Through Tenons Done Right: Layout, Cutting, and Clean Shoulders

Through tenons announce themselves. Unlike their hidden counterparts, they extend completely through the mortised piece, showing end grain on the opposite face. When executed perfectly, they demonstrate mastery. When botched, they advertise inexperience. There’s no hiding your work here.

Why Through Tenons

Beyond aesthetics, through tenons offer practical advantages. You can see that the tenon actually reaches full depth. You can wedge the tenon from the exposed end, creating mechanical lock that doesn’t rely on glue. And you can replace the tenon piece if it ever breaks, since the joint can be driven apart.

Traditional furniture often used through tenons on stretchers and structural members where maximum strength mattered more than visual sleekness. Arts and Crafts furniture celebrates the joinery, making through tenons a design feature.

Layout Precision

The mortise width should equal one-third of the mortised piece thickness. This provides adequate cheek strength while maintaining a substantial tenon. Narrower tenons weaken the joint; wider ones leave fragile mortise walls.

Mark the tenon length from the actual mortised piece, not from a measurement. Wood thickness varies, and you want the tenon to project a consistent amount regardless of any variation in your stock.

Use a marking gauge for all parallel lines. Set it once and mark all related pieces to ensure consistency. A knife line beats a pencil line for precision because it creates a physical registration point for your saw.

Cutting Clean Shoulders

The shoulder tells the story. Gaps at the shoulder scream poor workmanship louder than any other flaw. Start by establishing a deep knife line all around the shoulder position. This severs the surface fibers and prevents tearout.

Create a small V-groove on the waste side of your knife line by paring toward it with a chisel. This groove guides your saw, preventing it from wandering onto the show surface. Saw carefully against the knife wall, letting the groove keep you honest.

For hand sawing, use a fine-toothed backsaw and let the weight of the saw do the cutting. Forcing the saw causes it to wander. Saw all four shoulders before touching the cheeks.

Cheek Cuts

The tenon cheeks require dead-flat surfaces. Any hollow or hump reduces glue surface and creates gaps. On the table saw, use a tenoning jig that holds the workpiece vertically. Make the cut in a single pass if possible.

By hand, establish the cheek cuts with a rip saw, splitting the waste from the tenon. Stay well off your line initially. Pare to final dimension with a wide chisel or shoulder plane, checking flatness with a reliable straight edge.

Mortise Execution

A through mortise must be clean on both faces. The entry side gets cut normally, but the exit side needs protection from blowout. Drill or chop halfway through from each face, meeting in the middle.

Mark identical layouts on both faces using the same gauge settings. Any misalignment between faces creates a twisted mortise that won’t accept a straight tenon. Check alignment frequently as you work.

Final Fitting

Pare the tenon cheeks incrementally until the joint goes together with hand pressure. Driving a too-tight through tenon risks splitting the mortised piece because there’s nowhere for the wood to flex.

The tenon should project 1/16 to 1/8 inch beyond the mortised piece face. After glue cures, plane this flush or leave it slightly proud as a design element. Either approach is historically correct.

Sand or plane the exposed end grain after the joint is assembled and cured. This ensures a perfectly flush surface that accepts finish evenly. Through tenons done right become the focal point of any piece they grace.