Tips & Tricks: Using Skeleton Models for Top Down Design

Sometimes you need lengthy explanations and demos to learn how to do something new with your CAD design software. More often, you just need a sentence or two to realize something’s possible.

This post covers some of those one-sentence tips and tricks for working with standard and motion skeleton models. If you’re not familiar with top-down assembly modeling, this video offers a great explanation:

If you’re already jumping in, you might find these pointers helpful:

Skeleton Models

  • Used for design framework, space claims, interfaces between components and assembly references. Note:
    • Skeletons should contain sketches, curves, surfaces, and datums only.
    • Skeletons are not factored into mass property calculations.
  • Use skeleton models in conjunction with publish geometry and/or copy geometry to share design information.
    • Publish geometry in the source part creates a “container” of references that can be shared with a target part later.
  • Use “multiple_skeletons_allowed ” to share design information between multiple skeletons.
  • You can also create skeletons in subassemblies.

Model tree showing skeleton parts

Image: Skeleton in model tree.

Standard Skeleton Model Methods

  • For skeletons that drive geometry and assembly position, note:
    • Use publish geometry and/or copy geometry that references the assembly context (see icon shown at top in the image below).
  • For skeletons that drive geometry only (constraints/connections added later in the assembly context), note:
    • Use publish geometry and/or external copy geometry that references the skeleton model directly.
    • This allows placement between skeleton coordinate system and component coordinate system.


Image: When you click the icon at top, the Copy Geometry feature will look in the current assembly to reference the source part. Use the icon at bottom if you want the feature to reference the source part directly (not through the assembly), in which case you "place" the feature in your target part as shown in the Placement dialog, as shown below).

Placement dialog

Image: Component Placement dialog

Motion Skeletons Overview

  • Motion skeletons are used as a design framework of mechanized assemblies. Note the following:
    • The motion skeleton is a .ASM file that contains a standard skeleton and body skeletons.
      • Standard skeletons contain design geometry.
      • Body skeletons are assigned geometry from the standard skeleton.
  • The first body skeleton created is assumed as the “ground” component and is fixed. Subsequent body skeletons are assigned assembly Connections assumed from sketch constraints (point/point, point/line).
  • Create parts in the assembly context.
    • Parts are “attached” to body skeletons and assume their motion definition. No assembly connections are created manually.

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