From the time of the Egyptians down to the present day, hide glue has continued to be the standard adhesive for woodworking. This unqualified acceptance of hide glue merely reflects such inherent qualities as permanence of bond, versatility in use, ease of application, stability under world-wide atmospheric conditions, and economy of use. As a time-tested adhesive for the joining of relatively rigid members such as wood, hide glue commands a unique position in the adhesive field.
In the woodworking field hide glue finds broad acceptance as an adhesive for edge-gluing, assembly, veneering, inlays, finishing, and repairing furniture.
“Edge-gluing” includes such diversified operations as joining together pieces for table tops, chair bottoms, core stock construction, posts and blocks for turning, etc.
Assembly gluing is the putting together of the panels and parts in case goods, cabinets, chair and drawer construction.
Essentially all gluing consists of the application of a thin uniform coating of glue to the properly prepared and dressed surfaces to be joined, lining them up, clamping under pressure until adequate initial joint strength is obtained, then removal for final drying by air under gentle circulation at moderate temperatures until full strength of the adhesive has developed and the stock is at desired moisture equilibrium.
For small assemblies, or for irregular surfaces, or repairing, hand spreading is customarily employed. For production-line gluing, mechanical spreaders such as single or double rod types, perforated plates which rise vertically out of the glue bath for spreading edge surfaces, pressure guns for dowels or lock corner joints, and revolving brushes for dovetail joints are usually employed.
All types of clamps for imparting pressure are in common use, including the common wood clamp, “C” clamp, bar clamp, screw clamp, case clamp and revolving clamp carrier. The purpose of the clamp is to impart uniform, even pressure upon the glued assembly to insure bringing the member surfaces into complete contact, to force air and excess glue from the joint, to promote proper anchorage of the glue within the pore structure of the wood, to maintain the joint in correct position, and to prevent warping. Pressures of from 50 to 200 pounds per square inch are adequate for most conditions. The time under pressure varies with the specific type of assembly. For edge gluing, using a revolving clamp carrier, from 20 minutes to one hour is good commercial practice. Longer periods are required for joints under strain or where incipient warpage may be a factor. Full joint strength is obtained when the glue film has dried to its normal moisture content of 12 percent, which is usually obtained from 12 to 36 hours after removal of the assembly from the clamps.