One of the least understood facets of spring design is specifying the proper tolerance to various dimensions of the spring. Sometimes the person engineering and/or drafting a new spring will disregard specifying any tolerance because they are unfamiliar with proper spring tolerances or they may feel that the block tolerances on their standard prints is adequate. More often than not, however, block tolerances apply to machining, molding or casting processes and are far different from the needed tolerances for coiling and stamping spring materials.
Every design is different, and the needed tolerances are highly dependent on materials and the equipment used to make the spring. Physical characteristics, including the number of coils, the spring index (Mean Diameter/Wire Size), the free length and forming operations required to complete the spring, all affect normal variation in the process of forming springs. Special processes are required to reduce this normal variation and add cost.
The best way to save cost on any new design is to identify the critical requirements of fit and function (loads and/or rate) and to work with the spring manufacturer to design the best spring possible while considering process capabilities and standard spring tolerances. By doing this, special processes can often be eliminated or at a minimum be reduced.
Please contact the Newcomb Spring facility nearest you for more information on the considerations of spring design.
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