Engineering tolerance is the amount of variation in a product that will still allow it to function as intended. Some products have very high tolerances; a shovel, for example, will work very well with blades of a variety of widths. Others do not have this flexibility and must be produced precisely to ensure they will work right. This is a particular concern with articulating moving parts in components like aircraft engines.
In the process of developing plans for a product, engineers create certain specifications, which include the amount of variation that will be acceptable. They consider how and where the product will be used, and what kinds of conditions might be present. Their detailed discussions of what the product will do and how also provide information about how close the tolerances need to be. On engineering drawings used in product development, engineering tolerance can be indicated. This is important for developing manufacturing processes to meet the needs of the product.
Examples of this principle can be seen in everyday life. Something like a refrigerator, for example, must be able to make a tight seal to keep the objects inside cool. The rubber gasket used to create the seal leaves some room for error, but significant deviations in the refrigerator door would make it impossible for the gasket to compensate. An engineering tolerance can include any measurable properties of a device, including width, depth, and length.
During the development phase, engineers can discuss how to meet the specifications of the design. This might include the use of precision equipment that can cut, weld, and perform other tasks within a very narrow range. The engineering tolerance can also be used to develop quality specifications. Companies use these to determine which products pass muster and can be released, and which must be discarded. Quality control officers can measure and check products as they come off the line to confirm that they adhere to the standard.
This is a special concern whenever an engineering tolerance pertains to safety matters. Engineers typically want to err on the side of caution when it comes to safety recommendations. In the development of safety-related recommendations, engineers can consider the worst case scenario, an unlikely series of events that could lead to injury if a product was not designed well. The engineering tolerance for products like heat-resistant tiles used in fireproofing and moving parts used in safety equipment is typically very precise.