Technical Data for Mortise and Tenon Joints

compiled by Bill Tindall

The data presented below are from a publication by Hill and Eckelman, Flexibility and Bending Strength of Mortise and Tenon Joints, Furniture Design, December, 1973.

The strength of a mortise and tenon joint depends on the length and width of the tenon, the adhesive used for assembly, the tightness of fit and the shear strength of the wood.

As tenon length increases joint strength increases proportionally.

Tenon Length	Relative Strength
0.5"		.48
0.75		.80
1.0		1.0
1.25		1.12
1.5		1.28
1.75		1.46
2.00		1.66

Tenon Width	Strength, in-lbs
0.5"		2000
1.0		2500
1.5		2800
2.0		3600
2.5		4000
3.0		4600

Similarly, a wider tenon yields a stronger joint.

(These width data are for hard maple, 3" rail width, 1" tenon length, phenol-resorcinol adhesive.)

The strength of the joint depends on the adhesive used.

Adhesive	Relative Strength
phenol-resorcinol	1.00
hide glue	1.05
Urea formaldehyde	1.24
PVA (yellow glue)	1.32

Gap		Relative Strength
0.000–0.002"		1.00 (need to tap together)
0.003–0.005		0.94 (snug fit)
0.006–0.008		0.89 (this is a very sloppy joint)

A better fit results in a stronger joint. Gap is defined as the difference between the tenon thickness and the mortise thickness.

Wood with a higher shear strength results in a stronger joint. The shear strength of poplar, walnut, red oak and hard maple are 1400, 1600, 2000 and 2700 psi, respectively.