What’s the Best Tolerance Stack Method?

When it comes to calculating tolerance stacks, there are many different methods. Some people simply take blank paper, then make a quick sketch and scribble out some numbers. While that may work for a very simple stack, it’s obviously not a very methodical approach! A better way is to use Excel or even special software for tolerance stacks to calculate an answer.

Even when using Excel, there are two schools of thought for performing a stack:

  • Some folks prefer to use a stack method that separates everything into an absolute maximum or minimum dimension, and then create two columns to stack the max and min results.

 

  • Others insist on translating everything to a nice symmetric plus/minus tolerance, centered around a nominal.

Both methods will work — it often comes down to how you were taught to perform stacks. Here’s my two cents’ worth: I prefer the max/min method, especially when GD&T is involved. Because geometric tolerancing is based on limits (think about MMC and bonus tolerance) it is usually easier to plug those into a spreadsheet.

For more information check out the Tolerance Stacks course that we offer. Most of the class is devoted to this max/min method, but we also teach the plus/minus method as an alternative. We also have an Excel template available on our “free downloads” page.