I’ve been asked before on how to decide what joint you’re going to use in a woodworking project.  While there is no hard and fast formula to follow, the question does merit discussion.  There are a lot of factors that go into deciding what joint is best suited for the project at hand.  Some areas to focus or discuss are structural integrity, ease of manufacture, showmanship, and to a lesser extent, what machinery or tooling is needed to make the joint.  Also, the material itself may decide the type of joint best suited for the project.

If I’m building a project that will have a load bearing member, such as a shelf in a bookcase, I’ll try to use a dado.  A dado supports both ends of the shelf very well, and when done right, makes a nice workmanship type of appearance.  I’ll typically use a dado joint when I’m working with plywood to span a larger distance.  I’ll also make a dado on the four sides of a drawer box to accept a ¼” thick piece of ply as the bottom of the box.  Dadoes are easy to cut with a dado stack on the table saw, or  the right sized bit in a router.  They are very difficult and time consuming to cut by hand.

Mortise and tenon joints are pretty similar, if you think of the tenon being fitted into a stopped or short dado (the mortise).  There is a lot of mechanical rigidity and glue surface area, making a strong joint.  If you align the tenon so that its grain runs in the same direction as the mortised element grain, you can achieve a joint that is essentially immune to wood movement.  If the tenon grain is perpendicular or across the grain of the mortised bit of lumber, you may get some splitting in the mortised element due to the movement of the tenon.

A bridle joint is similar to a mortise and tenon joint, but differs in that the tenon is the entire width of the member, and the mortise is at the end of its piece of wood.  This creates the maximum amount of glue surface area.  Bridle joints are typically found in the corners of cabinet doors, where the rails and stiles intersect.  

Yet another type of mortise and tenon joint is dowel construction.  Mating stopped holes are drilled in the two pieces to be joined, and a dowel is inserted and glued into place.  I use this joint alot when I’m joining a table apron to the table legs, or when I’m edge joining two pieces of lumber together to get a wider piece of lumber.

Dovetails and all of the family variants (sort of like the weird uncle everyone has) such as half-blind, mitered half blind, japanese sunburst, box joints, etc, are both beautiful (to me), mechanically strong, can be cut exclusively with hand tools, and resist the movement of wood, as the grain runs in the same direction between the two joined pieces.  They are general considered the epitome of fine woodworking as they take considerable skill to layout, cut, and chop the joint to fit.  The tools needed to make a dovetail joint are a marking gauge, handsaw, mallet, and chisels.  It also helps to have a sliding bevel gauge, but isn’t necessary.  There is an entire cottage industry around making jigs for cutting dovetails using a router, but I don’t have one.  The one time I did use a router dovetailing jig I found it very finicky to set up and use.  If I was making a hundred drawer boxes at one time I would set up a router jig and knock them out in industrial fashion.  If I’m only building one box, such as a tool box or jewelry box, I can knock out the tails and pins by hand in about the same time it takes to set up a jig, adjust the router, and do it by machine.

I want to touch on Kreg jigs and joinery for a moment.  Very simple to use, all you need is the jig and a screw gun.  It makes a very strong and sturdy joint, in both solid wood and plywood.  The downside is that it only really can be used for 90 degree joints (you can do it with off-90 degree joints, but you have to mess around with the pocket hole placement), and you have to put the pocket holes in the hidden/non-visible part of the joint.  If the joint is going to be exposed on all sides, like say attaching a drawer front to the drawer box, I suggest using a different type of joint.

There is no hard and fast rule for deciding which joint to use in an application; I hope I’ve given you the Reader some sort of general rules of thumb to consider when selecting a joint for your application.