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The addition of Multi-Body part modeling has widened the envelope of Top Down design. This method of design involves a single part that carries multiple solids. The chief benefit lies in the fact that parts that are to be assembled together are created in the same environment, same part, using the same sketches and features. The separate solids do not need to be created from separate Derived sketches, and lack problems that components created in an assembly carry.  Here are some areas to look into:

  • Splitting Solids into Multi-Body Parts
  • Creating New Solids and Adding Features
  • Shared Sketches
  • Derived Components

Splitting Solids into Multi-Body Parts

We can create a final form object as a solid part component, and then use the Split Command to break it into multiple solid bodies within the same part file. These can be derived off to separate files as needed.  The chief benefit to this methodology is that the multiple parts are cut from a final form. When fitted together they will form the intended final shape and size required.

This approach reduces oversight by sharing the use of the same sketches and features to perform numerous tasks on mating objects. Areas that require a precise fit are easier to work with, simpler in design, and require less manipulation that other methods.

We also reduce modeling failures that all alternate methods of modeling share: broken references to projected geometry in linked component features. With this method all the referencing is done together in one file..


This method limits oversight as well. The parts will fit together perfectly.  That is why its great for Weldments, parts that slide together into a single mass, and so on.

Creating new solids and adding features

While splitting a single solid derives a clean part with limited dependencies, we can also add new solids from Inventor’s sketched features. This is as easy as creating an Extrude for example, and telling Inventor to either add it to another solid body, or instead to create a separate new solid.


The sketched features can easily reference other solids in the same part by Projected Geometry or Cut edges. Everything lies in the same file, so your level of control and design awareness is substantially higher.

There is no real difference to modeling in a multi-body part, with the exception that features are now directed to which solid they are intended to affect.

Shared Sketches

Since everything in the part file has direct access to all sketches and features firsthand, we can form adjacent features from a common sketch. This can simplify a design significantly.  In the image below, I needed a track added to the clamp body. An extrusion was added to the right body solid using a sketch. That same sketch can now be used to Cut the same shape from a part that has to fit into the track.


Derived Components

The individual solids remain together in their multi-body part, and can be broken out into separate part files through Derived Components. When the Derived Components dialog appears, simply select the solid to be included in the new component part file.  It is that simple, and it is super clean.



Top Down design is a large subject, and multi-body design is really but a fraction of that concept. It does none the less provide a solid foundation for designs that are intended to have key components that fit together in one manner or another.

The examples I used here are from a simple bracket. However, there is no limit to the scale of this method. Huge airframe structures can be managed with he same design philosophy.

Less sketching, less projected geometry, less derived component steps, less room for disconnect and failure, and reduced oversight, and greater design awareness.

Read more – Simplified Sketching