Chris Schwarz's Blog

Curved Cutting Edge Equals Tight Shoulders

Many woodworkers think it’s bonkers to use a curved cutting edge in a jointer plane. After all, the plane is designed to make things straight and flat, so using a curved cutter seems … let’s say “counterintuitive.”

But the more I use a curved iron, the more I like it. I’m always stumbling on little ways it can help me.

Today I glued up the base of a small table that has hand-cut tenons. The aprons have 4-1/2″-long shoulders, which is a lot of wood to get mated perfectly against the leg. And this is where my curved iron came in handy today.

As I was dressing the legs with my jointer plane, I did something a little odd when working the area where the aprons attach. After dressing the area to remove the toolmarks, I took three or four stokes with the jointer plane running right down the center of the leg.

This made a very small curved depression on the face of the leg , it imitated the curve of the iron. You can see this (kinda) in the photo above. It’s quite evident under a ruler to the naked eye.

When I assembled the table base, the slight curve ensured that the visible tenon shoulder would close up before the tenon shoulder on the inside of the table base. Works like a peach.

- Christopher Schwarz

13 thoughts on “Curved Cutting Edge Equals Tight Shoulders

  1. Christopher Schwarz

    David,

    This is a tough question on myriad levels. The earliest texts on planes say that the irons were sharpened straight across for jointers.

    Were they really? We do not know.

    As anyone who has worked with hand sharpening for a long time can tell you, sharpening a 2-1/4" or 2-3/8" iron straight — dead straight — is frustrating. It’s easier to sharpen a shallow camber. Add to that oil stones that might have been slightly dished and you get a situation where we are taking about how many angles can dance on the head of a pin.

    Are cambered jointer irons covered in the 18th c literature? Not that I know of.
    Are they covered in the 20th c literature? Absolutely.

    Is a very slightly cambered iron something that would be detailed in an 18th c text?

    Not sure. Ask again later.

    Does it work? Yes. Like crazy. Not just in one instance, but in many many instances over many years.

    Chris

    1. xMike

      “Add to that oil stones that might have been slightly dished…”
      That, I think, is the crux of the matter – When I was a little sprite watching my Dad and uncles work, no one had ever heard of Japanese water stones or diamond plates – they used two-sided (Carborundum) oil stones lubed with coal-oil or kerosene and the stones were ALWAYS dished from use.
      Yep, Carborundum – they only used Arkansas stones for straight razors.

  2. David

    I was just wondering, is there any historical evidence for this? I’m not saying I’m opposed, I love a cambered iron. I’ve just never taken or had the opportunity to examine any really old planes, when did the use of a cambered iron start? I recently read (to be honest, I can’t remember where I read it) that the scrub plane is a recent invention, ie. within the past two hundred years, possibly less than one hundred years). Before that, the try plane was the one to use, with the jointer being a completely different animal. From what I remember from the article, the difference was the width of the iron, and camber (apparently jointers were never cambered to ensure a tight joint). Is having a cambered iron historically accurate?

  3. Jeremy

    Chris, did you line up the crown of the plane iron with the centerline of the entire leg, or of the mortise? Maybe I’m overthinking this, but I’d be concerned that running a crowned jointer plane down the true centerline of the leg, rather than relative to the mortise, would result in the leg face being "taller" on one side of the mortise than on the other. Then you’d get the effect you want on the side of the mortise closer to the edge, but a gap on the other side. Of course, if you’re telling me that just doesn’t happen on this scale of work, I’ll take your word for it!

  4. Richard Dawson

    George wrote, "Next time I sharpen my #8 jointer, it gets a crowned profile…"

    I guess this means I need to get a #8 jointer. Oh well, OK.

    Great idea.

    Richard

  5. George Walker

    Ok, you convinced me. Next time I sharpen my #8 jointer, it gets a crowned profile on the blade. I’m sure after I execute a few joints at the bench I’ll be kicking myself for not doing this years ago. Thanks again.

    Goerge Walker

  6. Mark

    A good, sound practice. The same principle is used when coping joints in trim work, back cutting the coped piece sufficient enough to render all but the most offending out-of-square inside corners harmless.

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