Mortising with Chisels
Steps 1 - 2
You need to cut a mortise; so which power tool will you switch on? The router, the drill press, maybe a mortising machine? Before you start setting up a power tool and searching for jigs and fixtures, consider this: You can make a fine mortise in a couple of minutes with a hammer and chisel.
You'll need the right kind of chisel, of course. Thick, sturdy mortising chisels are designed specifically to do this job. Mortising chisels come in sets of various widths, or you can just buy one and try it. We used a 3/8", heavy-duty mortising chisel from Robert Sorby (Woodcrafts, 800/225-1153).
1 Carefully lay out the dimensions of your mortise, choosing a width that matches one of your chisels. Clamp the workpiece securely to a solid surface. Then set the cutting edge squarely within the lines and 1/8" from the far end, as shown in the illustration at left. Strike the chisel with a mallet or dead-blow hammer, and drive it 1/4" into the wood.
2 Keep the bevel down, incline the chisel handle toward yourself, and begin to chop out material to a depth of 1/4", as shown at left. Pull the chisel edge back 1/8" for each new cut. Be careful not to angle the chisel left or right.
Steps 3 - 4
3 When you reach the near end of the mortise, turn the bevel edge away and set the chisel vertically 1/8" from the end line, as shown at left. Then go back to the other end and repeat step one. Continue in this way, checking the depth with a ruler or combination square, until you've reached the desired mortise depth.
4 Here's the key to cutting perfectly smooth, straight ends in a mortise -- the kind of accuracy that results in a strong, tight fit for the tenon. If your mortise is close to the end of the workpiece, find or cut a spacer block of the same thickness as your workpiece, and place it at the end, as shown at left. Clamp a 90° guide block on the layout line that marks the mortise end. Hold the flat side of the chisel firmly against this guide with one hand, and drive the chisel straight down to the bottom of the mortise.