How dgriff explained it is pretty much how I approached the Rajah III. However, even after using the pre-wrap to fill in the voids created by the taper, I was not able to achieve a perfect right / left side matching reading. Mainly because the bevels were not exactly the same from the factory. Readings were close enough that I was able to work with it. For smaller blades (like for the Spiderco Dragonfly 2 I sharpened today), this method was not very practical. Since the bevels were pretty even, I just adjusted it in the vise with pre-wrap until I got matching readings. In my mind, that would indicate that it was perpendicular (edge -spine) to the base.

I've come to the conclusion that many blades from the factory, especially thick, like say an ESEE-6, the grind is not even on the blade body .. side to side.
I had one in particular that drove me mad and assumed that was the only explanation.

My post was done at work, so it was kind of a mental exercise. Soon as I got home, I found an easier way to get the angle. Zero the cube on the base, then lay the FFG blade down so it is flat against the base (the handle will necessarily hang off the edge). Put cube on blade and measure angle. IF the grinds are symetrical, the angle of each side is the measured angle divided by 2. My Spydie super steel was about 5.2°, so about 2.5° per side.


Yes, for smaller blades, using the cube will be a problem. However, the human eye can do some amazing things. One of them is to find the center of a circle. The other is to see motion of the smallest amount out of the corner of the eye (watching out for Mr. Sabertooth...), and seeing that lines are askew, or not parallel (your picture frame and the ceiling/wall junction).
One should be able to, if you take your time, place the knife in the vise and see the symmetry in the gaps between blade and jaw. One should be able to look from behind down the edge and see that it is or is not canted to one side.
Just my additional thoughts.

dgriff wrote:


Don
You have a keen and astute mind. You must be either a scientist/philosopher of some bent or perhaps a highly skilled machinist/technician. Whatever you do for a living you have a way of thinking with great clarity and then being able to pass on your thoughts for others to follow. Glad you are here mate!

Leo