Mechanical Variation Case Study


Mechanics and do-it-yourselfers are always looking for an easier-to-use, more effective tool for the job. Starting with a mechanism concept that has been available for over 70 years, our customer was able to manage mechanical variation using CETOL 6σ in order to perfect the cam-roller design and deliver a zero-degree wrench to the professional and consumer market.

Conventional socket wrenches require 10 to 12 degrees of travel in order to engage the gears. A 12 point box-end wrench requires 30 degrees. The zero-degree design does not have a minimum travel requirement and thus allows for use in very tight spaces. However, one of the main design challenges for this type of wrench is its performance while under load. If the relationship between a cam and roller is not precisely maintained, the wrench will bind if too tight, or slip if too loose.


For this customer, CETOL 6σ is an integral part of the quality management system. CETOL 6σ was applied to the assembly design before tooling designs were finalized. By using the results of the analysis designers identified the critical part features. Identification of critical part features, also known as Critical-to-Quality or Critical-to-Function features, allowed the design team to properly allocate the tolerance budget while considering the manufacturing capabilities of their suppliers.The benefit of this effort was obvious in the first prototype wrenches. Twenty five wrenches were built and each wrench performed as intended. A total of 5 hours was spent on this analysis. This included the time to create and validate the model, interpret results, then communicate results with recommended tolerance settings. A second prototype phase was cancelled, saving the company over  $100,000. Without CETOL 6σ, the customer stated, “It would have been impossible”.

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