WHITE PAPER Absorbing Centreline and Stack-Up Tolerances with Oval Compression Limiters by Peter Grant - Sales Application Specialist SPIROL Canada Centreline Tolerancing When assembling multiple components with two or more fastening/joining points, there is an increased importance on the location of the Compression Limiters within the plastic component. Compression Limiters must not only align with the mating components, but also maintain a defined centreline tolerance with each other. (Centreline tolerance defines the maximum allowable misalignment between two or more components in an assembly.) This will ensure that the accumulated misalignment remains within acceptable limits so the components maintain their relative positions and can be securely fastened at multiple points within the assembly. Tolerance Stack-Up Tolerance stack-up is the accumulation of multiple individual part tolerances that, summed together, result in the overall tolerance. It is important to understand the cumulative effect on the part production and the assembly process. For example: Will both fastening points align at the minimum and maximum stack up tolerance? Example 1 The Design Engineer of an assembly needed to account for the stack-up centreline tolerances of several fastening points. The requirement of the assembly in Figure 1 was such that there could be no movement up and down along the y-axis. Therefore, the product designer decided to use (1) round Compression Limiter as a datum point, which would be installed first to ensure correct overall positioning. Next, they redesigned the assembly to replace the (3) round Compression Limiters with Oval Compression Limiters to account for any deviations from centreline along the remaining (3) fastening points (Figure 2). Centreline of host component Round Compression Limiter Oval Compression Limiter (1) Round Compression Limiter used as a homing fastening point Host component Plastic component Figure 1 Round Compression Limiters provide precise alignment but do not accommodate stack-up tolerances Figure 2 SPIROL’s Oval Compression Limiters compensate for misalignment by providing an extra 2.25mm of clearance on one axis Oval Compression Limiters A solution to account for stack-up tolerance while maintaining centrelines of the assembly is to use Oval Compression Limiters. SPIROL’s CL400 Split Seam and CL460 Moulded-In Oval Compression Limiters provide 2.25mm of extra clearance on one axis, providing additional flexibility over round Compression Limiters for centreline and stack-up tolerancing. The forming process used to manufacture these oval parts generates little-to-no scrap and allows for high production speeds, resulting in a significantly lower costs compared to machined, cold headed, or powdered metal parts that can have costly unused material (scrap) or slower production output

Strategic Selection of Oval and Round Compression Limiters Innovative Fastening Solutions. Assembly Costs. If the mating component has Lower known tolerance deviations along a certain axis, causing potential misalignment at specific fastening points, Oval Compression Limiters can be used strategically in combination with round Compression Limiters (Figures 2 & 4). This flexibility gives the product designer of the plastic component the ability to provide solutions when alignment challenges present themselves – especially if they do not also have design control of the mating component. Round Compression...