Autodesk Inventor Design Accelerator: Tolerance Calculator

January 30, 2013, post by Robert Reid, Manufacturing Solutions Engineer:

The “Tolerance Calculator” helps the end user to perform calculations of closed linear dimension chains within the Part environment, or the Assembly environment. The calculator can work in the following two basic modes:

• Calculation of the resulting dimension including tolerances (check calculation):
Performs a check verifying correctness of design dimensions
• Calculation of tolerances of the closing chain element (design calculation)

Read the full tip.

In the following example, we will look at a simple shaft made up of 3 sections.
The 2 end journals are machined for positioning of bearings to be press-fitted up against the journals:

Using the “Tolerance Calculator” Tool, we want to find the Dimension and Tolerances of DIM “A” to ensure our bearing housings are located correctly.
To access the “Tolerance Calculator”:
In the Assembly environment, click the Design Tab:

Click the black down arrow on the Power Transmission Panel:

Click on “Tolerance Calculator:

The above screen-shot represents the “default” each time the dialogue is opened.
The Graphics area represents the number of shaft segments to analyze.
The Dimensions List will represent the tolerances for each shaft segment
The Upper Right Hand Corner has 2 icons:

File Naming is to give you a choice in what you what to name the analysis
Results will be an HTM file we will look at later.

In my shaft example, I have 3 sections. These will be represented by D1, D2, and D3.
Notice how the Direction arrows are all showing the same direction to the right. At this point I want to add 1 more section which represents the overall shaft length.
So in the Dimension List section, click on “Click to add dimension”

There are 4 sections to complete the Tolerance Analysis.
Add the tolerance values for each shaft segment.
Click on the tc9 icon to open the Tolerance Dialogue Box:

Enter all Tolerance Values:
• Add a Name
• Model Value (Note the + Plus Sign, this keep all dimension in the same direction)
• Tolerance Type: Symmetric, Deviation, or Limits/Fits
• Upper and Lower Limits based on Tolerance Type

Click the Green Check Mark to accept
The Black Down Arrow will let you choose what type of dimension it will be:

D1 in this example will be Normal

D2 will be the Resultant Tolerance, so Resultant will be checked:

Since D2 is now the Resultant, all Values are grayed-out except for its Nominal Dimension:

Fill in Values for D3, which for this example is a Normal Dimension:

The Last Value to be filled in is D4. D4 is the overall length that the other D1 and D3 will be subtracted from to find the Resultant of D2.

Note Model Value has been changed to a Negative!

Also the Tolerance type is Symmetric:

D4 is also the Closing Dimension.

The Graphics area now shows us the correct configuration to find the Tolerances of D2:

CLICK CALCULATE!

The design is within Design Compliance, and we can see our Results of D2:

Click on the Results Icon, and the HTM Report id displayed:

The Tolerance Result is also displayed in the Model Browser:

Happy Designing,
Bob Reid

(*This tip will work for either Autodesk Inventor 2012 or 2013 versions.)

Robert Reid graduated from Middlesex College in New Jersey with a Degree in Mechanical Engineering Technology. With over 25 years of Industrial Machine Design, including Wire Drawing Machinery, Plastic Processing Machinery, & Packaging Machinery, Robert has held various positions within the workforce, including, Manager of Engineering; Sheet Extrusion Dept, Manager of Engineering, Chief Design Engineer. He is currently an Autodesk Inventor Certified Expert.

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