Thread: How flat is flat for a hone

Originally Posted by Glock27

Enigmatic!
Some time back I purchased a Chinese Hone rated as 15,000 grit. I had not used it, and happily so, when I discovered that one should check the flatness of their hones. Fortunately for me I possessed an engineers straight edge (used it to assure the flatness of an engine block and head for a proper fit). I laid the straight edge down on the Chinese hone--parallel to the long edge of the stone and noted that either end displayed light indicating that the central part of the stone was not flat, but rather convex. I contemplated the purchase of a flattening hone but opted for my table belt sander. With the straight edge, and patients, I finally achieve what I believe to be a perfectly flat "Chinese" 15,000 grit stone. The opposite side was the opposite. The edges were high creating a bowl like center. The process of eliminating the bowl center took as much caution and patients as the opposite side but with time and patients the bowl was eliminated and I created a hone "engineer level" flat.
The ease with which the stone was removed makes me wonder if the hone is truly a 15,000 grit. Since the stone was inexpensive the belt sander worked fine despite the finish using a 400 grit sand paper on a flat granite surface.
Anyone ever have the occasion to flatten a hone? How did you do it? How long did it take? What are your suggestions?

I used in the beginning the Norton flattening stone. I then progressed to what I use now which is the DMT lapping plate. It is way more precise and works great. Every so often I simply use a pencil to make cross marks across the hone both vertical and horizontal. I then place under water and start to lap the hone. I stop every so often to see where the stone still has pencil marks and know that is a area that is lower than the area that is now missing the pencil marks. I continue until all marks are gone. I then do again and do a few strokes and if they all are removed simultaneously I know it is lapped to a degree that will yield great results.

There will be others to chime in on their method as well. Good luck.