What does lapping a stone mean? How do you go about doing it? When do you need to lap a stone?

jmsbcknr
Lets use the example of a Norton 4000/8000 stone. Lets suppose that the 4000 side is slightly dished in the center and as a result your razor is not making contact with the stone at that area.
You need to "lap" (flatten) the stone.

The procedure:
1. Find a flat surface such as a countertop, top of a table saw, piece of ploished marble or granite
glass shelving piece,etc. , you get the picture.

2. Place a sheet of wet/dry 320 grit sandpaper on the top of ther flat surface. Make sure to wet the sandpaper on both sides. This will cause the sandpaper to "stick" to the flat surface.

3. Now place the 4000 side of the stone down on the sandpaper. Using an X pattern perform 10 laps in each leg of the X. Turn the stone over and examine the surface of the stone. You might see a small difference in color and texture where there is a dished spot.
Turn the stone back over and place it on the sandpaper again and perform 25 more laps with the X pattern. Examine again. Repeat as necessary.

4. When there is no difference in the color and texture on the hone then you are done.

Hope this helps,