In my last post I looked at Inventor’s new 3D Print environment and demonstrated how it can be used to setup an STL file to send to a specific 3D printer. New functionality is always exciting, especially when it occurs around other new technologies like 3D printing but there are existing features in Inventor that are also useful to validate designs before production.
One of the key factors in a design for 3D Printing is the minimum allowable wall thickness. Depending on the material and process that a part will be printed in there are different needs for thicknesses, gaps and more. For most geometry it is easy enough to design a model around those requirements. Sometimes though precisely defining a wall thickness can be tricky. When dealing with complex surfaces and loft features the wall thickness may vary unknowingly. To verify the wall thicknesses in a design before printing we can use a tried and tested inspection tool called Section Analysis.

Here I have a modified design of a plastic hub for an AndyMark wheel that is part of the kit of parts used in FRC competitions. I have reproduced a CAD model and made some changes to the inner bearing surfaces. To check that my model meets the 3D printing requirements I can start the section analysis tool from the inspect tab in Inventor. With this particular test I am verifying that there are no wall thicknesses that are too thin for the planned printing process.

In this particular test I need to verify that there is no location where an unsupported wall's thickness is below 0.7 mm or (0.027 in) thick. Starting the section analysis tool I select the Advanced option to analyze wall thickness on multiple planes.

In the Section Planes area of the dialog box I need to setup the orientation and location of the section planes to be analyzed. First I Select the face for the start plane and flip the direction so section planes are added to the inside of the part.

Next, I set the number of sections to analyze and set the total distance to include in the test. Here I have entered 10 for the number of planes and I’ve used the measure option to evenly space them from the top face to the bottom face of the part.

The total distance works out to 0.6875 inches. We can see here how the ten planes are evenly spaced within that distance.

In the Wall Thickness area of the dialog box I will leave 0.500 inches as the maximum and enter 0.027 inches as the minimum. I could also enter a value in a different unit than my default model unit. Since the specification from my supplier is in metric if I entered 0.7 mm Inventor would perform the conversion into my model unit for me.

All that is left to do is run the analysis and check the results. Clicking Apply in the dialog box executes the analysis. It may take a moment to complete but once finished you should see the model visualization update and the results area of the dialog display a tabled analysis result.

- A yellow hatch indicates that my walls fall within the allowable wall thickness range
- A red hatch indicates that the wall thickness is over the allowable thickness
- A blue hatch indicates where the wall thickness is below the allowable threshold
There are areas in red and areas in blue in my results. I can ignore the red areas as these don’t affect the printability of this part. There are some blue areas though which indicate a larger issue. Scrolling through the results table and checking off the Show Violating option gives me a clearer picture of the problems at these sections.

Notice that the table rows are colored corresponding to the section planes that violate the wall thickness test. In this case there is no one section plane that has results both over and under the allowable range. (If a section contained such a result the tabled row would highlight purple in the results area). The blue hatched areas show me that I have walls under the allowable thickness so I need to modify my design to increase the thickness in these places so the model will produce a quality print.
A nice thing about the section analysis tool is that by leaving the results visible the section analysis will automatically re-run after I make changes to my part. Here I have updated the inner diameter of the lower bearing surface. After updating the extrude feature my analysis automatically refreshes and I can see that there are no areas with a blue hatch.

In this particular case my section analysis is complete. This test is of primary importance since it has been performed in the same orientation as planned on the printer's bed. However a section analysis run in one orientation may not be enough to give a full picture of the part. I have walls in other orientations so running this analysis in plane perpendicular to my first test will yield different results.
When 3D printing a model keep in mind that the requirements for embossed/engraved features, wires, unsupported posts, gaps and other geometry are all different within the same print material. Here I just examined primary wall thicknesses. 3D printing services often have their own tools to check model geometry prior to production but using Inventor's section analysis tool will save time getting a valid file to your printer.
-DAP