Originally Posted by
Marshal
I don't think the issue is that the DMT isn't as flat as we think it is. One of my friends is an auto body tech. He saw me flattening stones with a figure 8, and pointed out that doing that would still allow stone particulate to focus near the center and it would never be perfectly flat. I can't recall what technique he told me to use, I was too entrenched in lapping the stone and just wanted it done. And the DMT gets the stone flatter that sand paper, and more than flat enough to hone a blade...
Now, look at your Shapton plate. See all those low spots that not only relive that suction effect but give swarf a place to accumulate that won't effect the plates cutting action - especially if the plate is on bottom and the stone riding atop it?
I would wager the Shapton is indeed getting your stone slightly more flat. But how flat does a razor stone need to be to get a razor sharp enough to shave? My face doesn't know the difference between the edge put on a blade by my still slightly convex Arkansas hone, which was lapped with a glass plate and loose grit SIC, and the dead flat one that came from Dan's and just got burnished. YMMV.