The biggest difference between a stock spring and a custom spring is that of tolerance. Tolerances set the benchmark for both the performance and profile of the spring as well as how identical each spring is when repeated in manufacturing. It sets a guideline that each spring must maintain.
Stock springs are made using standard tolerances because one spring may be used for a variety of general-purpose applications. Custom springs are designed to a higher standard and tighter tolerances and provide a better solution for critical applications where safety, performance or durability are essential the part or component working to spec.
Critical applications include parts and components that are essential and absolute for the product to function correctly. This includes applications that if they fail may cause damage, safety or death to users or cause irreputable damage to the product or machine. Stock springs are a good example of non-critical applications, they have a wide (or low) tolerance and thus are not precise. These types of springs are great for non-essential functions like doors, panels, or applications that do not require a specific set of spring requirements.
Springs for critical applications are custom designed springs that have a high precision and tighter tolerances because the optimum performance of the application require a precision tolerance spring. These custom springs made be used in something as complicated as an aviation landing gear or flaps or medical devices and power generation. Click here to see some of the solutions be provided with custom springs.
A precision spring or high tolerance spring is a part that is very exact when it comes to its performance characteristics. This is done because the spring becomes and integral part of the application’s success whether it be performance, durability or safety. A stock spring is not as specific and may shift or cause wear and damage or time because it was not specifically designed for the application. For general purpose applications this may be fine because the demands upon the spring are not strong and some leeway is available. But when the application is demanding a custom spring may be necessary because it will not shift, bend, because of the higher tolerance of the spring when it was designed and manufactured.