Small joints are typically irregularly shaped with only a small area available for bonding. The smaller, more irregular the joint, the greater the challenge to create a firm hold that can withstand heavy wear. Generally these are insertion or overlap joints, or some combination of the two. They are very prominent in sporting goods, electronics, furniture, motors and electrical components.
Mortise and tenon joints rely on the strength of the wood to help resist stress.
Shaft-hosel designs transfer the impact force of a golf club head when striking a ball.
Small joints attached with threaded mechanical fasteners provide stiff, structural assemblies.
Most small joint assemblies are 3-dimensional and are generally insertions such as mortise-and-tenon or tube-in-shaft. Because the joints are small, with forces being applied from multiple directions, the joint receives stress in nearly all forms – tension, compression, shear and cleavage. The insertion design of the joint allows the adhesive to handle the tension, compression and shear stresses while the substrates themselves help handle the cleavage.
Some small joint assemblies are 2-dimensional with a majority of the stress applied as shear or peel/cleavage. Unlike panel-to-frame assemblies which have relatively long lineal lengths to disperse the load, small joint assemblies require very high strength adhesives capable of handling the stresses with very little area.
The 3M technologies shown below are commonly used in small joint applications. Use this list as a relative comparison of product performance.
Most often, if a small joint assembly was previously welded, it will need to be redesigned for adhesive bonding. If a small joint assembly previously relied on mechanical fastening for strength, redesigns are not always needed, and adhesives may be used in conjunction to improve the strength and durability as-is.