Joining wood 1: screws, nails, glues and knock-downs

There are many different ways of making joints in wood. The method used will depend on the function of the product, the strength required and the quality of the product. Temporary fixings will often be done using fastening components such screws or bolts. More permanent joints can be achieved with glue, or with nails - though these may lack strength and be rough-and-ready in appearance.

Screws

All screwing needs two sizes of hole. The clearance hole must be very slightly bigger than the shank [shank: smooth, narrow part between the head and core of a screw ] of the screw, so that the shank can move freely in the clearance hole. The pilot hole must be smaller - slightly smaller than the corecore: The core is the innermost part of the Earth. of the screw - so that the core fits tightly into it.

Screws come with different types of head. They can be flat or round-headed, and be fitted with a slot (for traditional screwdrivers), crosses (for Phillips or Posidrive screwdrivers) or square holes (for square drivers). If the screw head is to lie flush with the surface of the wood, the hole must be enlarged or countersunk.

Self-tapping screws are made from very hard steel. They have a thread which goes all the way up to the head, and cut an internal thread as they are screwed in. They can be used in metal and plastic as well as wood. Machine screws are used for joining metal and plastic components.

Screw types

Nails

Nails come in different shapes and sizes. Nails are much cheaper than screws and quick to put in. You do not need to drill holes in the wood first, except sometimes when using hard wood or to prevent the wood splitting.

Glues

When using wood glue, make sure you:

• Get the surfaces to be glued to fit well - no gaps!
• Don't put any finish on the surfaces to be glued.
• Make sure the surfaces are clean.
• Get everything ready before you start - glue, brush, damp cloth, clamps and blocks to protect your work.
• Don't start to glue up unless you are sure you have enough time - you can't stop half way through!

Knock-down joints

Knock-down joint

Much furniture is sold in flat packs. This makes it easy to transport and store. The customer then has to assemble it at home. Usually knock-down (KD) fittings are used. Most KD fittings consist of corner blocks or bloc-joint fittings. Usually these are made from a plastic such as nylon.