Why tolerance stack up

It is assumed that most of the parts fall to the middle of the tolerance zone. We will calculate the overall maximum and minimum total stacked disk height using RSS Tolerance Stack up Analysis method.

RSS tolerance stackup analysis for a given problem can be done in the following steps:. Similar to worst case tolerance analysis, the first step in RSS tolerance stackup analysis is to create the dimensional chain. Total nominal disk thickness is calculated similarly to done during worst case tolerance stackup analysis by adding the nominal thickness of all disks. Mathematically standard deviation is equal to two times of process capability because the process is distributed on both sides.

Standard deviation for assembly is equal to root of sum of squares of the individual dimension standard deviation. Mathematically tolerance zone is equal to the multiple of required process capability and total standard deviation for the assembly. Lower the value of process capability, narrow will be the tolerance zone and higher will be the rejection.

According to the worst case tolerance stack up analysis disk stack height can vary from Whereas according to the RSS method disk height can vary from If you look at the results from Worst case and RSS method.

In the RSS method, the tolerance band is reduced. Therefore designers can give more flexibility to manufacturers. You can also use our worst-case and RSS method tolerance stack-up calculator for tolerance stack-up calculations. You can Download Tolerance stack-up calculation sheet here. To sum up, Tolerance stackup analysis is a very important part of product design. It also helps in reducing part cost. Various tolerance stackup analysis methods are available.

Got Questions? We will be happy to help. If you think we missed Something? You can add to this article by sending a message in the comment box. We will do our best to add it to this post. Make sure you understand the consequences of tolerance stacking before you calculate your stack-up. By contextualizing your final tolerance stack-up with manufacturing and performance, you can understand how large or small your tolerance stack can be without compromising success. This includes being conscious about how an individual part feature will interact with other component elements, making sure a part is machinable and within reasonable limits of manufacturing capabilities, and keeping track of important part characteristics like material selection.

Effective tolerancing facilitates high-quality builds with acceptable dimensions so the part can function in the way it was designed. Tolerance stacking involves finding the cumulation of all individual tolerances of a component or assembly in order to understand the potential range of final fits. Calculating your tolerance stack-up enables you to make sure parts can be properly manufactured as effectively as possible for the least cost.

Efficiently and accurately accounting for tolerance stacking is far easier with the help of a trusted manufacturer. Contact us today to get started.

For more tolerancing how-tos and guides , visit the Fast Radius resource center. Back to Overview. Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously. The cookie is used to store the user consent for the cookies in the category "Analytics". The cookie is used to store the user consent for the cookies in the category "Other. The cookies is used to store the user consent for the cookies in the category "Necessary".

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Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. If you want to learn more about this program, fill out this form and one of our team members will be in touch with you right away. Article Tolerance stacking Tolerance stack-up calculations represent the cumulative effect of part tolerance with respect to an assembly requirement.

This process for mechanical requirements is generalized in the flow diagram below. This simple comparison is also referred to as worst case analysis.

Worst case analysis is appropriate for certain requirements where failure would represent catastrophe for a company. It is also useful and appropriate for problems that involve a low number of parts. Low being defined as three or four parts. Worst case analysis is most often done in a single direction, i.

If the analysis involves part dimensions that are not parallel to the assembly measurement being studied, the stack-up approach must be modified since 2D variation such as angles, or any variation that is not parallel with the 1D direction, does not affect the assembly measurement with a 1-to-1 ratio.

Many companies utilize a statistical method for tolerance analysis. One approach involves a simple calculation using the RSS. Method, Root-Sum-Squared. Instead of summing tolerances, as in worst-case analysis, statistical analysis sums dimension distributions.

It is important to understand that the inputs values for a worst-case analysis are design tolerances, but the inputs for a statistical analysis are process distribution moments e.

Worst-case analysis also called tolerance stack-up analysis can be used to validate a design. Statistical analysis also called variation analysis can be used to predict the actual variation of an assembly based on the variation of the part dimensions. This approach requires distributions to be normal with all parts at the same quality level, i. Given the limitations of RSS, other methods for calculating assembly variation have been developed.

This method eliminates the limitations stated above. Analyses of all complexities, i. Companies can now do full Assembly Variation Analysis with tolerance analysis software. Assembly variation analysis provides insight required to identify the key part characteristics, KPCs that must be controlled in order to produce a product that meets the expectation of the customer.