Tolerance analysis - Part 1

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Hello, my name is Thom Tremblay from Concepts and Design.

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This course is on a modern approach to creating documentation.

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The learning path for this course will look at annotating a 3D model and sharing the annotated model,

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analyzing tolerance relationships in an assembly, and then sharing the results of that analysis.

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This is the fourth course in the series.

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This chapter will be in two parts and we'll be focusing on setting up a tolerance analysis.

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We'll validate the current settings for the analysis, set up an analysis using the assembly constraints,

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modify tolerances based on the results to get closer to the ideal condition.

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And then we'll use the Results View to take a closer look at what that tolerance stack up means for real world production needs.

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I'll begin by opening the Tolerance Analysis Assembly file.

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Then I'll activate the Tolerance Analysis Level of detail representation.

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This will reduce not only the number of components shown on the screen but the number of components occupying memory space in Inventor.

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Selecting the annotate tab, we can see all of the 3D annotation tools available to us.

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There's also a very thoughtfully placed Assembly Section View tool.

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We'll use the Half Section View tool and select the origin YZ plane for the assembly.

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After clicking OK, this will remove half of the assembly.

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You'll notice that the bearings and shafts were left unsectioned.

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Now, before we go farther, I want to point out that the top set of shafts and bearings are held together using constraints.

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The lower set of the discrete gear, bearings, and shaft are not held in place.

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This is to represent an assembly that perhaps you imported from another CAD system.

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Starting the Tolerance Analysis Tool will open the Tolerance Analysis Panel on the right-hand side.

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Presently, there are no tolerance stack up studies.

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The Tolerance Analysis Tool is a 1D tool.

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It will detect the tolerance stack up along a single axis.

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Let's begin by looking at the settings.

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At the top of the dialogue is the default tolerances.

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If your model doesn't have tolerances built into the dimensions or into the features,

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you can set a default tolerance value for those sketch dimensions and features.

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This will also set an overall default tolerance for models that don't have a default tolerance.

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Also in the dialogue, you'll be able to choose what analysis target you're using.

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We'll start out with worst case.

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And you can also set a default statistical quality metric and value.

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We'll leave it with process capability.

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Down at the very bottom, you can even set your annotation scale and colors.

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Let's begin by creating a new stack up.

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You begin a new stack up by defining the mating condition that you want to base the stack up from.

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In this case, I'll zoom in and I'll use what is the bottom of the pocket cut for the bearing,

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and then wait for the Select Other Option to come up, so I can select the back face of the outer race of that bearing.

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Once that's done, I'll follow the red arrows where it's looking for me to select an annotation plane.

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I'll use the YZ plane of the origin.

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Because these components were assembled together in the proper way, I'm offered the opportunity to use the Assembly Constraints and Joints option.

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If I wanted to do this manually, I could change this to selecting the components.

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The results give me four different paths.

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I'll use the first one which uses the gasket cover top and gasket stand top constraints.

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Once I've selected that, I'll click OK.

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And it will start to generate the tolerance values.

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In the pane on the right, you can see all of the different dimensions,

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and the tolerance values either assigned to them automatically or the values that were extracted from the 3D model or the 3D annotation.

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Looking down at the bottom at the stack up, it shows that I have an opportunity for interference for 36,000 of an inch.

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Knowing this, I can look back at the tolerances applied,

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and see where maybe there's some discrepancies or opportunities to make changes to the model to accommodate for this.

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The first thing I'll do is I'm going to take the tolerance on both bearings down to 3,000.

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That reduces the number.

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Then I'll take a look at the gasket.

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I can change it from a simple symmetric tolerance to setting it to limits where I can establish the tolerance for that component more precisely.

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At the bottom where I'm seeing the results, I can also take a look at the contributors.

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And I see that the greatest contributor is the gear housing, dimension one of the gear housing.

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If I scroll the upper section back up to the top, I see that the gear housing depth is set with a fairly high tolerance value.

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So I'm going to change that to a symmetric value and change it to 5,000.

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Immediately, I see this reduces the contribution that that gear housing is having in the tolerant stack up.

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And if I switch to Results View, I can see that it's dramatically reduced the worst-case scenario.

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Speaking of which, I'm going to scroll the dialogue to the right and I'll change the display from worst case to showing the RSS value.

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I can also change it to a statistical value of the percent yield.

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And here it's showing me that I've got a 99.9999% yield using the current tolerance values.

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Let's pause at this point and in the next video, we'll take a look at how to use components and their faces to create a tolerant stack up.