First, identify the target dimension of interest. In this example, it is the clearance between the blocks and the pocket.
Next, starting from one end of the target dimension, draw vectors through each relevant dimension so that you create a complete loop reaching the other end of the target dimension. Be sure to assign a number to each vector for easy reference.
Then, establish a positive direction. For this example, we define positive as towards the right. Consequently, vector 1 will have a positive value, while vectors 2 and 3 will carry negative values according to the chosen direction.
By following these steps, you can systematically map the dimension loop and ensure consistency in your tolerance analysis.
All tolerances must be symmetric and bilateral. In this example, dimension 1 is initially given as a unilateral tolerance. Therefore, to convert it, we first center the nominal value and then assign an equal bilateral tolerance. As a result, the dimension becomes 35.95 ± 0.05.
Furthermore, the picture below shows examples of different types of tolerances. However, for the purpose of tolerance analysis, all of these variations are considered equivalent. Thus, Equal Bilateral Tolerancing must always be applied to ensure consistency and accuracy in the calculations.
Be sure to use the converted bilateral tolerance as required, and also ensure that you apply the correct signs according to the loop diagram. Additionally, the columns highlighted in blue will be calculated automatically, which means you don’t need to enter values manually. By following these steps, you can maintain accuracy and consistency throughout the analysis.
The ‘Nominal’ column shows the expected or nominal value of the gap between the blocks and the pocket. Meanwhile, the Max and Min Condition columns illustrate the extreme cases for each type of analysis.
As expected, the Worst Case scenario predicts the largest range of variation. For example, under the Max Condition, the clearance could reach up to 0.95. However, under the Min Condition, interference occurs, meaning the blocks would not fit in the pocket, as indicated by the negative value.
In addition, the calculator performs a Root Sum Square (RSS) analysis, which essentially calculates a standard deviation for the assembly, creating a bilateral tolerance defined as:
Tolerance_assembly = ±3σ_assembly.
This means that in most cases, both blocks will fit inside the pocket, and interference is unlikely.
Furthermore, the tool performs an adjusted RSS analysis. This type of analysis is particularly suitable for high-volume production processes, where the mean value of a process may shift by 1.5σ_assembly, providing a more realistic prediction of tolerances in practical manufacturing scenarios.
Note: To perform a meaningful RSS (Root Sum Square) stack-up tolerance analysis, some assumptions are made: Independent Variations, Normally Distributed Variations, and Tolerance Accumulation Linearity
This is an example of how to use the ME Virtuoso Tolerance Analysis Calculator
Two blocks are to be inserted in a pocket, as shown below. We would like to understand what is the clearance that we will have between the blocks and the pocket. Dimensions and tolerances are provided in the image.
Identify the target dimension of interest. In this case, the clearance between the blocks and the pocket
Starting from one end of the target dimension, draw vectors through each relevant dimension, in order to create a loop so that you reach the other end of the target dimension. Assign a number to each vector.
Assign a positive direction. In this case positive will be towards the right, so that vector 1 will have a positive value, and vectors 2 and 3 will have negative values.
All tolerances must be symmetric bilateral. In this example, dimension 1 is given as unilateral. In order to convert it, we must center the nominal value and give it an equal bilateral tolerance. This results in: 35.95 ± 0.05
In the picture below you can find examples of different types of tolerance. For the purpose of tolerance analysis, all of these are equivalent and Equal Bilateral Tolerancing must be used.
Make sure to use the converted bilateral tolerance, and make sure to use the correct signs per the loop diagram. Columns in blue will be automatically calculated.
Note about Sigma Level: This allows you to specify the manufacturing capability for a specific dimension. For example, if the manufacturer of a part can achieve 6sigma production, this column would allow you to specify this by entering a value of ‘6’. However, if left blank, a standard sigma level of ‘3’ is used. This means that “Tolerance = ±3σ”
The ‘Nominal’ column shows the nominal value of the gap that we will have between the blocks and the pocket. Max and Min Condition show the extreme cases for each analysis type.
Worst Case scenario, as expected, predicts the largest range of variation. That is, under Max Condition, the clearance could be up to 0.95, however, under Min Conditions, there would be interference (blocks won’t fit in the pocket), as shown by the negative sign.
In order to understand what is more likely to happen, we need to make use of statistical analysis.
The calculator also does a Root Sum Square (RSS) type of analysis, which is essentially calculating a standard deviation for the assembly, thus creating a bilateral tolerance for the assembly: Toleranceassembly = ±3σassembly. This shows that in most cases both blocks will fit inside the pocket, and interference is not likely.
Additionally, the adjusted RSS analysis is performed. This analysis is more suitable for high-volume production processes where the mean value of a process may be shifted by 1.5σassembly
Note: To perform a meaningful RSS (Root Sum Square) stack-up tolerance analysis, some assumptions are made: Independent Variations, Normally Distributed Variations, and Tolerance Accumulation Linearity
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