Butt joints started it all. When the first two pieces of wood were positioned together and the very first woodworker tried to figure out how to keep them there.
Every joint stems from the need to modify or change this joint to work better for a particular application.
Sometimes it's for speed, sometimes it's for strength, and sometimes it's just to improve the way it looks.
This joint, by itself, is a very weak joint. It almost always has to be modified for strength by adding glue, screws, or some type of hardware to hold it together and make it stronger.
A variety of ways are used to reinforce this basic joint and make it more usable.
A few of the more common methods:
Screws and nails - The modern replacement for the wooden peg.
Wooden Pegs - Pegs were the first joint reinforcement. Still used today in timber framing. It's also used in other applications simply for aesthetic appeal.
Dowels - Just another way to say "wooden peg". These are mostly hidden between the two boards and are very effective for strength and alignment.
Biscuits - A more modern addition. Adding biscuits to the joints help with alignment and also help make glue joints stronger.
Splines - Splines are commonly used along the edge of the boards. Splines hold the surface of the boards in alignment while another fastener, such as nails or glue, is used to hold them in place permanently.
Side Plates - Side plates are used in a variety of ways to hold these joints together. Truss plates for roof trusses, corner plates for small framing, bolt thru plates for timber framing, mending plates when nothing else will work, etc.
Glue - Sometimes glue is all it takes. Glueing boards side by side or surface to surface will make a butt joint stronger than the wood itself.
Pinch Dogs - These little fasteners are driven in the ends of boards, normally to hold the joint together while glue is drying. The shape of the pinch dogs pulls the boards tighter together as it's driven in.
Corrugated Fasteners - These fasteners are used to hold joints together by driving two or more fasteners across the joint. The corrugated shape prevents the joint from pulling apart.
Squaring up a butt joint. . .
Sometimes you may need to square up a joint by hand if you don't have a power saw handy. I just found a great video showing you how to make this job easy whether you're in you're shop or out on the job.