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I am planning to order a corner chisel, to use when I install hinges, and have
seen several styles.  Which do you prefer?

That’s a question I received from a reader, and the picture above shows the scenario he’s asking about. The piece of wood has a routed mortise with rounded corners. The corners need to be square for a hinge to fit, and the chisel he asks about is supposed to make this easy. As much as I like tools, this is one that nobody really needs. It’s a crutch that will actually keep you from developing a simple skill. A plain old chisel will remove the excess wood in the corner quickly and easily.

I routed the mortise deeper than normal to better show what happens with the chisel. The process works better if the layout lines are incised with a marking knife or gauge as well as a pencil. I recommend a mechanical pencil, but I don’t recommend the girly color unless you have a teenage son who habitually picks up every pencil he sees.

The key to doing this is to use the back of the mortise cut by the router, or the incised layout lines as a guide to place and align the chisel. I line up the corner, then pivot the chisel back toward me so that it is against the back edge of the mortise.

Making the actual cut is as simple as pivoting the chisel back down into the corner. The fingers of my left hand hold it in place while I push down on the end with my right hand. This is a finesse move, not a forceful one, and depending on the hardness of the wood it may take a few swings to reach the desired depth.

Coming the other way, you often don’t have enough of a straight edge to register the back of the chisel, but if the knife line is there, the edge of the chisel will fit. Again I start by putting the corner of the chisel on the corner of the mortise. When the back of the chisel is vertical, I plant my left hand to keep the chisel in line and push down with my right. This cut will offer more resistance, but a few seconds of pushing and wiggling make the cut.

A little bit of junk will be left in the corner, and it’s easily removed with a paring cut or two. Working toward the end allows you to push harder with the bevel of the chisel down. The paring cut can also be made with the bevel up, working at a right angle to the direction shown in the picture. The caution with that method is to push gently. There isn’t much wood behind the mortise, and an agressive cut can split out the back.

After you do this a few times it will become second nature, taking less time than it takes to describe the process. So save your money for the tools you really need.

Bob Lang

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Showing 6 comments
  • Charles M

    Hi all. I would encourage you to “think beyond the square” (pun intended). It only takes about 2 seconds to round the corners of a hinge on the bench grinder for a perfect fit to a round-cornered mortise created by a router. For a lousy woodworker like me, it’s far easier to modify the steel than risk breaking out the back of the mortise with a chisel by mistake. (I’ve ruined a lot of doors!)
    If you simply must have a square-cornered mortise, nip the corners out of the timber with an oscillating multi-tool – even quicker than grinding the hinge.

  • Joe Lyddon

    I have often wondered about this…
    I have always thought a good ole chisel would be better…

    Now, I KNOW!

    Thank you very much!

    Very good tutorial & pics!

  • Tom

    I was given one of those spring-loaded corner chisels you whack with a mallet. I used it – maybe – twice and have yet to be impressed with the results. Now, it collects dust while I use my Marples chisels to get nice square corners.

    Hey, the chisel is one of those essentials!

  • Neil

    Hi……this is my 4th trip back to this post, I wanted to comment when it was first posted but didn’t want to bring up the corner chisel, but kept coming back because this is an excellent "hinge chisel work tutorial post" (mouth full) A woodworker reads this and he’ll see the corner chisel as non-essential.


  • Rob Porcaro

    Bob, I heartily agree with your answer!

    Corner chisels have two big problems in my view. First, when set into the corner for the final cut, you’ve got no margin for error. The cutters are at 90 degrees so if you cut one edge conservatively, the other is over cut.

    Secondly, they are a major pain to sharpen and still retain good edge geometry at the point where the two cutting edges meet at 90 degrees.

    This is why the only corner chisel I have ever owned has long since been discarded and I’ve never missed it.

  • Mattias in Durham, NC

    You are right, Sir. This is pretty comical to me though since I threw in a "corner cutter" with an online order the other day just because it was so darn cheap. It is still in the mail. I should have resisted the urge.

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