![]() In simpler terms, this is the head, shoulders, knees and toes of tolerance stacks. If you are new to a technology or team this can be a very good place to start, to help ground you in what’s what and guide you to: “ noticed this” or “ can you explain why this is like this” - all the observations that get you up to speed on the engineering OCD of “ why”? In the figure below you can see the subsystems for this linear rail: Figure 2: Subsystem Break down Create Interaction MapsĪnother method to break things down is to create interaction maps between your subsystems or parts. ![]() ![]() Today, we be doin’ it live folks (Lee-Roy Jenkins!) so let’s just jump in. How do you do this? Sometimes there is a super logical method and some days you just pick something and start. The first thing I like to do with a big problem is to break it down into a series of smaller problems, or subsystems. So let’s pretend we need to do tolerance stacks for this assembly - where do we start (and remember this is more about a process to yield repeatable results for you as a design engineer)? Figure 1: GIF of Assembly Break Down the Subsystems Here’s some example CAD to help us start to break down the tolerance stack process: a linear rail from GrabCad. Starting with a Simple Example: Linear Rail Let’s dive in with a simple example to start. Will the square peg fit in the round hole.Will the rotating encoder disk be too close to my PCB receiver or too far away?.When most people talk about tolerance stacks they are likely addressing only one of these steps, but all three is where you need to get to! This is beyond just: 1) will my parts fit/go together 2) will it perform 3) Can steps (1) and (2) be done repeatedly. ![]() With each stack you ask: will the variability I naturally get from part to part in my assembly lead to malfunctions of my design? The basic concept of tolerance stacks is simple addition and subtraction. Now you’re in the real world and a solid tolerance stack can be the difference between success and failure. You likely did tolerance stack ups in your first Intro to Engineering course homework on a made up assembly that maybe felt kind of pointless because it wasn’t actually an assembly you made and so success = course credit. ![]() Fundamentals Refresh: What is a Tolerance Stack? Here I’m going to walk you through the flow of how to set up tolerance stacks, why you do tolerance stacks in the first place, and most importantly, how you determine you are done with the tolerance stack.Īs we go through the examples, I recommend downloading this free tolerance stack calculation workbook, which will enable you to calculate your own tolerance stacks. Oh hey - I caught your attention! Guessing it was the 5-oh-one in the title, up from the 101 you might already be familiar with ( self high five for engineer David trying to be a marketer). ![]()
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March 2023
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