Tolerance in Engineering: How Dimensional Tolerance Impacts Part Production Costs

Created 6 years ago
  • Custom-manufactured components are defined by engineering drawings for consistent production.
  • Drawings define the allowable tolerance of each dimension.
  • Dimensional tolerances should be determined based on how the parts fit together and what the parts are intended to do.

Tools Used to Measure Dimensional Tolerance

How much will a custom-manufactured component ultimately cost to produce? The answer depends on several factors. These unique parts are defined by engineering drawings, which are used by the design engineer to communicate all of a part’s characteristics to the manufacturer so that it can be consistently produced. The drawing contains numerical dimensions that define the size and location of every feature of the part. It also communicates other important attributes, including the material, surface finishes, fabrication methods and other industrial processes necessary to create the part. All of these variables contribute to the bottom line of total overall production cost.

Graph showing costs compared to machining operations for tolerance in engineering

The Importance of Machining Tolerance

Allowable Tolerance vs. Tight Tolerance

Arguably, one of the most important requirements a drawing also defines is the tolerance of each dimension. The tolerance defines the acceptable amount of deviation from the dimension’s nominal value. The “allowable tolerance” window can have a dramatic effect on the manufacturing method and total cost of producing the part. As a general rule, the smaller the allowable deviation, the larger the amount of money it takes to manufacture. This phenomenon is due to the fact that extremely precise dimensions are more difficult to achieve and increase the chance of rejection, rework and scrap.

Also, a “tight tolerance” could require the manufacturer to use much more expensive production methods, machine tools, inspection devices and a significantly greater amount of total processing time. This can add up to a significant amount of money if applied to hundreds of dimensions on the hundreds of custom parts that make up an entire machine. If the machine is duplicated hundreds of times, the cost increases are exponential.

Graph showing approximate relative cost of progressively tighter dimensional tolerances

It is the designer’s responsibility to determine every dimension’s tolerance and make sure that it is contained in the drawing. Dimensional tolerances should be determined based on how the parts fit together and what the parts are intended to do. A designer should ask the question: Will the parts go together and function if I allow a greater amount of variation? If the answer is a definitive “yes,” then a larger tolerance should be allowed. From a cost perspective, dimensional tolerances should be as large as possible without impacting the assembly or the performance of the part.

As a contract manufacturer of sub-assemblies and machines for many of the world’s largest OEMs, Keller Technology Corporation (KTC) can assist customers with dimensional tolerances, the overall manufacturability, and also cost optimization of their designs. These activities can dramatically reduce not only the cost of manufacturing, but also the amount of time it takes to produce the equipment.

More than just a contract manufacturer

Have your equipment designs been optimized for dimensional tolerance? Visit our facilities to see how we can help advance all aspects of your project.

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