Fig. 51. The Hand Screw
Glue is of two kinds, fish and animal. Both are made from refuse matter,—animal glue being manufactured from such products as bone, horn, hoofs, and hide.
The dry glue in the form of chips must be dissolved in water and heated, being applied while hot. Liquid glues sold in cans ready for use are now very common and require no heating.
In making a glued joint it is usually necessary to hold the pieces tightly together until the glue has set, or hardened, and as this takes some time, hand screws built on the principle of the vise are resorted to. [Fig. 52] shows two pieces glued together and fastened in a pair of hand screws. Care must always be taken to keep the jaws of the latter parallel. At a this is shown done properly, while at b is shown a careless method which, of course, will spoil the joint.
Fig. 52. Method of using the Hand Screw
In gluing on the end grain a preliminary, or sizing, coat of glue must first be made to fill up the pores, which act very much like a sponge. This coat should be allowed to dry, or partially dry, before applying the final coat; otherwise the pieces will be held weakly, if at all. Beginners are inclined to use too large a quantity, and this tendency should be avoided.
In some cases nails are used together with the glue, as at the corners of picture frames. It is customary in this instance to nail in only one direction, as shown in [Fig. 53].