# SOLIDWORKS 2020 Torsion Continuity Relation (G3)

Article by Scott Durksen, CSWE updated December 19, 2019

###### Article

SOLIDWORKS 2020 adds an additional sketch relation to provide torsion continuity (G3) between splines and any other sketch entity in a 2D Sketch.  The torsion relation applies to splines and one of these sketch entities:

• Spline
• Arc
• Conic or elliptical arc
• Model edges that are linear, circular, conic, parabolic, elliptical or spline-based

The continuity of a surface is described by the term ‘G’ which stands for Geometry, relating to how surface faces meet and transition.

In this example we have a sketch with two arcs on the sides and a spline connecting them at the top.  Curvature combs will be added to help visualize how the transition takes place.

SOLIDWORKS Sketch Entities

### G0 – Continuity

This represents geometry connected with a coincident relation, but there can be a sharp edge.

SOLIDWORKS Sketch with Coincident Relation

### G1 – Continuity + Tangency

This represents connected geometry and adds a tangent relation.  It may appear to be a smooth transition between the sketch entities, but the curvature combs show a different story.  The curvature values at the connection point don’t match up.  If we extrude a surface and turn on zebra strips, the faces coming together no longer look smooth.  You would also see this in real life with a polished surface under lights.

SOLIDWORKS Sketch with Tangent Relation

SOLIDWORKS Zebra Stripes for Tangent Relation

### G2 – Continuity + Tangency + Curvature

Adding an additional relation ‘Equal Curvature’ improves the transition by having the curvature values match at the point of contact.  The zebra stripes show a much cleaner surface.  Yet you can still make out the location of where the faces meet.  In this case we have arcs which have the same curvature throughout and then it needs to transition fairly quickly to the higher curvature of the spline.

SOLIDWORKS Sketch with Equal Curvature Relation

SOLIDWORKS Zebra Stripes for Equal Curvature Relation

### NEW! G3 – Continuity + Tangency + Curvature + Torsional

SOLIDWORKS 2020 adds a new Torsion Continuity sketch relation which provides G3 continuity between geometry.  It essentially helps with the rate of change of curvature to balance the transition and generate an even smoother surface.

SOLIDWORKS Torsion Continuity Relation

SOLIDWORKS Sketch with Torsion Continuity Relation

SOLIDWORKS Zebra Stripes for Torsion Continuity Relation