Admittedly, my previous post was a bit harsh. Without any remorse and sans even one iota of apology to the douchenozzles in question, I concede that things got a little out of hand on Friday.
I like to keep it pretty highbrow around here, so let’s talk about one of my favorite joints: the cross-lap joint.
The cross-lap joint is all about precision. In its simplest form, two pieces are joined to form an overlapping “T” through two dadoes. Each dado must be precisely sized to snugly fit the mating piece and (usually) the combined depth of both dadoes is equal to the thickness of one of the pieces. This precision is achieved, first and foremost, through careful layout.
For me, the most accurate way to mark each dado is to scribe an initial line with a marking knife and, leaving the square in place, use the mating piece to transfer the dado width. I tend to mark my dadoes about 1/64″ narrower than the mating piece when working in softer woods. In harder woods, it might be only a few thousands of an inch. I then transfer the width lines to the sides and scribe my depth line normally.
Unless the boards are wide (6″ or more), I will use a tenon saw to establish the outside walls and then chisel out the waste to just above my depth line with stabbing motions. On twider boards (or in the case of stopped dadoes), I may only establish the show faces of the walls with a saw and the do the rest by chisel.
I always wear safety glasses when paring in this orientation.
After test fitting for snugness (and paring down the walls to the scribe lines, as necessary), I then fine-tune the dado depth with a router plane, taking very shallow passes until I hit my scribed depth line. Rinse and repeat for the other dado, fine tuning dado depth to ensure the pieces are joined flush.
When done right, and used in the correct orientation, a cross-lap joint can have mechanical strength and may require little reinforcement.
The first dado in process.
The cross-lapped pieces above are the base of a small plant stand. Assuming I accurately locate the through-mortises on each of the legs to evenly distribute the vertical load, the cross-lap joint won’t require any reinforcement. Assuming.