What the draw actually does
Bore a hole through the mortise cheeks. Assemble the joint dry and push a bradawl or a transfer punch through that hole to mark the tenon. Then take the tenon out and bore its hole a little closer to the shoulder than the mark — a sixteenth is a figure people use, and the right figure is a design decision. When the joint goes back together the holes no longer line up. Driving a peg through forces them into line, and the only way they can come into line is for the tenon to move deeper into the mortise, which pulls the shoulder hard against the post and keeps it there.
That is the whole mechanism, and it explains why the offset is small. The peg has to bend through the misalignment as it is driven. A peg that has to bend too far breaks instead of pulling, and it breaks inside the joint where you cannot get at it. A peg that has nothing to bend through does not pull at all. The useful range is narrow, it depends on the species of both the peg and the timber, and it is not a number a web page gets to hand you.
Relish is where a drawn joint fails
Relish is the wood between the peg hole and the end of the tenon. Load the joint in tension and the peg presses on that wood; if there is not enough of it, the peg tears a channel straight out through the end of the tenon and the joint comes apart while the peg is still perfectly intact. It is a shear failure along the grain, and long grain in wood is exactly where shear is weakest, which is why the relish figure gets more attention in timber framing than the tenon dimensions do.
The arithmetic is simple and worth writing out: relish is the tenon length, minus the distance from the shoulder to the hole centre, minus half the peg diameter. Draw boring makes it slightly larger than it would otherwise be, because moving the hole toward the shoulder moves it away from the end. At the defaults on this page — a 4-1/2 inch tenon, the first hole 1-1/2 from the shoulder, a second hole 2 inches beyond that, a 1 inch peg drawn 1/16 — the last hole sits 3-7/16 from the shoulder on the tenon and the relish is 9/16.
| Distance | How it is measured |
|---|---|
| Edge distance | shoulder to the hole centre, along the tenon |
| Draw offset | post hole centre to tenon hole centre |
| Relish | hole edge to the end of the tenon |
| Peg length | timber width plus the projection at both ends |
Why pegs get counted separately
A modest frame has dozens of pegged joints and most of them take two pegs, so a four-bent frame can want a hundred and fifty pegs before spares. They are not a fastener you buy by the box in the size a particular frame wants, they are usually riven out of straight-grained stock and shaped, and they break. Fifteen percent spare is a working margin rather than a rule; a species that splits easily or a driver having a bad day will eat more. The count and the stock length matter because peg-making is a batch job you would rather do once.
What this page does not know
It does not know your species, your peg species, the loads on the joint or the code your jurisdiction adopted. It places holes at distances you supplied and subtracts to find what is left. Every warning it prints is a description of a geometry — the relish is under one peg diameter, the draw is over a quarter of the peg diameter — and not a verdict on whether the joint is adequate. Those verdicts belong to the engineer or frame designer who specified the joinery.
Questions people ask
How much draw should I use?
It is not a number this page supplies, and it genuinely varies. It depends on the species of the timber and of the peg, the peg diameter, how green the timber is and how the joint is loaded. Too much and the peg shears while it is being driven; too little and the joint is not pulled closed. Take the figure from the frame designer or engineer who drew the joinery, and if you are working from a design that does not state one, that is a question to ask rather than a gap to fill in yourself.
Which way does the tenon hole move?
Toward the shoulder — that is, back along the tenon in the direction of the rest of the rail. Moving it the other way pushes the joint apart instead of pulling it together, and because the mistake is invisible until the peg is going in, it is worth marking the direction on the timber before boring. The offset also increases the relish rather than reducing it, which is a small bonus.
What is relish and why does it get its own line?
It is the wood between the peg hole and the end of the tenon. It is the material that stops the peg from tearing out lengthwise through the tenon end when the joint is pulled, and because that failure runs along the grain it happens at loads far below anything the tenon itself would care about. It gets its own line because it is the dimension people most often lose without noticing, usually by moving a hole to clear something else.
Why is the peg longer than the timber it goes through?
So there is something to hit and something to grip. A peg driven flush has to be started perfectly and cannot be pulled if it goes wrong, and the ends are usually trimmed after the frame is up rather than before. The projection field is that allowance at both ends. Set it to zero if your detail calls for a flush peg.
Can I use a bolt instead and skip all this?
That is a structural question with a structural answer, and it is not one this page can give. A bolt in a hole behaves differently from a driven wooden peg in almost every respect that matters — bearing, slip, how the connection behaves as the timber shrinks around it, and how it is designed. Whether a connection may be substituted is decided by the engineer or frame designer and by the code in force where you are building.