Create manufacturing tolerances in NX CAM

NX CAM QuickTip | How to create manufacturing tolerances based on PMI dimensions

Create manufacturing tolerances with the PDTM in NX CAM

The PMI Dimension Tolerance Modeler (PDTM) is a useful tool for Siemens NX that simplifies the creation of tolerances on a workpiece. The basis for this are the PMI dimensions, which are attached directly to the 3D model as product manufacturing information. The PDTM automatically reads these PMIs and makes them available in a dialog for the creation of manufacturing tolerances.

What are PMIs and what are they needed for?

PMIs are Product Manufacturing Information that are attached to the 3D model or assembly during the construction process and stored within the file.

PMIs include the following:

  • Surface information
  • Geometric dimensions and tolerances
  • Form and position tolerances
  • Text notes
  • Machining method (reaming, drilling, milling, etc.)

These dimensional and manufacturing tolerances, which are normally only available in a drawing, are specified as the PMIs of the 3D model and allow it to provide manufacturing-relevant information on which other processes such as CAM and CMM can be based in order to automate the manufacturing processes.

Why do you need tools like the PDTM?

Design usually works with nominal dimensions, taking tolerance specifications into account. In CAM programming, however, the middle dimensions on the tolerance center are used for programming.

In the case that a component has dimensions whose nominal dimensions are not at the center of the tolerance, Siemens provides a tool in NX, the PDTM, to correct the dimensions in the 3D model and create manufacturing tolerances. This tolerance middle dimension module automatically shifts the contours of the component including the adjacent geometries to the tolerance center according to the PMI specifications.

PMIs Comparison nominal dimension and middle dimension
Nominal dimension vs. Middle dimensions

How to use the PDTM in NX is explained in detail in this NX Tutorial:

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Step-by-step guide:

  1. We open NX and load the part with PMI dimensions.
  2. We open the post-installed PDTM tool (where to download and what you need to consider during installation is explained in the following section).
  3. The PDTM tool lists all PMI dimensions that are included in the workpiece. We click on the PMI dimension that we want to bring to its middle of its tolerance.
  4. We select "Middle Dimension". 
  5. Depending on the geometry for which the tolerances are optimized, you need to define which surface(s) should be moved. For example, for holes or radii, this step can be skipped.

    To define the faces to be moved, we click on "Cycle Through Faces to be Moved".  The first click selects the left face, the second click selects the right face, and the third click selects both faces and move them towards each other.

    Note: If an additional face has to be moved, it can be selected using the "(Un-)Select Additional Faces to be Moved" button.
  6. We click on "Apply" to apply the center tolerance. 
  7. We proceed in the same way for the other PMI dimensions.  However, pay attention to the surface selection in step 5! 
    Not always both surfaces should be moved equally, respectively further surfaces must be considered. In the video we show you a few examples.

Where do I find the PDTM?

To use the PDTM, you have to download and install the NX tools from Siemens. The NX-Tools are little applications, which help you in your daily work inside NX. However, they need to be installed separately and are not part of the default NX installation.

Download the NX-Tools from the Siemens Support Center

To get the NX tools installed, you need to download them from the Siemens Support Center. At the "Downloads" section you can find the relative base version, together with the current batch release version and the related add-ons. Within these add-ons you find the NX Tools on the left side followed by the download files.

After the NX Tools have been downloaded and unpacked on a centralized storage, which is accessible by CAM workplaces, furthermore steps need to be done. Detailed information about the installation process can be found in the NX Tools install directory within the subfolder "help" subfolder.

Two essential steps that need to be done when installing the NX tools are shown in the video.

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The PMI Dimension Tolerance Modeler is a useful tool to create manufacturing tolerances based on PMIs. To use the PDTM, you first must download and install the NX tools from Siemens. 

Martina NafzMartina Nafz
Marketing Manager

Author of the article / Autorin des Beitrags

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