Clamping mitre joints
Gluing the Joints.—If the corners are unusually well fitted, a good joint can be made by first sizing the ends with glue and then firmly pressing the pieces together upon a true surface, leaving them undisturbed for four or five hours until the glue is hard. By sizing the ends of the joints is meant thoroughly filling the end pores with glue, rubbing it into the pores with another block. Generally speaking, however, it is necessary to make use of a mitre-clamping device. If a special clamping device is not available, one can be easily made by gluing small soft wood blocks to the parts of the frame near the corners, as shown in the accompanying drawing. In a half hour or so these blocks will become firmly set so that the mitre joints may be glued together, clamping them up with a hand screw. As already explained under the general directions on gluing, it is good practice for a beginner to glue up opposite corners and not attempt to glue up the two remaining corners until the first two are well set. When the first two corners are well set they should be nailed; and before the two remaining corners are glued it is well to try the parts together to see if they do not require a little correcting before gluing. These joints also should have light nailing after the glue has been set. In nailing, small holes should be made with a brad awl or drill in order to avoid splitting the corners, and long finishing nails should be used.
The Defect of Shrinking.—With proper tools the mitre joint is the easiest one to make, but it has one unavoidable defect, especially in wide frames. It is very difficult to get stock well seasoned and almost impossible to get it perfectly seasoned, so that wide frames, however well finished, must be expected to shrink a little after they are joined together. As most of this shrinking is across the width of the stock it is evident that it will tend to open the mitre joints on the inside of the corners. This is what happens almost invariably with joints made in this way from wide stock in picture framing. The same defect is also frequently observed in the interior finishing around windows and doors.
Halved lap joint
There are three other methods of joining the corners of picture frames—viz., the halved lap joint, the mortise and tenon joint, and the dowelled joint. A drawing is shown to illustrate these three kinds of corner joints, and it is hardly necessary to say that no one of them is open to the same objection that attaches to the mitre joint. All these joints require accurate cutting and rather more of it than the mitre joint requires, but they are more easily glued up. The halved lap joint is easily clamped up with a common hand screw, even when the frame is a very large one. But the other two require long clamps in order to pull the joints up well.
Mortise and tenon joint
