The Technique of FURNITURE MAKING
Gluing and cramping/clamping mitred work
It is a sad truth that mitres never seem to fit so accurately after they have been glued. In theory they should meet exactly, but in most cases positive pressure has to be applied. In applying mitred edgings or mouldings to a panel the two
171 Mitre-marker
ends can be temporarily dry cramped in position, the sides glued and sash-cramped across from underneath, the ends then withdrawn, glued and replaced. Where, however, there is no supporting panel, as in a mirror-frame, etc., other means must be adopted, for any attempt to sash cramp all four sections together usually ends in frustration, for the glue acts as a lubricant and the mitres slide. Picture-framers' corner cramps/clamps are hardly suitable as they are only intended to hold the corners while they are being nailed, and there is no positive pressure to the mitres. Flexible band-cramps are suitable and exert considerable pressure, but they are somewhat expensive, and an excellent substitute is the old corner cramping device of four shaped wood blocks with a straining wire or cord (see p. 144). This can be simply made as needed and will pull the largest frame together provided the cord is strong enough. The wood corner blocks should be waxed or otherwise protected from the glue, and the completed frame laid out on a level base and weighted down at the corners to prevent twist, checking the diagonals of the frame for squareness. It is advisable to size the end grain of the mitres with glue before the final assembly.
Mitre cuts for small breaks
Where the moulding to be mitred is wider than the actual break (172:1) then the points of intersection of the true mitres which halve the overall angle will lie inside the width of the moulding, and small wedge-shaped pieces must be inserted. These in turn will create new overall angles which again must be halved, as shown at 172:1 A.
Mason's mitres
These are a legacy from the stonemason's craft in which simple mouldings or chamfers were worked in the solid, and the mitre return carved as shown in 172:5. A more elaborate form was known as a 'bishop's mitre' (172:6), and both are now only used in reproduction oak-work.
