Posts Tagged ‘dia-flat lapping plate’


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One thing I struggled with when learning to sharpen hand tools was creating the proper geometry.  Whether I was flattening a chisel back or cambering a plane iron, the results were always unpredictable.  Eventually I caught onto the fact that my stones were not as flat as I thought they were… but why not?  I was flattening them with a flattening stone after all, shouldn’t they be flat?  Isn’t that why it’s called a “flattening” stone?

My problem was the flattening stone itself was not flat.  This created non-flat waterstones which resulted if poor tool geometry.  I am making the distinction about the geometry because I think it’s important.  I was getting a perfectly acceptable polish on the tool, but not always where I was expecting it.  Poor honing (or polishing) requires a finer sharpening media, inaccurate or inconsistent honing requires a flatter sharpening media.

So down to business.  I strongly recommend avoiding the Norton Flattening Stone.  It’s inexpensive and might work at first (though don’t count on it), but it quickly goes out of flat and will do more harm than good.  “But can’t you just re-flatten the flattening stone?” you might ask… sure, if you want to burn through a lot of sandpaper on a regular basis, waste time, and always wonder if it’s time to re-flatten the flattening stone.  I’ve also heard other woodworkers and even a student of mine complain about this product, so save yourself the hassle and try one of the alternative methods I talk about below.

A granite lapping stone on the left, the Norton Flattening Stone in the middle, and the DMT dia-flat lapping plate on the right.

Notice the hollow on the Norton Flattening Stone letting light through.

Don’t misunderstand me.  I’m not bashing Norton.  I use their waterstones and use several other products they manufacture.  This stone is just not one of them.  So if you’re struggling with something as simple as lapping a chisel, your stones may not be flat.  Here are some things I would suggest you try:

-Lap your stones on sandpaper laid over a flat surface such as granite.  This is not my favorite, it’s expensive and messy, but in a pinch it works well.

-Buy a reliable lapping plate.  There are several and the are pricey.  I own the DMT Dia-Flat Lapping Plate and it can cost up to $195.  Shapton also makes a lapping plate that runs around $400.  Others use course diamond stones to lap their waterstones.  As long as the lapping stone stays flat it should work.

No light visible on the DMT lapping plate.

-Use stones to flatten stones.  I know a few people who do this (though I’ve never tried it) and they have no complaints.  If you’re on a budget, give this a shot… it’s essentially free.  The typical process would be to buy a combination stone, such as a 1000/4000 grit stone, buy a purely course (1000 grit) stone, and a purely fine (8000+ grit) stone.  Use the course side of the combination stone to flatten the purely course stone.  Then use that stone to flatten the 4000 grit side of the combination stone, then use the 4000 grit stone to flatten the 8000 grit stone.

-I know some people lap on a cinder block… that’s actually not a terrible idea except you can’t rinse it clean very easily and I would think it could be ground hollow, especially with course stones, fairly quickly.  I would avoid this method personally, but I can’t say it won’t work for you, at least temporarily.

A few more tips for flattening your waterstones: -Rinse your lapping plate between grits to avoid embedding courser grit on finer stones. -Chamfer the corners of your stones.  If you leave them sharp they will eventually chip out.  This can be done right on the lapping stone.  If you’re using the stones to flatten each other, you can’t do this so chamfer the stones on something else like a cinder block… or hey, go buy the inexpensive Norton flattening stone and use it solely to chamfer your stone’s corners… at least that’s one thing it would be useful for.

Keep it sharp. -WMT