The Shapton NAORU Cast Iron Lapping System is a great tool for restoring the flatness capabilities of your sharpening stones. Its surface is covered with grooves laid out in a geometrical pattern to increase the synergy between the plate and the lapping powders supplied with it, improving the speed and accuracy when flattening any irregularities on a sharpening stone.

Shapton has a nice description of how to use the system here: https://shapton.co.jp/en/naoru/

The NAORU lapping system allows you to choose the appropriate lapping powder, whether it is coarse, medium, or fine (sold separately), based on the grit of the stone you want to flatten. This ensures optimal results and extends the life of your sharpening stones.

• Dimensions: 250 x 101 x 28 mm
• Weight: approx. 2,600g

The quality of the finish you obtain on the sharpening stone surface will vary depending on the type of powder used, so it is important to choose the right powder for the particular stone you will be lapping. Here are the recommendations:

• For sharpening stones of 40 microns or above (#320 or below), use coarse powder.
• For stones of 4 to 30 microns (#500 to #3000), you can use coarse powder initially if the stone is quite uneven, to scrape it roughly, but then use medium powder to re-lap it. Normally only medium powder is needed.
• For stones of less than 4 microns (#4000 and above), you can use medium powder initially if the stone is quite uneven, to scrape it, but then use fine powder to re-lap it. Normally only fine powder is needed.

It is important to wash the plate and sharpening stone each time you change to a different type of powder.

If you apply a rough finish to the surface of a sharpening stone of less than 4 microns (4000 or above), the coarse scratches left in the whetstone will stop you getting the stone's full potential and giving your blades their intended finish. Always lap such a fine stone with fine powder at the end to produce a mirror-like finish before sharpening.