Dowel joint
Also called: dowel, dowelled joint, dowelling, dowel pin
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A dowel joint holds two pieces of wood together with short, round wooden pegs, known as dowels, that are glued tightly into matching holes bored in each piece so the two faces line up and cannot slide or twist against each other. Audels (1923) treated it as a plain butt joint, simply two squared ends brought together, reinforced with pins bored through both pieces to keep them aligned, and offered as a cheaper stand-in for a mortise and tenon.
Making and fitting the pins
Dowel rod can be bought ready made. Jones (1920) noted that the ready-made birch dowel rod was commonly used, and that "a bit must be found for boring holes into which the rod will drive rather tightly": the peg should be a snug, driven fit, not a loose one. A joiner could also make pins by hand. Ellis (1908) described pins cut from "some tough hardwood such as oak or beech, cleft in the direction of the grain", roughly rounded, pointed, then driven through a dowel plate, a steel plate pierced with graded round holes that trims an oversized peg down to an exact, round diameter. Hasluck (1897) recorded the same kind of plate being used by coopers to shape the dowels that pin cask heads together, and dowelling bits being used by table makers boring the holes for the pegs that join the leaves of a table. Many dowels also carry a shallow groove or a set of rolled flutes running along their length. Porter (1999) explained that this channel lets trapped air and surplus glue escape as the peg is driven home, rather than the glue simply jamming the joint before it seats; Noll (2002) added that some woodworkers roll the rod under a saw held at an angle purely to leave saw tooth marks, on the theory that the ridges give the dried glue something to key into. To lay a hole out accurately, Ellis (1908) had the joiner lay the two pieces together back to back and mark through both at once, while a later method uses metal dowel centres: points pushed into the holes already bored in one piece, then pressed against the mating piece so each point pricks the exact matching centre. Once the glue has set, any dowel left proud is commonly sawn off flush with the surface.
Fit and strength
How deep a dowel needs to go, and how well it holds, both depend on how the hole is bored relative to the grain. Joyce (1987) put the working depth at around thirty-two millimetres for a peg to hold well, with a little clearance left at the bottom of the hole for surplus glue, and recommended driving the dowel home flush on one edge before checking its projection against the matching socket in the other piece. Fairham (1920) likewise called for "a very slight countersinking at the joint of the board", so that a dowel left minutely proud does not force the two faces apart. Grain direction matters more than depth. Noll (2002) pointed out that where a dowel sits surrounded by long grain, running the length of the hole, the glue has a large surface of open wood cells to bite into and the joint is strong; where the hole instead crosses mostly end grain, there is little of that long-grain contact, and the joint is left weak against being pulled apart and against the glue line shearing under load. This is why a dowel joint is chosen with care for where the load will fall, rather than used as an automatic substitute wherever a mortise and tenon would once have gone.
Where dowels are used
In door and window making, Brett (2005) explained that dowelling cuts cost against a mortise and tenon in three ways, among them shortening each rail by at least two hundred millimetres, and that a haunch, a short stub of timber worked into the corner of the joint for extra resistance to twisting, is often added alongside the dowels rather than relied on alone. Foundry patternmakers used dowels for a different purpose: Jones (1920) described marking the dowel hole positions on the joint face of a pattern or core box, then transferring those same centres to the opposite half, so that the two halves of the mould always line up. The joint is older than any of these trades. Sturt (1923), recalling work in a wheelwright's shop, remembered that "the dowel-holes were at an obtuse angle with one another" at an early stage of assembling a wheel, "before the felloes had been rapped down into their place": the curved rim sections, or felloes, of a wooden wheel were doweled together long before glued dowel joints became routine in cabinet and joinery work. Engineers now treat the dowel as one member of a wider family of fasteners. The USDA (2021) wood handbook groups nails, screws, bolts and lag screws together with plain dowels under a single heading of dowel-type fasteners, and works out how much load each will carry from a property it calls the dowel bearing strength of the wood.