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General notes on assembling framing joints
General notes on assembling framing joints
All framing joints should fit accurately together hand tight without undue forcing, which may split the timber. Test by assembling them dry before gluing up.
Housed, halved, notched, mitred and rebated joints may be nailed or screwed as well as glued. Bridle joints may be dowel pinned, and mortise and tenon joints dowel pinned and wedged. Other joints should be glued only.
Any type of glue is suitable except for exterior work, where waterproof glue is required. A little glue should squeeze from the joint when pressure is applied: wipe it off with a wet cloth before it sets. Do not allow glue to set in brushes.
End grain, which is more absorbent, should be given a preliminary coating of adhesive and then recoated when other parts have been glued. A small spatula-shaped piece of wood is useful for gluing dovetail sockets.
Sash cramps are used to bring shoulders of joints tightly together. Cramps should be parallel and square. Test the frame for squareness by measuring the internal diagonals with a thin rod (Fig. 1). If out of square, a sharp tap on the end of the stile at the long diagonal corner or moving the end of one or both cramps towards that corner should produce the desired result (Fig. 2).
Wedging of mortise and tenon joints is done after the frame is cramped. Preferably, two people should work on this so that wedges can be driven in pairs, the outside wedges being inserted first. Do not forget to glue the wedges.
Wedged frames can be removed from cramps without bracing before the glue sets. Other frames may require a light brace across the corner to keep them square. Dovetail joints should not need cramping, but may require bracing. Never attempt to flush plane any joint before the glue has set.
On joints that have an exposed end grain (i.e. finger/comb, halving, through mortise and tenon, and bridle), when setting out the joint, allocate an extra 1 mm on exposed parts. This allows for flushing off with a smoothing plane after.
Mitre joints can be cramped with a G cramp if tapered blocks with paper separators are temporarily glued to the work (24 hours drying time) to provide parallel surfaces (Fig. 3).
Figure 1. Diagonal stick compares distances AD and BC. To square frame, cramps are adjusted until diagonals are equal
Figure 2. Cramps are adjusted to pull frame square
Figure 3. Blocks glued to edges of joint with paper separators permit use of G clamp
Outline a method for checking a rectangular table frame for squareness without using a right angle square.
Use a tape measure to check diagonals across frame. When measurements are the same, it is square, as long as opposing sides are equal
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