SOLIDWORKS Trim Surfaces Types: Standard vs Mutual

Surface modeling is different than solid modeling.  When creating a solid feature that overlaps another solid feature, the overlapping area is automatically removed by default. Surface features that overlap must be manually trimmed. Surfaces can be trimmed where they intersect with another surface, a plane, or a sketch.  There are two SOLIDWORKS trim surfaces types: Standard and Mutual.

Trim Surface Type: Standard

The Standard type is where a single entity (a surface, plane, or sketch) is used as the trimming tool.

Here is an example of a Standard trim. This part has two surfaces – a circular surface with both ends open and a rectangular planar surface. The desired result is to remove the planar surface that is outside the circular surface, keeping the area inside as a bottom for the circle.

Standard Trim

When trimming, we can either choose what we want to keep or what we want to remove, whichever is the easiest to select.

In this example, it is easier to remove the outside of the planar surface.

Here is another Standard trim, this time a sketch is used to trim a surface, again removing what’s outside of the sketch.

The options “Natural” and “Linear” only come into play when the trim tool does not entirely cross the surface to be trimmed.

Here’s an example using a sketch to trim a surface, removing the area below the sketch.

The “Linear” option extends the endpoints linearly to the edges.

The “Natural” option extends the endpoints tangentially to the edges.

The “Split all” option changes how trimming tool edges are created on the trimmed surface. In this example, the curved surface will be used to trim the spline-shaped surface using the “Linear” option.

With “Split all” cleared, two areas are detected.

With “Split all” checked, four areas are detected.

Trim Surface Type: Mutual

The Mutual trim type is used when more than one trimming tool is needed. Here is an example where a planar surface passes through the middle of a circular surface. What we want is the upper part of the circular surface with a circular planar surface closing the bottom. Picking a single trimming tool will not accomplish that. Select both surfaces as trimming tools and select what we want to either keep or remove.

The Preview options are very helpful in understanding what the result of the trim operation will be. We can show what’s included, excluded, or both.