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Drawboring is one of the few joinery tricks that makes a joint tighter every time it is assembled. The peg holes in the mortise and the tenon are deliberately misaligned by a small amount. When the tapered peg is driven through both, it catches the edge of the offset hole and pulls the tenon deeper into the mortise, closing the shoulder under force a clamp would struggle to match.
Get the offset right and the joint locks itself, with or without glue. Get it wrong in one direction and the peg does nothing; get it wrong in the other and the stile splits. The difference between the two is often less than 1/16 inch.
What Drawboring Does That Glue Cannot
A glued mortise and tenon depends on the glue line and the clamp pressure that held it during cure; once the clamp comes off, only the bond remains. Seasonal movement works on that bond every year, and a joint that was tight in July can develop a hairline at the shoulder by February.
A drawbored joint adds a mechanical lock. The peg passes through the stile, the mortise, the tenon, and the far cheek of the mortise. Because the tenon hole is offset toward the shoulder, the peg bears against the tenon and pulls the shoulder hard against the stile. The joint is held by wood bearing on wood, not just glue. A drawbore is not the only way to lock a tenon with wood; a wedged mortise and tenon uses a similar principle at the end of the tenon instead of through its cheek.
The Offset Is the Whole Trick
The offset is the distance the tenon hole is shifted toward the shoulder relative to the mortise hole. A typical offset is 1/16 inch (1.5 mm) for furniture-scale work, 3/32 inch for larger joints, and 1/8 inch at the upper end for heavy frames. Softwoods compress more and can take a slightly larger offset; dense hardwoods and thin tenons want less. Too little and the peg slides through without pulling the joint. Too much and the peg has to bend or crush its way through, which can split the stile or snap the peg.
The tenon hole moves toward the shoulder, which is toward the rail and away from the end of the tenon. When the peg enters from the stile face, it passes through the mortise hole first, then meets the tenon hole. Because the tenon hole is closer to the shoulder, the peg bears on the far side of that hole and pushes the tenon in the direction that closes the joint. Mark the direction on the tenon with a pencil arrow before drilling; a 1/16 inch error in the wrong direction turns a drawbore into a joint that pushes itself apart.
Peg Selection and Shaping
Use a riven hardwood peg, not a dowel. Riven stock follows the grain, so the peg is strong along its whole length and does not have the short-grain weakness that makes dowels snap. White oak, ash, hickory, and black walnut are traditional choices. The peg should be straight-grained, with no runout visible on the side, and dry, ideally at 6 to 8 percent moisture content, slightly drier than the frame so it swells after driving. Verify that with a moisture meter reading rather than trusting the lumber sticker.
Diameter is usually 3/8 inch for furniture and 1/2 inch for benches and frames. The peg should be slightly larger than the drilled hole, by about 0.005 to 0.010 inch, so it compresses the fibers as it enters. A peg that drops in will not hold; one that must be hammered hard from the first tap is too large. Shape one end into a gradual taper, about 1/16 inch reduction over 2 to 3 inches, and chamfer the tip so it starts easily and tightens as it goes.
Laying Out and Drilling the Mortise
Position the peg hole through the mortise cheek, centered on the stile thickness and set back from the shoulder by roughly one-third of the tenon length, or about 1/2 to 1 inch on typical furniture. Keep the hole at least 1-1/2 peg diameters from the end of the stile and from the edge of the mortise. The hole passes through the mortise void, so the drill has to be supported on both sides to avoid blowing out the far face.
Mark the center on both faces of the stile with a marking gauge or square, then drill from one face with a brad-point bit. Clamp a backer board to the far face to catch the exit and prevent tearout. The hole should be a close fit for the peg: drill it with a bit the same size as the peg's nominal diameter, then test the peg before moving on. The mortise gauge setup already establishes the centerlines; carry them around the stile with a square so the peg hole stays in the same plane as the mortise. The mortise walls also need to be straight and square, which is the part of chopping a mortise by hand that rewards a sharp chisel and a light final pass.
Transferring the Offset to the Tenon
Assemble the joint dry, with the tenon seated against the shoulder. Insert a brad-point bit or transfer punch through the mortise hole and press it into the tenon to mark the center. Take the joint apart and look at the mark; that is the aligned position. The drawbore hole goes 1/16 inch toward the shoulder from that mark.
Set a marking gauge to the offset and scribe a new centerline, or shift the punch mark with a combination square. Center-punch the new position, then drill through the tenon with the same bit, supporting the far side with a backer. The hole must go through the tenon square to its face; an angled hole will make the peg bind and can split the tenon along the grain. For a through mortise and tenon, the tenon hole only needs to pass through the tenon, not the far stile. If the far cheek is thin, drill it slightly oversize or chamfer the exit so the peg does not split it. The through mortise and tenon method covers keeping the cheeks and shoulders clean before the peg goes in.
Driving, Trimming, and Listening
Do a dry assembly with the peg before glue. The peg should start with a few taps and then tighten noticeably as the taper engages. The shoulder should close against the stile with light mallet pressure, and the peg should not bottom out before the joint is tight. If it goes in too easily, increase the offset or use a slightly larger peg. If it will not start, reduce the offset or slim the taper.
For final assembly, glue the shoulders and cheeks, but leave the peg dry or give it only a thin smear of glue. A dry peg relies on friction and swelling. Support the far side of the stile with a heavy block or dead-blow mallet so the force goes into the joint rather than the frame. Drive with firm, square blows and listen for the sound to change from a hollow tap to a solid thud; that means the peg has seated. Do not overdrive. Trim the peg with a flush-cut saw, then pare or plane it flush after the glue cures. The trimming cut is a paring job, not a chopping one, and the distinction is covered in paring versus chopping technique.
Taking the Joint Apart Again
Drawbored joints are repairable, which is one of their advantages. Drill out the peg with a bit slightly smaller than the peg diameter, then collapse the remaining shell with a small chisel or punch it out from the far side. Work from the exit side, and support the stile around the hole so the drill does not tear the surface. If the joint was glued, expect to re-glue the shoulders when it goes back together.
Troubleshooting
The shoulder will not close. The offset is too small, or the tenon hole was drilled on the wrong side of the mark. Test the offset on scrap. If the tenon hole is offset away from the shoulder, the peg pushes the joint apart; redrill on the correct side and plug the old hole.
The peg snaps. Short grain, a taper that is too abrupt, or an offset so large that the peg has to bend sharply. Use riven stock, lengthen the taper, and reduce the offset.
The stile splits. The peg is too large, the hole is too close to the end or edge, or the offset is excessive. Test the offset on scrap and keep at least 1-1/2 peg diameters of edge distance.
The joint loosens after a season. The peg was too wet when driven and shrank, or the offset was too small to maintain tension. Replace the peg with dry stock and a slightly larger diameter. Wood movement is relentless, and the rules for designing joints around movement apply to pinned joints too.
Frequently Asked Questions
How much offset should a drawbore have?
About 1/16 inch for typical furniture joints, 3/32 inch for larger work, and no more than 1/8 inch. Dense hardwoods and thin tenons want the smaller end of that range. The right offset makes the peg require a firm tap and pulls the shoulder closed without crushing the tenon.
Can I drawbore without glue?
Yes. A drawbored joint is a mechanical lock and many traditional frames are assembled dry. Glue adds security at the shoulder and cheeks, but the peg is doing the work of holding the joint tight.
What wood should the peg be?
Riven white oak, ash, hickory, or black walnut, straight-grained and dry. Avoid dowels because their grain runs along the manufactured length and can contain short grain. The peg should be slightly drier than the frame so it swells after driving.
Why did my peg go in without tightening the joint?
The tenon hole was not offset enough, or it was offset in the wrong direction. Check the direction first: the tenon hole goes toward the shoulder. If the direction is right, increase the offset by 1/32 inch and test on scrap before redrilling the joint.
Can a drawbored joint be taken apart?
Yes, by drilling out the peg and punching the remainder through. Work from the exit side, support the wood around the hole, and use a bit slightly smaller than the peg. Replace the peg with a slightly larger one when the joint goes back together.