Fixed and Floating Fastener Variation
Raytheon Systems Company
Chris Cuba began his career at Texas Instruments in 1984 and has been a key contributor on several
defense programs as a systems producibility engineer. During this time, he has developed expertise in
mechanical assembly producibility, mechanical tolerancing, and product design-to-cost. He was soft-
ware development manager and applications engineer for the mechanical tolerancing tool CE/TOL.
Mr. Cuba currently works as a member of the Mechanical Tolerancing and Performance Sigma Team at
Raytheon Systems Company. As a Six Sigma Black Belt, his responsibilities include dimensional man-
agement consulting, Six Sigma mechanical tolerance analysis and allocation, and mechanical
tolerancing training. He graduated from Oklahoma State University with a bachelor’s degree in me-
This chapter describes an approach to understanding the inherent assembly shift and manufacturing
variation contributors within a fastened interface. In most cases, the fastened interface must meet two
requirements: The parts must fit together and provide minimal assembly variation, and the variation
allowed from the fastened interface should relate to a product performance requirement.
In this chapter, each variable of the fastened interface is broken down to understand its contribution
to the total assembly variation.
• First, the chapter shows a worst case tolerance study on features of size that are located using a
position feature control frame to understand the virtual and resultant condition boundaries.
• Next, features of size are used in an assembly to understand variation within a fixed and floating
23-2 Chapter Twenty-three
Fig. 23-1 shows an example dimensioned using a position feature control frame to locate the hole. The
feature control frame locates the hole using the maximum material condition (MMC) modifier. When using
the MMC modifier, tolerance may be added