WHY 139mm?

[Ken S]

Some of you may wonder why several of us have chosen to standardize on 139mm Projection. EDIT: In the original post, I neglected to state that forum member, Dutchman(Ton Nillesen) explained this in his grinding Angle Adjustment booklet in 2013. The error of omission is mine. Dutchman's work is the basis for all of the recent angle development. I have referenced Dutchman's work so frequently over the years. The omission was a mental slip and not intentional.  Projection is defined as the distance between the edge of the knife and where the adjustable stop of the knife jigs meets the support bar.

What limits this range is the length of the threaded part of the shaft on the knife jigs. 139 mm (Wootz uses 140 mm, which is essentially the same) works out to be a usable mid point when chef's knives and slicing knives are in the jig.
Narrow knives, like paring knives, can use this same 139mm Projection when the SVM-00 is used with the SVM-45. This makes it possible to use the same 139mm Projection and Distance with almost all kitchen knives, almost eliminating the necessity of individual set up time.

Set up combination can be determined with any of the various computer programs or, less efficiently, with trial and error. With grinding wheels which gradually wear down, the 139mm Projection can remain constant and the initial setup for the Distance adjusted when needed. This would certainly not be needed in the middle of a sharpening session and probably not for several sessions.

By standardizing the Projection at 139mm, one of the variables in knife sharpening set up becomes a constant, thus simplifying things.

Ken

[Hannsi1957]

or you can make it easy for yourself by using a laser line and clamping your knife on the stone by aligning it with the laser line and then clamping it. this way you can clamp any knife without measuring and always have your predefined angle.

Hanns

[Ken S]

Yes, Hanns, I could do that. However, by using three pre set knife jigs, I rarely have to do any adjusting or measuring.

I have no doubt that your laser idea is fast and accurate. It probably equals my method, however, this old dog has used my method for enough years to become quite comfortable with it.

Ken

[Hannsi1957]

as always Ken
everyone should do that what he likes most.
like the old saying, never change a running system

Hanns

[Ken S]

Agreed.....

[cbwx34]

or you can make it easy for yourself by using a laser line and clamping your knife on the stone by aligning it with the laser line and then clamping it. this way you can clamp any knife without measuring and always have your predefined angle.

Hanns

You're still measuring... you're just measuring to a laser line. 

In fact, (and correct me if I'm wrong)... you have to first measure a knife in the clamp to the distance you want... so you know where to set the laser, right?

Not easier... just different.

[Hannsi1957]

U right.... I mean u save a lot of time with my method to messure only the first knife and all the next clamp on the laserline. But this is also only possible if u have same wheeldiameter like u have with diamond or CBN Wheels. Then u can switch the wheels like u want with always the same adjustment

Hanns

[Dutchman]

Some of you may wonder why several of us have chosen to standardize on 139mm Projection. I don't believe the simple answer has ever been explained. Projection is defined as the distance between the edge of the knife and where the adjustable stop of the knife jigs meets the support bar.

What limits this range is the length of the threaded part of the shaft on the knife jigs. 139 mm (Wootz uses 140 mm, which is essentially the same) works out to be a usable mid point when chef's knives and slicing knives are in the jig.
...snip

Actually, imho, the 139mm comes from a calculation in my original document.
It is based on the control range of the adjustable stop and a cooks knife with a width of 45mm.
Quotes:

• Length between stop and clamp edge is adjustable from 108 to 125 mm

and:

...
    • The table cell in the column of a given S, in the row of the desired ∆ gives the value at which the adjustable stop of the knife-jig should be adjusted.
Example:
Consider a cooks knife with a width of 45mm. The jig can grip the knife to a depth of 14mm. As a consequence the knife edge extends 31mm from the clamp.
Thus the distance A between the knife edge and the adjustable stop can be varied between 108+31 and 125+31 mm, that is from 139mm to 156mm.

So with a maximum blade width of 45mm, the minimum projection is 139mm.

[Ken S]

Mea culpa, Dutchman.

Please note the edit of my original post. Your Grinding Angle Adjustment work has always been the foundation for the forum grinding angle setting tools and programs. The omission of referencing your work was an oversight on my part. I hope you know it was not intentional. Your work and the handbook are the most referenced works in the "Recent" tab of the books program on my ipad. When I clicked on your work this morning, it opened to the first table, the page after your 139mm explanation. I refer to your tables so frequently that I sometimes overlook your explanation.

Please accept my apology.

Ken

[cbwx34]

Perhaps Simple adjustment of the grinding angle is another thread that should be "pinned", at the top of the "Knife Sharpening" section?

Few threads have 'stood the test of time' and it is referenced often.