# Statistical Tolerance Analysis--A Survey on Awareness, Use and Need in German Industry
## 5 Awareness of Deviations and Tolerances  
The fundamental assumption of all the following discussions is that the interviewees were familiar with tolerances and had a basic understanding of tolerance engineering. Therefore, we first evaluated to what extent participants already dealt with deviations and tolerances in their daily work routine and underlying development processes. In general, the overwhelming majority of the respondents (\(\sim\)94.1% = 96 of 102) dealt with deviations and tolerances and their effects on the functionality and aesthetic quality of products. Thus, the results of this survey are based on sound feedback and thus allow conclusions and recommendations with generality. Almost all participants (94 of 102) asserted that tolerances were specified and detailed in drawings and/or 3D-CAD models of their products' components and assemblies. In Germany, the tolerances in orientation, location, profile and run-out are classified to so-called \"Lagotelaranzen\" [57]. Hence, this term was used in the questionnaire. These tolerance specifications include:  
* Dimensional tolerances in size by \(\sim\)97.9% (=94 of 96);
* Form tolerances by \(\sim\)87.5% (=84 of 96);
* Tolerances in orientation, location, run-out and profile by \(\sim\)83.3% (=80 of 96);
* Surface roughness by \(\sim\)69.8% (=67 of 96). At first glance, this response is surprisingly positive and suggests an already existing broad knowledge of tolerancing practice and existing standards. However, in most cases, these tolerances were assigned relying on the engineer's experience (\(\sim\)83.3% = 80 of 96). Furthermore, individual in-house standards (\(\sim\)62.5% = 60 of 96) as well as general tolerances, such as the widely known but recently withdrawn ISO 2768 (\(\sim\)66.7% = 64 of 96), were applied to assign tolerances. Only five respondents explicitly mentioned the determination of tolerances using established methods (such as worst-case and statistical tolerance analysis). Finally, five respondents reported specifying tolerances in agreement with others, such as the customer or production engineers. Nevertheless, the participants were aware of the importance of deviations and tolerances as Figure 3a illustrates. The majority (\(\sim\)56.6% = 56 of 99, 3 abstentions) of them claimed that at least every second problem that arose during production, assembly and use of products was caused by deviations and was a tolerance-related issue. This result shows a clear concordance with the well-known and widely quoted findings of [58; 59], stating that a \"large number of design/process alterations resulting in 67% to 70% of all changes related to product dimensional variation in aerospace and automotive industries\" [59]. Most respondents (94% = 94 of 100, 2 abstentions) confirmed the high importance of accuracy of their products--both in their geometry and in their resulting key characteristics (see Figure 3b). It is not surprising that nearly all the participants (\(\sim\)97.0% = 96 of 99, 3 abstentions) aimed to minimize scraps and rejects of their products. Hence, companies today still face the everlasting tolerance conflict between tight tolerances (to meet high quality requirements) and large tolerances (to reduce complexity and scrap rates during manufacturing). Nevertheless, 31 of the 53 design engineers (\(\hat{=}\)-58.5%) played it safe  
Figure 2: Classification of companies according to their size (=count of employees). (and confirmed their great respect for the specification of proper tolerances) by confessing that the assignment of tolerances was too tight (so-called \"angst tolerances\") and thus caused higher manufacturing costs. Experts expect that the specification of tight tolerances goes hand in hand with a strict philosophy on quality inspection in companies.