Sunday, January 20, 2008

Woodworking Joints - Key to DIY Furniture Projects

It's no secret in woodworking circles that strong wood joints are critical with DIY furniture projects. This is true with new furniture or when restoring older furniture pieces. It's also important in other areas of woodworking. Just as the saying goes, "A chain is only as strong as its weakest link", the same is true in woodworking.

Types of Wood Joinery

One school of thought is that there are two broad categories of joints - those using wood glue and those that don't. Japanese wood joinery, for example, is known for its tight, intricate, and glueless joints. There is a whole family of hand saws for cutting them. Other glueless applications are the ones of old, where a mortise was cut all the way through wood and the tenon extended through the other side far enough to accept a keeper peg.

Glued-up joints, on the other hand, are used almost exclusively today, so that's what I'll ramble on about here. When using glue, it's important to choose the right type of woodworking glue for your project.

The Box Joint

A Box joint is also known as a finger joint. The term finger joint is descriptive: the corner is formed by interlinked, square "fingers". The term "box joint" is historical. Before cardboard was so prevalent, produce was brought to the market in wooden boxes.

The challenge was making the box corners hold together as it got slammed about. Enter the box joint. Why? Because cutting box joints is easy to do on a mass market scale using a jig on a table saw. It was very economical.

The Dovetail Joint

A dovetail joint is made with interlinked corners like the box joint. It gains its incredible strength because of its mating surfaces. The "pins" are flared like a dove's tail, and fit neatly into the corresponding "socket". At the top and bottom are the "shoulders". Dovetail joints are ideal for applications that get a lot of action, such as drawers.

How do you cut a dovetail joint? The traditional way is with a dovetail saw (pictured above). But to get the most accurate and professional looking results, it's best to use a jig and a special dovetail router bit.

Other Woodworking Joints

Now, this would be a long list, but blogs aren't textbooks, so here are some popular ones:
  • The Lap Joint - The two pieces of wood are cut to overlap. It is used on things such as cabinets or sideboards.
  • Tongue and Groove Joint - A tongue is cut on one piece of wood, centered on the stock. A corresponding groove is cut on the other piece to receive the tongue. It's used to make wider panels, doors, or when installing hardwood floors.
  • Dowel Joints - A hole is drilled through the two pieces of wood and a glued-up dowel is inserted. Sometimes used to strengthen other joints, like the lap joint.
  • Biscuit Joints - Using a biscuit cutter, a half oval is cut into the center of two pieces of wood. Then a full oval glued-up wood biscuit is inserted and the two pieces are joined. It's a great way to form wider panels or build a butcher block countertop.

Obvious Notes - Always use wood clamps with glue joints and put wax paper under your project to keep it from sticking to your workbench!

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