Bill Tindall
There was a recent discussion and some neat pictures on mortising. The emphasis was on what technique would be faster.

For the amateur woodworker the issue isn't speed but rather what technique is most accurate. I don't chop enough mortises that it makes any significant difference how long it takes. It follows that I am always out of practice when the need arises.

A well fit mortise has no more than 0.005" clearance between tenon and mortise. This slop allows some tiny adjustment to compensate for a mortise that is less than parallel to the face of the board(perpendicular to the edge).....but not much. Hence, the mortise must be chopped with the chisel parallel to the board face with great accuracy.

I don't find it trivial to hold a chisel parallel to the board face to +/- a degree, or what ever the tolerance is. When I assemble the frame I am overjoyed when it comes together without a rail cocked out of plane.

So, what technique of mortising is more reliable in this regard? Are there crutches that can be employed to make the process more reliable? While the technique in the video seems to be fastest, flipping the chisel around would seem to invite errors in keeping it parallel to the board face.

I happen to have some mortising needs to attend to tomorrow.