On Tue, 20 Mar 2018 12:25:58 -0400, Frank Krygowski
wrote:

After trying many techniques over the decades, my favorite tool for
sharpening knives is a steel block whose top surface is impregnated with
industrial diamond abrasive. It seems to last forever, which for
practical purposes means it stays flat.

If it's this type, that has the diamonds imbedded in a sheet of
plastic, they are probably NOT flat.
https://www.harborfreight.com/3-piece-2-inch-x-6-inch-diamond-hone-blocks-36799.html
If it's a far more expensive diamond plate with mono crystalline
diamonds and where the diamonds are embedded in a more stable
substrate, they work very well:
https://www.dmtsharp.com/sharpeners/bench-stones/dia-sharp/
The problem is that the grain size of the diamonds is rather small. In
order for them to remain in place, about two thirds of the diameter
needs to be imbedded in the plastic, aluminum, or whatever. That
leaves very little sticking out to do the cutting. If the substrate
is bent a little less than the height of the diamonds, you'll be
sharpening on air, not diamonds.

This video covers the problems quite well:
"WATCH THIS before you buy diamond stones for tool/knife sharpening"
https://www.youtube.com/watch?v=zBND6emsSE4

I have other whetstones that
have gradually gotten concave, which makes it tough to maintain the
proper edge angles.

Stones are easy to flatten. Take a soft pencil and mark a grid on the
stone surface. Find another stone with a rougher grit and rub the two
surfaces together. The pencil markings will disappear as you grind
from the high spots. Keep grinding until all of the penciled grid
disappears simultaneously.

I use the classic technique, which is sharpen the main bevel at
something like 20 degrees, then lightly sharpen a smaller bevel at 45
degrees, and touch up or polish the edge with a hone or other piece of
hard steel.

I use 15 to 20 degrees for kitchen knives depending on blade
thickness. Mostly, I try to duplicate the original angle from the
manufacturer. I haven't tried any compound angle grinds yet.
http://blissknifeworks.com/wp-content/uploads/2016/10/Grind-Angle-Chart-copy.jpg

I use the hone far more often than the abrasive. Lots of
times, the edge just needs touching up, not actual grinding.

I look at the edge with a magnifier or microscope to see what I'm
dealing with. If it's dings, gouges, or chips, I use the belt sander
to remove these before sharpening. If it's just a little rough, then
I use a finer stone.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558