Tech Tip: How to Use Construction Lines

What’s the Purpose of Construction Lines?

Construction lines serve as non-geometry references that define structural intent without contributing to actual model geometry. This separation between reference and model geometry is fundamental to parametric CAD design, allowing you to build fully defined, easily modifiable models where design intent is captured through relationships rather than static geometry.

Construction Lines in Sketches

When sketching, construction lines can serve various purposes: references for constraints and dimensions, axes for downstream features, and more.

Construction lines are useful for almost all sketch constraints, from mirroring or symmetry inside a sketch, to tangent relationships for arcs and splines, to general references like parallel or coincident. In these cases, construction lines provide sketch references that fully define the sketch contours and are used in downstream features.

Just like any other sketch line, construction lines can be dimensioned to assist various applications. One of the most common use cases for dimensioning a construction line is to define the magnitudes or directions of spline handles or conics to better control the curvature they create.

Construction Lines as Part Studio Feature References

Once construction lines are created in sketches, they can be used as references for features. Construction lines are great axis references for revolve or mirror features. The same construction line can even be used multiple times across features to ensure concentricity between components.

In addition to using them as feature references, mate connectors can be attached to construction geometry in reference sketches to serve as skeleton references in assemblies further downstream.

Construction Lines in Assemblies

Many master sketches contain construction lines for positioning. This is handy when building a top-level assembly. With mate connectors attached to construction lines, they can become mating references for parts and assemblies to maintain the intended structure from sketch to assembly.

Construction Geometry in Drawings

Construction geometry is not only for parts and assemblies. Use lines and centerpoints as construction references on drawings. Centerlines can define lines of symmetry in a part and can even be dimensioned. For circular geometry, centerpoints can be added to denote center reference points for circles and arcs.

These are just a few examples of where construction lines add much-needed references to your Onshape designs. Try them out for yourself and check out the rest of Onshape’s recent technical blogs here.