Woodworkers, such as chairmakers who depend on mortise-and-tenon joints, sometimes keep a dehumidifier in their shop to make it drier than the surrounding environment. Once inside the shop, wood shrinks slightly. When a completed project is returned to normal humidity, the tenons swell in the mortises, making the joints tighter.
5-1 The mortise and tenon is an extremely versatile joint, and many forms have evolved for various purposes. In the through mortise and tenon (1), the tenon passes completely through the mortised member; the end of the tenon is not visible in the stopped mortise and tenon (2); in the keyed mortise and tenon (3), the tenon is held in the mortise by a wedge or "key;" the adjoining parts of the haunched mortise and tenon (4) are grooved to hold wooden panels; the round mortise and tenon (5) is used to assemble turned parts; the dovetail mortise and tenon (6) is so called because a dovetail-shaped tenon rests in an identically shaped mortise.
There are many different ways to make a mortise, but well concentrate on three of the easiest. Perhaps the simplest of all is to use a drill press. Lay out the mortise, remove as much waste as possible by drilling overlapping holes, then clean up the sides and corners with a chisel. (See Figures 5-2 through 5-4.) If you have less than a dozen mortises to make, this is an excellent method. And because there is little setup time, it's very quick.
5-4 Remove the remaining waste from the sides and ends of the mortise with chisels. Use an ordinary' beveled-edge paring chisel to clean up the sides and — if you have one — a mortising chisel to square the ends.
5-3 Select a bit diameter that matches the width of the mortise you want to make. (Some woodworkers prefer to use a bit that is slightly smaller.) Mount the bit in the drill press and bore overlapping holes to remove most of the waste from the mortise. Don't space the holes too close; the bit may drift. If you wish, clamp a straightedge to the drill press to guide the stock. This will keep the holes in a perfectly straight line.
5-2 To make a mortise on a drill press, first lay out the joint on the stock with a marking gauge and an awl. In addition to marking the perimeter of the mortise, scribe a line down the center to help position the drill bit.
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When cleaning up a mortise, use a mortising chisel to square the ends or remove large amounts of stock. Most chisels are designed to be used alternately as a cutting tool and a wedge — you cut down through the grain, then split out the waste. A mortise leaves little room to work in this manner, so a mortising chisel splits as it cuts. The thick blade with its steep bevel pushes the waste to one side as you cut down through the wood. Note: Always place the cutting edge of a mortising chisel across the wood grain.
You can also use a hand-held or table-mounted router and a straight bit to cut a mortise. Simply rout a double-blind dado in the stock, then square the blind ends with a chisel. (See Figures 5-5 through 5-10.) This method requires more setup time, but saves cutting time, particularly if you have a lot of mortises to make. The drawback is that you can only make relatively shallow mortises, no deeper than the router bit will reach.
When routing a mortise, make the recess in several passes. Remove just Va to lA inch of stock with each pass — remember that routers and router bits aren't designed to remove large amounts of stock all at once. If you have a lot of mortises to rout, adjust the router to cut no more than lA inch deep. Cut all the mortises in all the workpieces to this depth. Increase the depth of cut and rout all the mortises again. Continue until you have routed the mortises as deep as you want them.
Steep Bevel Morti5INj& Splits Out Chips
5-5 To rout a mortise with a hand-held router, make a frame to guide the router. Clamp the frame to the workpiece and rout the mortise, keeping the base of the router inside the frame. The inside dimensions of the frame will control the length and width of the mortise. Note: If you have one, use a plunge router when performing this operation. Otherwise, you may want to drill a stopped hole that's a little larger than the router bit into the middle of the mortise. This will provide a place to start routing.
Steep Bevel Morti5INj& Splits Out Chips
"Tip Cuts Wood Grain
If you wish, use a mortising fence to make multiple mortises. This jig has adjustable stops at both ends to automatically start and stop mortise cuts, and can be used on both a drill press and a router table. Plans and instructions for making this "Mortising Fence" are on page 67.
5-7 When routing a mortise on a table-mounted router, its difficult to know where to start and stop since you can't see the cut as it progresses. To remedy this situation, make several alignment marks where they will be visible on both the machine and the workpiece. First, put a piece of tape on the fence or on the work surface of the router table. Using a small square, mark the diameter of the bit on the tape.
5-6 You can also use a guide collar and a template to make a mortise with a hand-held router. Mount the guide collar on the router sole with the bit protruding through the center. Clamp the template to the workpiece and rout the mortise, following the inside edges of the template with the collar. This setup is especially useful for routing small mortises.
5-8 Next, use the square to transfer the layout lines that mark the length of the mortise to another surface on the workpiece. This surface must be clearly visible when you cut.
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