|Joints between box components||[German version]|
The various components of a wooden box may be joined together in various ways, the commonest being to use nails, screws and bolts.
The following points must be noted when using nails to join components together:
|The quality of the nailed joint is assessed by its „extraction resistance“.|
|The extraction resistance of a nail is increased if its surface is specially coated (e.g. with cement) or treated (e.g. ribbed).|
|Screw nails have much greater extraction resistance than normal wire nails.|
|The head of the nail should always be in the thinner component.|
|The length of the nail must be adequate. The extraction resistance of nails may advantageously be increased by clinching the ends.|
|The nails should have blunt ends to avoid splitting boards, battens etc..|
Screwed and bolted joints
When using wood screws, a pilot hole must first be drilled as the resultant joint is otherwise not sufficiently strong. The pilot hole should be approx. half the screw diameter and approx. 70% of the shaft length. Woodscrews must always be screwed in, never hammered.
For bolted joints, the head should always be on the outside of the box. In order to prevent damage to the bolt and other articles, it is advisable to countersink the bolt head into the lumber. The bolt is best secured inside the box using self-locking nuts which, like the screws, must be provided with washers. In order to ensure the strength of bolted joints, the bolt holes must have no more than 1 mm of play. The size of the bolts to be used is determined by the thickness of the lumber. Up to a lumber thickness of 8 mm, the bolts should be of a minimum diameter of 10 mm, and of at least 12 mm for thicknesses greater than 8 mm.
For boxes having walls consisting of individual boards and not sheets of a large area, the joints between the boards may be as follows:
Figure 1: Butted (butt) joint
Figure 2: Lap joint
Figure 3: Tongue and groove joint
Figure 4: Dovetail joint
The greatest strength is achieved if the boards are provided with a tongue and groove or dovetail joint as such joints have additional strength which reinforces the nailed, screwed and bolted joints. The lap joint increases the strength of the joint on only one side and is thus less effective. The butted joint has absolutely no impact upon strength; in comparison with the other types of joint it withstands far lower loads.