Wednesday, October 2, 2013

Why camber?

Someone recently asked for help on a forum because they were struggling to joint a square edge using a just refurbished #6 with a cambered blade.  I replied that when this happens to me it is generally cockpit error and that I don't camber blades on planes I use for jointing.  That got me thinking about camber.

Truth is, I didn't camber any of my dozen or so plane blades for a long time.  I am a person who learns best when I understand why (You know the little kid who asks why, why, why constantly?) and I hadn't read an explanation that appealed to me.  I also believe in the 80/20 rule, so my thought was, "If I can get a nice straight sharp edge, that works for me.  Why should I take the complicating step of cambering the blade?"  Recently, though, a light went on for me and I think I have an explanation that works for me.  Tell me what you think.  I realize that this is likely obvious, but it hadn't occurred to me.

The light went on when I was carving spoons with a stout #8 gouge following Paul Sellers.  Carving cross-grain with a blade that I could see told the story.  You get nice, clean scallops even when taking deep cuts because the gouge severs the fibers on both sides.  Try the same thing with a flat chisel and you get a mess, random deep tearout and a completely unpredictable surface.  I immediately decided to camber plane blades that I use cross-grain.  For me, this is one of my #5s and my #6.

As I've already written, I don't camber the blade in my jointer, but I also don't camber the blades in my #3 or #4 either and I think this runs counter to the accepted wisdom.  The justification I have read for cambering smoothers is that this will eliminate plane tracks.  I haven't found this to be a problem because I finish smoothing with very light cuts and any plane tracks are quickly removed with a scraper.  I do realize that some of you go directly from the plane to finish and that it would make sense for you to camber your smoother blades very slightly, perhaps .002".  I do sometimes finish sharpening sometimes by applying pressure on each side of my smoother blade successively and perhaps that is what is meant by cambering a smoother blade.  I cheerfully admit that I am incapable of producing a .002" camber any more precisely.

A friend of mine recently acquired a number of 5 1/4s from a local school and a box of over 100 blades, every one of which was heavily cambered.  This puzzles me.  This was the only plane in the school shop.  Why would the teacher camber every single blade?  I seriously doubt they were using rough lumber that they prepped by hand.  This seems like a terrible idea to me, but perhaps one of you can explain.


  1. Andy, a plane with a cambered blade produces a shaving that tappers to zero at each edge. When jointing the edge of a board that is out of square you can control how much material you are removing, and from where on the edge, by moving the plane stroke back and forth laterally on the edge of the board. This is easier and more accurate than trying to tilt the plane or constantly readjusting the lateral lever.

  2. The only cambered iron I have is on my #6 which I used for prepping rough sawn stock. All my other planes are all square including my #5. I file a slight radius on the edges of my straight planes. Another thought on square irons is I don't do the ruler trick or do a micro bevel.
    My thoughts on cambered irons: How can you square the edge of a board across it's face for edge jointing with one?

    1. Accidental--
      Cambered irons have a use as you mentioned, roughing with your 6, most use this camber on a jack or 5 but I also lightly camber my smoother so I don't leave track marks in my smooth finish.