How to Cut Mortise With a Chisel
Before routers and other power tools sped up woodworking, cabinetmakers cut mortises the classic way, using a chisel and mallet. A special mortising chisel is thicker than other chisels and has parallel sides that help it cut straight down into the grain of wood. A well-appointed woodshop includes several of different sizes, matched to the different widths of mortises, though you can substitute a regular chisel of the right width if necessary. Use a mallet rather than a metal hammer to hit the chisel so you don't damage its handle.
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Instructions
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Draw a rectangle on the wood to mark the opening of the mortise, using a square to make sure it's aligned with the edges of the wood. Choose a width that's the same width as the mortising chisel you plan to use. If you have a marking gauge, set it to mark the sides of the mortise and use it to scribe the lines.
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Measure the depth of the mortise on the chisel with a ruler, starting at the tip, and mark the depth with a piece of tape. Place the bottom edge of the tape on the mark so you won't scrape off the tape as you work.
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Clamp the wood at a comfortable height with the bottom resting against a firm surface and the top of the mortise upward.
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Place the chisel near the center of the mortise, slanted toward the center, and tap it with a mallet. Move it to the other side of the center, slanted toward the previous cut, and tap it again, chipping out a piece of wood. Repeat, gradually widening and deepening the hole until you reach the full depth of the mortise as measured by placing the chisel vertically in the center of the hole and noticing the bottom of the tape aligned with the surface of the wood.
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Place the chisel vertically against the line marking one end of the mortise so the bevel is toward the center of the mortise. Tap the chisel with the mallet to drive it straight down, cutting away the wood to make the end of the mortise vertical. Repeat for the other end.
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Check the width of the side walls by sliding the chisel along the mortise or using a piece of wood cut to the size of the tenon. Pare off any excess wood with the chisel so the side walls are vertical, parallel and just wide enough.
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Tips & Warnings
If you're cutting a large mortise, remove some of the wood before starting by drilling down to the depth of the mortise with a drill slightly smaller than the width of the mortise, using a drill press to keep it vertical.
A swan-neck chisel, made with a curve in the shaft so the blade is at an angle, makes cleaning out the bottom of the mortise easier.
References
Resources
- Photo Credit Ciseau 3 image by rolero54 from Fotolia.com
