Festool Domino and loose tenon joints

A loose (floating) tenon joint has a mortise in both pieces and a separate tenon glued into the two. Festool's Domino joiner cuts those mortises with one plunge each, sized to fit Festool's ready-made Domino tenons, so there is no tenon to cut by hand.

The two machines

Festool gives the DF 500's range as 4 × 20 mm to 10 × 50 mm tenons (thickness × length), and the larger DF 700's as 8 × 40 mm to 14 × 140 mm. The tenon's thickness is also the cutter's diameter: an 8 mm tenon needs the 8 mm cutter. Every size, with inches and the joiner that cuts it, is on the Domino size chart.

Depth and width

Festool's manual says to set the routing depth to half the tenon's length in most cases, so the tenon is centred in the joint. It also describes cutting the first mortise of a joint at the tight width, matching the tenon, and the rest wider so the joint can slide while you line it up: on the DF 500 the width is the cutter plus 13, 19, 23 mm, on the DF 700 the cutter plus13.5 or 16.5 mm. The joint is still exact where the tight mortise is.

Choosing a tenon size

Festool's manual and catalogue list the sizes but give no rule tying tenon thickness to board thickness. The traditional mortise-and-tenon proportion, a tenon about a third as thick as the stock, is a shop tradition rather than a Festool figure, so it is not applied here. The manual's own worked examples follow its depth rule: 5 × 30 mm tenons at 15 mm, 6 × 40 and 8 × 40 mm tenons at 20 mm.

Strength

The USDA Wood Handbook names mortise and tenons among the interlocking joints that make end-to-edge-grain connections strong. It does not test loose tenons as such, and the magazine tests we found each used a different rig, so this site gives no strength numbers for the Domino.