Mortise-and-tenon joints are inherently strong, but for a little extra reinforcement they can be pinned with through dowels. A pinned mortise-and-tenon joint is ideal for high-stress joints, like those found where vertical and horizontal furniture members are joined.
There are two basic methods for constructing a pinned (sometimes called pegged) mortise-and-tenon joint. One is to bore a hole through the tenon and another through the mortise before the joint is assembled. If you offset these holes slightly, the joint will be drawn together tightly when the dowel is driven through it. A more common method is simply to drill a dowel hole through the joint after it is glued and assembled, as shown here. This type of pinning doesn’t contribute greatly to the strength of the joint, but it does provide a valuable back-up in the event that the glue joint fails.
The exposed ends of dowels provide a nice decorative detail, especially when they’re oriented so the grain runs in the opposite direction of the board the dowel is set into.
How to make pinned mortise-and-tenon joints.
1. Cut the mortises and tenons. then glue and clamp the joint. Let the glue set up then lay out the location of the pins with a pencil and combination square. Use at least two evenly spaced pins for each joint, making sure the guide holes are at least 3/8 in. from the edges of the boards.
2. Punch a small starter hole at the centerpoint of each pin hole. if your project is a manageable size, use your drill press to drill the holes, as we did hi the photo above. Using a brad-point bit will ensure that the hole starts precisely in the centerpoint. Drill the holes all the way through the tenon and into the other side of the mortise. Use a bit stop If your plan calls for stopped pins. if you’re creating through-pin joints, drill all the way through the joint and into a piece of scrap.
3. Cut the pins from hardwood dowels, normally of the same species Islas the workplaces. Tip: For a decorative touch, use dowels made of wood with a naturally contrasting wood tone (for example, maple pins driven into walnut workpieces). Taper the lead tip of the dowel slightly so it will enter the hole more easily. Squeeze a little glue into each hole, then tap the dowel pins home with a wood mallet. Stop tapping when the dowel seats at the bottom of the hole.
4. Trim the dowels flush with the leg surface—here we use a flexible, fine-tooth Japanese-style saw. Depending upon the amount of dowel you need to remove, you may be able to smooth the ends flush with a file instead of sawing them off.
5. Finally, remove any excess glue with a scraper and sand the surface smooth with sandpaper and a wooden sanding block.