In woodworking or metal fitting, a lap joint
describes a technique for joining two pieces of material by overlapping them. A lap may be a full lap
or half lap
In a full lap, no material is removed from either of the members to be joined, resulting in a joint which is the combined thickness of the two members. In a half lap joint, material is removed from each of the members so that the resulting joint is the thickness of the thickest member. Most commonly in half lap joints, the members are of the same thickness and half the thickness of each is removed.
The full lap is a very basic method of joining two members and requires little or no joinery skills to make. It requires some form of mechanical fastener
to be effective. It offers no resistance to racking but some resistance to twisting and shearing
depending upon the fastener used.
Large framing members in light frame construction are often joined by lapping - for example bearers supporting joists.
- Bracing where bracing members overlap
- Temporary framing
- Some applications in timber frame construction
Half lap joints are used extensively in construction and cabinetry for framing. They are quick and easy to make and provide reasonable strength through good long grain to long grain gluing surface. The shoulders provide some resistance to racking. They may be reinforced with dowels or mechanical fasteners to resist twisting.
- Frame assembly in cabinet making - particularly when frame members are to be shaped after joining.
Half lap joints can be cut by the following methods:
There are four basic types of half lap joint:
Also known simply as a Half lap
, it is the basic form of the lap joint and is used when joining members end to end either parallel or at right angles. When the joint forms a corner, as in a rectangular frame, the joint is often called a corner lap
. This is the most common form of end lap and is used most in framing.
For a half lap in which the members are parallel, the joint may be known as a half lap splice. This is a splice joint and is an alternative to scarfing when joining shorter members end to end.
Both members in an end lap have one shoulder and one cheek each.
- Internal cabinet frames
- Visible frames when the frame members are to be shaped
This form of the half lap is used when one member crosses the other. The main difference between this and the basic half lap is that the joint occurs in the middle of one or both members, rather than at the end. The two members are at right angles to each other and one member may terminate at the joint, or it may carry on beyond it. When one of the members terminates at the joint, it is often referred to as a Tee lap
or middle lap
. In a cross lap where both members continue beyond the joint, each member has two shoulders and one cheek. For a Tee lap, one of the members has only one shoulder.
- Internal cabinet frames
- Simple framing and bracing
This is a Tee lap in which the housing has been cut at an angle which resists withdrawal of the stem from the cross-piece.
- Framing applications where tension forces could pull the joint apart
Mitred half lap
This is a variation of the end lap which shows a mitre
on the face of the finished work.
The mitred half lap is the weakest version of the joint because of the reduced gluing surface.
- Visible framing applications where a mitred corner is desired