg15575#msg15575
in combination with the Excel spread sheet for calculating the wheel-support distance. https://www.dropbox.com/s/ypbtaxgycgoyls0/KENJIG_wheel_support_distance_1.xlsb?dl=1
With such portfolio I am sure it is possible to set the edge angle for almost every knife. ;)
Jan
Quote from: Ken S on June 29, 2016, 01:51:38 PM
I need help with two things.
Looking at the grinding bevel set up as a triangle: one side would be the distance from the top of the universal support to the surface of the grinding wheel. Let's call it D (distance). One side would be the protrusion of the combined jig and blade from the back of the universal support to the grinding wheel. Let's call it P (Protrusion). The third side is actually not a straight line. It is the arc of the grinding wheel as measured from the two points of intersection. Let's call it G (Grinding wheel).
Using our knife set up, the angle formed by P and G is 15°. In Tormekese, this is called the bevel angle. If we increase P or D and keep the bevel angle constant, the increases in the sides should be proportional. As an example, if we have a small carving chisel with a protrusion (P) of 25mm, how would we determine the distance (D)?
I tried unsuccessfully using Dutchman's tables, dividing one side into the other, to determine a factor. Wouldn't it be convenient to multiply P by factor X and calculate D?
Ken
Ken, I went back to your thoughts concerning proportionality between protrusion P and distance D when the bevel angle should remain constant.
If we consider one particular jig, e.g. the knife jig, then such coefficients of proportionality can really be found.
For example consider your kenjig for parameters P=139 mm, D=79 mm and bevel angle 15
o. Stone radius R=125 mm. When you have a smaller knife with protrusion P=134 mm you will have to set D=75 mm to keep the bevel angle 15
o. This means that some 80% of the decrease in protrusion is equal to the decrease in distance D between the USB and the grindstone. I hope this was your point. :)
Jan
Thank you, Jan. That is just what I am looking for!
If I understand you correctly,
Distance new = Distance old - [(Protrusion old - Protrusion new) x .8]
D2 = D1 - [(P1-P2) x.8]
Is this correct?
Ken
Yes, Ken, your formula is correct. Congrats! Your intuition was right. :)
The factor 0.8 was stated as a rule of thumb. For grindstone with diameter 250 mm the factor is 0.84 and for grindstone with diameter 200 mm the factor is 0.88.
Please keep in mind that this factor it is valid only for the knife jig.
Please be so kind and test it experimentally. I have derived it as desktop exercise. ;)
Jan
Jan,
Your patient math logic has helped me see that there is no magic X to interject in all Tormek math. If these equations help us set up quickly back and forth with different knives within acceptable or better tolerances, that is a good step forward.
I did not mean to overlook your adapted combination square tool. The English idiom "a senior moment" fits. Incidentally, I just acquired 150 and 300 mm blades for my combination squares. Less chance of conversion errors.
Ken
Ken, you are welcome! :)
Please keep in mind that even with the more accurate figure for the proportionality factor the formula remains a rule of thumb. It means it is not strictly accurate and reliable for every situation. It is an easily applicable procedure for correcting the stone – USB distance when the protrusion is not equal to 139 mm.
When you need exact figures you can use my Excel spread sheet for calculating the wheel-support distance. https://www.dropbox.com/s/ypbtaxgycgoyls0/KENJIG_wheel_support_distance_1.xlsb?dl=1
An adapted combination square tool is very good for various settings experiments which are beyond the kenjig range, e.g. protrusion 190 mm for cleaver sharpening requires wheel-support distance 123 mm for 15o bevel angle.
http://forum.tormek.com/index.php?topic=2879.msg15569#msg15569
Both the 12 mm Al sleeve and the Al contact block can be made of hard wood or suitable plastic also.
Jan
Jan,
When I was much younger, I was a student and then an Assistant Watch Officer at the Hurricane Island Outward Bound School in Maine. A major part of the twenty six day program involved being in in thirty foot (7 meter) pulling boats for several days at a time. These were similar to lifeboats or the small boats used by whaling vessels. To measure the speed of the boat, we would drop a chip of wood next to the bow of the boat and count the seconds needed for it to pass the stern. Our friend, Mr. Euclid, would not have been impressed with the accuracy of this method, however, it was adequate for our purpose.
Our "rule of thumb" knife bevel figures strike me as also being adequate for most of our purposes. It is comforting to have more precise tools available for more critical work. We can also strive to tighten the tolerances of the rules of thumb.
Incidentally, the machinist Leroy Starrett hired to make his original combination squares thought the idea was worthless. Fortunately, Starrett was determined and today we are still using his very useful tool.
Ken
Ken, in this country we use similar procedure to calculate how far away is a thunderstorm centre from us. We count the seconds needed to hear the thunder after the lightning flashed through the sky. Then we divide the number of seconds by three and say that the thunder struck so many kilometres away from us. :)
For you living with imperial units this rule of thumb should be modified to miles. You would have to divide the number of seconds by five and say that the thunder struck so many miles away.
The reasoning behind this rule of thumb is that sound needs three seconds to travel a distance of 1 km or 5 seconds to travel the distance of 1 mile. ;)
Jan
Ken,
in my previous post I have issued a warning that each Tormek jig is a world of its own. Nevertheless the knife jig and the square edge jig belong in my thinking to the same category, those two jigs differ in edge height above the USB. (The height is measured when the tool axis is horizontal.)
I have preliminarily addressed the question whether the proportionality factor concept will work also for the Square edge jig and to my large surprise the answer was positive. ::)
If you have a grindstone with 250 mm diameter and a tool protruding 50 mm from square edge jig than you have to set the stone - USB distance 32 mm for the edge angle 25o. In this case the proportionality factor is again 0.84.
An average value of the proportionality factor X for protrusions between 50 and 75 mm is 0.86.
In the case of the square edge jig the rule of thumb is less accurate than in the knife jig case, but in principle works also. ;)
Jan