How do you perform a worst-case tolerance analysis on a complex assembly of engineering drawings?

2 Assign tolerances to each dimension

The next step is to assign tolerances to each dimension of the assembly. Tolerances are the allowable variations in dimensions that ensure the proper function and quality of the product. You can use standard tolerance tables, industry standards, or customer requirements to assign tolerances. For example, if you are using ANSI Y14.5, you can use the tolerance symbols and modifiers to specify the type, size, and location of tolerances for each dimension.

3 Identify the worst-case scenarios

The third step is to identify the worst-case scenarios for each critical dimension of the assembly. A worst-case scenario is a combination of tolerances that results in the maximum possible deviation or error in a dimension. You can use a systematic approach, such as a stack-up analysis, to identify the worst-case scenarios. A stack-up analysis is a method of adding or subtracting the tolerances of each component along a dimension to determine the total tolerance of the assembly. For example, if you are analyzing the distance between two shafts in a gearbox, you can add the tolerances of the shaft lengths, the gear thicknesses, and the bearing widths to find the worst-case scenario.

4 Calculate the worst-case values

The fourth step is to calculate the worst-case values for each critical dimension of the assembly. The worst-case values are the nominal values plus or minus the worst-case deviations or errors. You can use simple arithmetic, algebra, or trigonometry to calculate the worst-case values. For example, if you are calculating the worst-case diameter of a gear, you can use the formula D = d + 2t, where D is the worst-case diameter, d is the nominal diameter, and t is the worst-case deviation.

5 Compare the worst-case values with the specifications

The fifth step is to compare the worst-case values with the specifications or design requirements of the assembly. The specifications or design requirements are the acceptable ranges or limits for each critical dimension of the assembly. You can use graphs, tables, or charts to compare the worst-case values with the specifications. For example, if you are comparing the worst-case clearance between the housing and the bearings of a gearbox, you can use a bar chart to show the minimum and maximum values of the clearance and the specification limit.

6 Evaluate the results and make adjustments

The final step is to evaluate the results and make adjustments if necessary. The results of the worst-case tolerance analysis show you the potential risks or problems in the assembly due to the variations in dimensions and tolerances. You can use the results to assess the feasibility, quality, or performance of the product. If the results are unacceptable or unsatisfactory, you can make adjustments to improve the design, such as reducing the tolerances, changing the dimensions, or modifying the components.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?