Geometric Operations - Things to Consider - Part 2

Source:
Richard St. Arnauld, Sr. Tool Designer
George Mock, , Mechanical Engineer

Geometric operations in solid modeling are volumes created using cross-sectional planer profiles and dragging functions, such as blends, extrudes, sweeps, revolves, fillets, corner rounds, and local surface deviations. It should be noted here that in a solid modeling system these geometric operations result in a single closed solid entity. Similar operations are available in surface modeling that result in one or more individual surface entities.

Some "hybrid" modelers can support both at the same time.
These volumes may have constant or variable cross sections and linear, multi-linear, curvilinear, or axisymmetric paths. The common naming conventions used for such entities are: extrude, sweep, blend or transition, and revolve.

Here are some more things to consider when construction geometric operations.

Profiles, Chamfers, and Fillets

When sweeping cross-section geometry into a solid keep that geometry as simple as possible. Do not include fillets, radii, and chamfers (unless you have an incomplete or non-tangent one). Adding these features to the resultant solid keeps them as intended (a fillet/blend is a fillet/blend not a rounded solid face) and in some systems you are limited to the number of entities that you are allowed to sweep. Also make sure that your geometry is planar before it is swept. Some non-planar geometry can be swept but can result in an invalid or unstable solid.

Modifying Profiles

One thing to look for when evaluating SM systems is what techniques are available for modifying profiles. Some systems allow you to change profiles by changing dimensions. Some require that you extract the defining curve, modify it, then replace the original curve. Or, you can just replace the curve with a new one. Other systems won't let you modify the profile. You must delete the part and start over, or modify it with Boolean operations.

Plan Your Edge Sequence

Before attempting to apply fillets or radii to a solid spend some time studying the model and plan the sequences of edges to which you want to apply them. Think about the way the model would be manufactured. Use the "undo" command (if your system has this feature) when the result is not as expected.