Aircraft structures are often engineered with tight tolerances. If a component has a gap or isn’t properly misaligned, the entire structure may succumb to excessive vibrations. Shim washers, however, offer a solution. These specialized washers can fill spaces to meet tolerance requirements.
What Are Shim Washers?
Shim washers are high-precision washers that are used for spacing adjustments. They fill the space between two components. If there’s too much space between the components, you can install one or more shim washers. These otherwise simple fasteners will separate the components so that spacing is no longer an issue.
You can find shim washers in a variety of materials, including the following:
- Stainless steel
- Carbon steel
- Aluminum
- Brass
Shim Washers vs Standard Washers
They may look, but shim washers aren’t the same as standard washers. Standard washers are used primarily for load distribution. They distribute the load of a threaded fastener, such as a bolt, to minimize the risk of damage. Without a standard washer, the threaded fastener’s head will push down against the adjacent part, potentially damaging it. A washer prevents this from happening by spreading the fastener’s load across a larger surface area.
Shim washers typically aren’t used for load distribution. Instead, they are used for spacing. By definition, the word “shim” refers to an object placed between two parts to create space. Shim washers live up to this definition by creating space.
Another difference between shim washers and standard washers is their size. Shim washers are typically smaller. Manufacturers make them in very precise thicknesses, which are often measured in thousandths of an inch.
Shim Washers in Aerospace Engineering
Shim washers are commonly used in aerospace engineering. Airplanes, of course, operate under extreme conditions. Their wings flex, engines vibrate, and landing gear assemblies absorb heavy impact loads. Because of these demanding forces, they must be designed with tight tolerances.
Shim washers offer a practical solution for spacing issues. Rather than machining new components, engineers can use one or more shim washers. The precise thicknesses in which shim washers are made allow engineers to adjust spacing to the necessary tolerances.
While they are used primarily for spacing, shim washers can still help to distribute the fastener loads. The fastener’s load will be spread across the shim washer rather than being focused on the space directly below the head.
In Conclusion
Shim washers provide a simple yet effective way to correct spacing issues. By allowing engineers to fine-tune clearances measured in thousandths of an inch, they help maintain proper alignment throughout the airframe and its systems.
