Chopping Mortises

I started making the top for my saw chest recently.  It’s going to be a frame and panel construction with the stiles having tenons that fit into blind mortises in the rails.  Or maybe through mortises, we’ll see.

I made the frame, and wasn’t satisfied with it.  There were a few problems:

First the groove I cut with my plow plane was a little rough.  I added a wood extension to the fence on the plane to help stabilize it, and reduced the depth of cut – that seemed to take care of most of the problem.  The rest is just paying attention and keeping the cuts consistent.

Second, the tenons weren’t snug enough I think.  They weren’t loose, they didn’t wiggle around, and they fit right from the saw – but I think I want to be able to have the fit be a little tighter.

Finally, the frame didn’t lay flat when it was dry assembled.  At first I thought it was one of the tenons, but it turned out to be one of the mortises was chopped slightly at an angle.  If I assembled the frame with one corner not inserted into the mortise that stile would angle up in the air while the other three sides laid flat on the bench.  Rats.

So, three strikes and it was kindling (or as my son says “Epic Fail”).

I decided to practice chopping mortises.  The new “Make a Joint Stool from a Tree” book from Lost Art Press has some great information on chopping mortises.  I tried to apply what I read to my practice.  Now I need to go back and re-read it to make sure I didn’t miss the point.

I started by working with the chisel at an angle, with the bevel almost vertical.  One or two whacks with the mallet – I’m not trying to reach the bottom of the mortise yet.  This practice part has the groove for the panel plowed, but that has nothing to do with the mortise itself.

Then turn the chisel around so the bevel faces the other direction and make a cut to meet the first cut.

If all goes well you should have a smal triangular chip just pop out.  By the way, see that black “patina” on the tenon in the background?  That is polishing residue.  We’re going to make some shop setup changes to avoid that kind of mess in the future.

Now continue working from the sides, at an angle, until you reach the bottom.  Stay away from your layout lines  until you are at full depth for the entire width except for an 1/8″ or so at the shoulder.  With each angled cut you can go a bit deeper and still pop the chip out without trouble.  Make sure you’re holding the chisel plumb to the sides of the mortise – that was one of my mistakes.

You should be able to accumulate a pile of chunky chips fairly quickly.  This 1/4″ x 2″ mortise 1 1/2″ deep took no time at all in white pine.  I’m going to make some practice mortises in other kinds of wood for comparison.

To do the final cleanup of the bottom and get the last of the chunks out I used a swan neck chisel.

The finished mortise.  It’s not perfect, I bruised the side of the plowed groove prying a chip out, but I’m comfortable with the process now.  I think I’m ready to have another run at the lid for my saw chest now.  I also picked up some better quality pine, clear pine, at Southern Lumber.  All clear pine is 20% off for the next week!


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4 thoughts on “Chopping Mortises

  1. Great post! Did you see the jig for chopping mortises in the latest PWW mag?

  2. I tried a mortise with bench chisels after watching Paul Sellers do it. I had the same problems with square and such. Mine was a through mortise. Is the pig sticker you’re using an old one?

  3. Ralph, I think part of the problem with keeping the chisel plumb to the (intended) mortise walls is that when I’m chopping a mortise my inclination is to have the mortise layout running side-to-side in front of me — but from that orientation it’s hard to tell if the chisel is plumb. I bet changing the orientation of the board so I’m sighting down the length of the mortise would eliminate problems like that.

    And yes, this is a “pig sticker” style chisel. It was a bit over 1/4″ and rusty, I stoned it down to exactly 1/4″. I really like this style of mortise chisel, although it’s overkill in this squishy white pine.

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