Introducing the Five Flute Tolerance Analysis Calculator

A free interactive visual calculator for building worst case and RSS assembly tolerance stackups.

William Burke

William Burke

Five Flute Founder & CEO

Here at Five Flute we’re obsessed with mechanical and electrical engineering challenges. Our software is built to help engineering teams collaborate around all phases of development: design, build, test, and deliver. But there are so many interesting and challenging problems within these phases that we also want to help engineers solve. To that end, I’m excited to introduce you to our free online tolerance analysis calculator! It’s a browser based interactive calculator for building worst case and RSS assembly tolerance stackups. You can use it to iterate on dimensional tolerances during design, estimate manufacturer performance, and recover from manufacturing mistakes. Best of all it’s a free tool that gives you visual results and tabular data output that you can share with anyone via email.

🔎 You can find it here: https://www.fiveflute.com/tools/tolerances

💡Pro tip: Bookmark it so you can find it when your next tolerance challenge pops up.

How to use the Five Flute tolerance analysis calculator

First, it helps to know a bit about how RSS tolerance analysis works. We’ve written two helpful guides to bring you up to speed in case you need a refresher.

Intro Guide - good for understanding the basics.

Advanced Guide - good for calculating failure rates and dealing with trickier tolerance problems.

We’ll step through how to use the tolerance analysis calculator using a simple mechanical assembly example.

Example walk through

In this example there is a clevis mount that secures one end of an actuator by bolting to a rod end bearing. The assembly consists of the clevis mount, a rod end bearing, a machined spacer, and a flat washer.

rod end clevis assembly isometric

Build your tolerance stackup

In order for this assembly to work there must be a large enough gap for the washer to be inserted easily when sliding the bolt through the clevis. This gap, shown below as assembly gap, cannot be too large or else the bolt will not maintain enough preload on the spherical bearing and the clevis will be too deformed when this bolt is tightened. The critical dimensions in the tolerance stackup and tolerance stack equation are shown below.

rod end clevis assembly section view

Tolerance stack equation

Enter dimensions and tolerances

Now simply enter the dimensions and tolerances in the input table of the Five Flute tolerance analysis calculator according to your tolerance stack equation. Make sure you give each dimension a name so the results are clear. Note the negative dimensions in this table! The calculator will sum these dimensions to compute the assembly dimension, thus a subtracted dimension in a tolerance loop should be entered as a negative value.

tolerance calculator - dimensions table

Enter assembly dimension limits

Next, you should enter the upper and lower limits for your computed assembly dimension. In our example we know that the assembly gap must be greater than zero, lets say 0.001” so assembly is easy, and no more than 0.022” so as not to damage the clevis while preserving functionality. Enter these limits in the design targets for assembly dimension section.

tolerance calculator - assembly limits

Note: you would have to figure these limits out on your own for each assembly you analyze, but that’s where the fun is in engineering.

View and interpreting results

Now that you’ve entered your individual and assembly dimension values, you are ready to view your results. First check out the Outputs: Stackup plot with worst case & root sum squared (RSS) tolerances section. The calculator automatically builds a plot of each individual dimension and how they sum in the tolerance stack. This section shows a graphical representation of the individual dimensions and how they sum according to the stack equation.

tolerance calculator - output stackup plot

The assembly level results include graphical representations of the assembly dimension and tolerances for each analysis type.

tolerance calculator - output stackup plot results interpretation

Next check out the Outputs: Dimension analysis with worst case and RSS tolerance failure rates section. This section shows all of the results in a tabular form, including left and right tail failure rates for the assembly limits you entered.

tolerance calculator - output table

Save and share your results

When you are done and you want to save or share your results, simply email yourself a copy.

five flute tolerance calculator - email share button

You’ll get an email from support@fiveflute.com that looks like this.

five flute tolerance calculator - email results example

All your results are right there, along with a link to return the Five Flute tolerance analysis calculator to view and update your analysis at any time. You can share this with anyone by simply forwarding this email 🙂

If you have any trouble with the calculator or have suggestions for how to improve and extend its functionality we’d love to hear from you at support@fiveflute.com. That’s it! Good luck with your next tolerance analysis problem, hopefully this makes it easier!