Replies

1. 
   woodrae | Jul 31, 2007 07:08pm | #1

   Hey, Chrislac—

   That’s a fair question, but I would first ask: How much crown are you looking for? I occasionally put a crown on my blades, but it’s typically very slight and intended only to reduce track marks, which are the ridges left in the work by the two outer edges and corners of the blade.

   If you’re looking to produce big hollows in your work, then you can grind a crown on a grinding wheel or, in your case, on a piece of 150-grit (or similar; it’s not critical) sandpaper taped or glued to something flat, like a flat piece of MDF or your tablesaw’s cast-iron extension wing. I do this freehand, if necessary first marking out the desired curve on the back of the blade with a black marker, and then gently pivoting the blade by eye as I move it from side to side on the tool rest. There are commercial jigs that help with this process, but with a bit of practice, it’s faster and just as reliable to do it by hand. Check your progress with a small square held to one side of the blade.

   If you’re looking for a very slight crown, enough to reduce—or even remove—track marks, then it’s a straightforward process on your honing stones. My technique is to hone as usual, while adding a wee bit of hand pressure on one side of the blade and then on the other side as I make repeated passed over the stone. It’s a pivoting motion, and it’s easy once you try it and get the knack. I typically start with a 1,000-grit waterstone to shape and refine the edge followed by an 8,000-grit waterstone to produce a mirror polish.

   The last thing I do with a crowned blade, and with my ordinary blades, is to knock off the corners, a process called dubbing. Do this by holding the blade at roughly 45-degrees to the face of your hardest stone, and lightly dragging the blade across the stone. Make three to five passes for each corner, which rounds them slightly so they’re less likely to dig in and, again, leave track marks.

   The test for a properly crowned blade is in the pudding: Set up the plane, make a few shavings until everything is square and of the right cutting depth, then take a thin, full-width shaving that’s transparent, or stringy, on the outer edges. You should see daylight through the stringy parts, but not in the middle. Then look at your work: You’ll see very slight hollows with barely noticeable track marks.

   Good luck, and happy planing!

   —Andy