Making Treenails — Wooden Pegs for Timber Framing and Shipbuilding

Before iron nails were cheap, wood was fastened with wood. A treenail (pronounced 'trunnel') is a cylindrical wooden peg driven into a bored hole to lock a timber joint together. Treenails held together medieval roof trusses, Viking longships, and post-and-beam barns for centuries. In many applications they outperform iron nails — they do not rust, they swell when wet to tighten the joint, and they flex with the timber instead of working loose.

Treenails are always made from a wood harder or at least as hard as the timber they join. Oak treenails in oak frames, or locust treenails in softwood construction. They are riven from straight-grained stock, never sawn — riving preserves the grain continuity that gives the peg its shear strength. A sawn peg has cut fibres that snap under load.

The technique is simple: rive a billet into rough square sections, then round them by driving through a steel plate with a round hole (a rounding die) or by shaving with a drawknife. The finished treenail is slightly tapered so it can be started in the hole and driven home with a mallet. Some traditions split the protruding end and drive a small hardwood wedge into the split, locking the treenail permanently.

初学者

1-2 hours (for a batch of 20-30 pegs)

说明

Select straight-grained hardwood

Choose a piece of oak, ash, locust, or similar dense hardwood with perfectly straight grain and no knots. The grain must run the full length of the peg without deviation — any cross-grain weakness means the treenail will snap under shear load. Green wood works best for riving. You need a billet about 30-40 cm long and at least 8 cm in diameter to produce a useful batch of pegs.

Rive the billet into square blanks

Split the billet lengthwise into quarters using a froe or wedge, then split each quarter into pieces roughly 2-3 cm square in cross-section. The exact size depends on the hole diameter you are pegging — the blanks should be slightly larger than the finished peg. Each split must follow the grain precisely. Discard any blanks where the grain runs out the side — these will be weak pegs.

所需工具：

Froe

Round the blanks

Each square blank must be rounded to fit a bored hole. The traditional method is a rounding die — a thick iron plate with a round hole slightly smaller than the blank. Place the blank on the hole and drive it through with a mallet. The plate shaves off the corners and produces a cylindrical peg in one stroke. Without a die, use a drawknife on a shave horse to whittle the blank round, turning it frequently to keep the cross-section circular.

Taper the leading end

Shave a slight taper on one end of each peg — about 2-3 cm of gradual narrowing to a blunt point. The taper lets the peg start in the hole and self-centre as it is driven. Do not sharpen to a point — a sharp tip splits the surrounding timber. The taper should be gentle enough that the peg contacts the hole walls within the first centimetre of driving.

Bore the holes and drive the treenails

Bore holes through the timber joint with an auger. The hole diameter should match the peg diameter closely — a loose peg has no holding power. In traditional timber framing, the hole in the tenon is offset slightly from the hole in the mortise (draw-boring). When the treenail is driven through both, it pulls the joint tight. Drive the peg with a wooden mallet, not a metal hammer — metal mushrooms the end of the peg. Drive until the peg is snug and flush or slightly protruding.

所需工具：

Hand Auger

Wooden Mallet

Wedge the protruding end (optional lock)

For a permanent joint, let the treenail protrude 1-2 cm beyond the far face of the timber. Split the protruding end with a chisel and drive a thin hardwood wedge into the split. The wedge expands the end of the peg inside the hole, making it impossible to pull out. This is the same principle as a through-wedged tenon. In shipbuilding, treenails were always wedged on both ends — the inner end wedged before the plank was offered up, the outer end wedged after driving.