Floating Tenon Size for Garden Bench

[Adel Heiba]

I am interested in building an outdoor garden bench with floating tenons. I am curious as to the appropriate size of the tenons. I have access to a slot mortiser with bits of either .6” or .8”. Standard recipes with similarly sized lumber call for 3/4” conventional tenons. I would appreciate any advice

[John TenEyck]

Hand chopped mortises traditionally are 1/3 the thickness of the workpiece, so 1/4" for something 3/4" thick. With a mortiser, however, the mortise can be thicker because there's little danger of blowing out the sidewall like there is chopping them by hand. I use 3/8" thick floating tenons in 3/4" stock, which is half the thickness. With that logic, it would be appropriate to use 0.6" tenons in stock at least 1-1/4" thick, and 0.8 tenons in stock at least about 1-5/8" thick. For even thicker stock, two thinner tenons often are used, spaced across the thickness of the workpiece.

Tenon length is typically at least 3X the thickness, and longer still for exterior applications. I've never thought I needed more than 2" though for garden furniture.

John