The Technique of FURNITURE MAKING

Mortise and tenon joints

These are probably the best known of all wood­working joints. The variations are many and only the principles and the main types need be given.

Mortise and tenon joints are usually referred to as wedged through (142:1) and stub or blind (142:2). The former is more applicable to joiners' work where the end grain of the tenon shows on the edge of the stile and is painted over, but as it has decorative possibilities it is included. The familiar type for furniture is the stub tenon with or without haunching (142:3) whose function it is to keep the unsupported part of the rail from twisting on the face.

All tenoned work follows the same general principles. The width of the mortises is slightly over one-third the thickness of the stile (142:5) but pitched according to the width of the hand - or power-chisel available. The rail width in corner mortising is also divided into three, one - third for the haunch or seating and two-thirds for the tenon, less a bare 1/16 in (1.5 mm) shoulder at the bottom edge to cover any slight gap caused by a slack tenon or bruising of the mortise socket end in levering out the waste in hand-methods. The final width of the tenon itself less the haunch becomes the length of the mortise cut to receive it. In all framed-up work it is always better to provide an extra length to the stiles to form a horn (142:1) at top and bottom which helps to prevent the splitting of soft wood while deeply mortising, and also to protect the corners from incidental damage. These horns are left on until the door is fitted.

Where the stiles and rails are grooved or rebated/rabbeted for panels the mortises are pitched to coincide with their position; they can be wider but not narrower than any groove or rebate in the rail. The mortise depth should be slightly more than the length of the tenon so that a small gap is left for surplus glue, while plenty of wood substance should be left between the bottom of the mortise and the outer edge of the stile, certainly not less than3/16 in (5 mm) even for a small door.

HAUNCHES

Grooved frameworks will require haunches to. fill them; if there is no groove a secret haunch (142:4) can be fitted; although light doors may not require haunching and the modern tendency is to omit them if possible.

LAYING OUT, ETC

Cutting lists usually take the gross length of the rails right across the width of the frame irrespec­tive of the type of tenon. Laying out can be done entirely by measurement, but in practice it is better to mark the stiles clearly with top marks left' and 'right', and face marks uppermost on the inside or panel edge, and place them on the bench-top in the finished position, allowing an extra 1/8 in (3 mm) on the overall width for cleaning off and fitting. The rails are then marked and placed over the stiles also in the correct position, and allowing 1/8 in (3 mm) extra on the height. The critical positions of the rail shoulders, i. e. the net panel opening width, are then ticked, and also the opening height on the stiles. The stiles are then hand-cramped/ clamped together and all the measurements— actual height of door frame (plus 1/8 in [3 mm] extra), depth of haunch or seating, position of mortise allowing for any groove or rebate in the rails—squared across and the rails similarly treated for shoulder length (width of panel opening) and length of tenon. The actual width of the tenon and the depth of the haunch can be decided later after the mortise has been cut. The mortise-gauge is then set for the width of the mortise and gauged from the face sides on both stiles and rails, after which the mortises can be chiselled, first boring out a series of vertical holes to save labour. When completed the tenons can be sawn in with the cuts always on the waste side of the marks. Figures 143 and 144 show the rail canted over first for one cut and then for the other, with the rail uprighted for the final cut. The shoulder-lines are marked with a knife and sawn through, and the tenons offered

against the mortise for their final width and position of haunch. (Figure 145 also shows use of bench-hook for sawing shoulders, small parts, etc.)