shimming

A shim is a thin, often wedge-shaped piece of material inserted between two parts to fill gaps, achieve a precise fit, adjust alignment, or provide support. Shims compensate for irregularities in interfaces, accommodate expansion or contraction, and aid leveling in assemblies or installations.

Shims come in various forms, including flat metal plates, laminated or stacked shims, and wedge-shaped shims for gradual lifting. Common materials include steel and stainless steel for strength and durability, aluminum for light weight, plastics such as nylon or polycarbonate for electrical insulation or corrosion resistance, and wood or composite materials for carpentry applications.

Sizes range from fractions of a millimeter or thousandths of an inch to several millimeters in thickness, often stocked in standard increments to allow precise adjustment. Laminated shims are built from thin sheets that can be stacked to achieve a target thickness. Precision shims, including shim packs, are used in machine setup and alignment.

Typical uses include leveling machinery, aligning turbines, engines, and furniture, squaring cabinets, adjusting window or door gaps, and spacing parts during assembly. Installation involves cleaning mating surfaces, selecting an appropriate material and thickness, inserting the shim to create even contact, and re-tensioning fasteners gradually to the required torque. Avoid using a single thick shim or hammering; replace with smaller additions as needed.

Shims are chosen based on load, temperature, corrosion resistance, and material compatibility. Improper shimming can lead to loosening, uneven load, or premature wear. Maintenance includes inspecting for deformation, corrosion, or cracks and replacing compromised shims.