Q:

I use waterstones to sharpen my tools and have heard that diamond stones are a great way to flatten them. I’d like to give it a try, but I’m worried that a coarse diamond stone will ruin my polishing stones. Which grit of diamond stone should I use?

Todd Cook, Spring HIll, FL

A:

When choosing a diamond stone for lapping. look for one that is flat, coarse, and larger than your stones. I use a 120-micron diamond stone that is roughly equivalent to P120-grit sandpaper. It flattens the waterstone quickly without any ill effects. You might see tiny scratches on your stone, but those won’t diminish its performance.

You also want the diamond stone to last for a long time, and some wear quickly, coming out of flat and losing their grit much sooner than you would think (to read more on a diamond plate designed to flatten waterstones, see FWW #223). That’s why it’s best to use the diamond stone only for lapping your sharpening stones, since that spreads the wear over a broad surface rather than focusing on smaller areas with a blade or chisel.

Bigger is better. A large diamond plate works the entire surface of the stone at once, so it’s sure to be dead flat.

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