Learning Unit 2 Construct widening joints

Widening Joints are used to make wider boards by joining narrower one edge to edge. Whichever jointing method is chosen, care should be taken to ensure the curve of the Annular Rings is reversed on adjacent boards as shown.

As timber dries out, its Annular Rings will tend to try and straighten. Reversing their direction in this way minimises the degree to which the widened board will cup or warp.

Note: Although now almost universally replaced by MDF, solid timber window sills would be positioned 'heart side up'. This ensures that if there is any movement as the Annular Rings tend to straighten, the sill would 'bow' upwards in the centre rather than 'cup' and hold moisture.

To avoid this problem almost completely, choose boards which have been sliced radially from across the centre of the tree, and whose Annular Rings are therefore close to being at right angles to each face (these boards are known as Quarter Sawn and Rift Sawn - they are much sought-after and will be hard to find!)

It is important to ensure joining surfaces are straight and square and to arrange boards such that their Grain goes in the same direction - this is so any subsequent planing and finishing is made easier. Check for Squareness by balancing one board on top of another and testing with a straight edge.

Some planing will be needed after jointing to ensure the finished boards surfaces are flat, so choose boards somewhat thicker than the required finished size to start with.

This unit has the following learning objectives:

• LO 2.1 Identify types of widening joints
• LO 2.2 – Construct widening joints
• LO 2.3 – Assemble parts of widening joints