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, they 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.
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.
Small Joint Assemblies Typically Require:
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.
Acrylic, epoxy and urethane structural adhesives hold over 6.8MPa (1,000psi) in overlap shear strength. Best choice for highest strength, fatigue and environmental resistance especially for metal to metal bonds.
One part solvent-free adhesive that reaches handling strength in 5–10 seconds. Best for small bondlines (<10 cm²). Commonly used on rubbers and plastics. Very tight bondlines are achievable with near instant strength.
These unique adhesives are easy-to-dispense, cure rapidly, and provide effective torque strength while resisting temperature and vibration and sealing out moisture and gasses to protect against corrosion.
All 3M technologies shown below are commonly used in small joint applications. Use the list below 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.