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When I learned to sharpen planes, the mantra was: Bench planes need a curved cutting edge, joinery and block planes need a straight cutting edge. And in a lapse of journalistic crotchetiness, I never questioned that rationale through four presidential administrations.
A couple months ago David Charlesworth, a British craftsman, author and teacher, called to help me with another story and mentioned offhandedly how he would sharpen block planes with a curved iron. I briefly raised an eyebrow and then we plunged into some other topic.
Somehow his comment got stuck in my head and so for the last several weeks I’ve been experimenting with using a curved iron in one of my block planes. And what I’ve found is that a gentle curve in a block plane iron is a nice thing in some instances. When flushing up joints, a curved iron leaves a slightly scalloped surface like that of a smoothing plane, so there’s less (or no) follow-up scraping or sanding to do. No plane tracks.
Another advantage when flushing up joints is that you can use the curve to sneak up on an intersection of a rail and stile. In essence, you are using the fact that the tool is taking a very light cut at the edges of the shaving, which is a powerful tool. Here’s how. Let’s say that you are trimming the proud stile to be flush with the rail. By paying attention to the width of the shaving you can position the plane the thinnest part of the shaving will cross the joint line between rail and stile.
This approach put the heaviest part of the cut on the stile and just barely touches the rail, which is cross-grain to the stile. So there is much less clean up (if any) to do once the joint is flush. I found the same advantage when trimming proud end grain (such as with a rabbet) so it’s flush with the surrounding face grain.
There are times when the curved edge isn’t so ideal. I do a lot of shooting of small muntins for divided-light doors (a current project). And I really like a straight cut for the shooting process. It keeps the edges true through their thickness.
I have a few block planes, so having two shapes of irons isn’t a big deal. I sharpened one of my little block planes with a coffin-shaped body with a curve. Coffin-shaped planes are no good for shooting anyway so I won’t ever mistakenly grab a curved-iron plane for a straight-iron job.
So how much curve is correct? I sharpened it like a smoothing plane. First I clipped the corners with a file, rounding them over. Then I sharpened the iron in a honing guide using finger-point pressure. Six firm strokes at the corners. Three medium strokes at a point between the middle of the iron and the corners. Then I checked my work to make sure the curve looked good.
Next sacred cow, please.
– Christopher Schwarz
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Hello Mr Schwarz, I have just been sharpening my LN 164 blade and remembered this weblog and was wondering how much of a camber you would put on this blade or would you just "round over" the corners by applying more pressure on them for 1/2 dozen strokes. Thanks for your time
Personally, I think the block plane is an under utilized tool. Oh, I know everyone has 1, 2, 3 or more of the things. Often sitting in a drawer or on a shelf.
These days I only have 3. One, a vintage Stanley 9 1/2, has a cambered blade. Another is the LV LA block plane, but the one which is always in the shop with me when I am making a piece, is the little LN 102 bronze block plane. Lovely little bugger. Very handy.
The LV LA block I have used with a cambered blade, but now it only has the corners eased.
Well–it’s dinner. Take care, Mike
Karl,
I have always rounded the corners of my bench planes with a file. It’s a small radius. My rationale (perhaps faulty!) is that it allows me forgiveness during setup. And when I take a deep cut prevents the corners from tearing.
It’s not my idea, by the way. Saw it in a book.
Chris
Chris, are you saying that you actually file off the corners of your smoothing plane blades to get the rounding? I’ve been fighting to get the rounding at the corners of my plane blades by applying pressure to the corners during honing. It hasn’t been working terribly well…