Expert Answers: Flattening Water Stones with a Diamond Stone

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This article is from Issue 92 of Woodcraft Magazine.

Q: I bought a coarse diamond sharpening stone to flatten the water stones that I rely on for sharpening chisels and plane blades. But the diamond stone seems to have lost its effectiveness. Am I better off using a different flattening method?

A: A coarse or (better yet) extra coarse diamond stone will flatten any water stone. But you can expect the diamond stone to wear more quickly than it would if you’re just sharpening steel. The best type of diamond stone to use for flattening water stones is a diamond lapping plate designed for this single purpose. The DMT Dia-Flat® lapping plates rely on a proprietary hardcoat treatment that fuses diamond particles more solidly to the plate’s metal base to avoid premature wear. Because diamond flattening plates are expensive ($135-$380), some woodworkers opt to flatten water stones using a grooved flattening stone that typically sells for under $50. 

Make sure to soak the water stone before a flattening session, and mark pencil lines across the length of the stone so you can track your progress. If your flattening plate is larger than your water stone, place the flattening plate (or flattening stone) on a level surface and rub the water stone in a circular motion over the plate. If your flattening plate is smaller than your water stone, reverse the orientation. Whether you’re using a diamond flattening plate or a grooved flattening stone, it’s important to rinse away loose abrasive material frequently as you flatten.

John Carmona

Woodworker and founder


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