Jan's graph says a lot. When I designed the kenjig, I decided to leave the Projection constant (at 139mm, although the 140mm used by others is just as valid). I wanted to incorporate the self correcting double wheels of the TTS-100. Although Tormek only uses this patented feature for turning tools, it can just as easily be used for woodworking tools and knives.

Jan's graph, like Dutchman's tables, uses diameter changes of ten millimeters. I constructed the kenjig using the 15° line on Dutchman's 250mm diameter chart. Going across to 139mm Projection, I went up to 80mm Distance. At first I debated between making a set of kenjigs for ten millimeter diameter wear reduction or dedicating the kenjig to that particular grinding wheel and modifying the jig as needed for wear. Kenjigs cost almost nothing to make, and they are quickly made. Either option would work. A professional sharpener might prefer to make a set.

At the risk of sounding like a heretic, I do not believe that home shop sharpeners, the majority of us, need to be concerned about wheel wear. Wheel wear of ten millimeters (diameter) will change the bevel angle by about one degree. (2° with the double bevel). I can see where that amount of change might make some of us nervous. If so, it's time for a new kenjig. I make the wooden kenjigs using my table saw and bandsaw. The set up is what takes the time. I think it is wise to make up several spare blanks. With a diameter change of one millimeter, a change of 1/10° will happen. Yes, this is noticeable with the math. Can we accurately measure this change, or, more importantly, can we detect a difference in cutting?

How long will it take the average home sharpener to wear off ten millimeters from his wheel diameter? How many longtime Tormek users are still using their original grinding wheels. For most of us, wheel wear is glacial.

As constant diameter diamond and CBN wheels become more commonly used, I see wheel wear becoming increasingly less important.

Several years ago, I was particularly impressed with the comment Jan made pointing out the error in my kenjig. Jan is enough of a highly skilled mathematician to notice the error and a practical and honest enough sharpener to also note that the error was not significant.

We need both skilled mathematicians and practical sharpeners.

Ken