Methods, systems, and apparatus, including medium-encoded computer program products, for creating toolpaths of support structures for 3D printing include, in one aspect, a method including: obtaining a perimeter of a first slice of a 3D model; identifying at least one portion of the perimeter of the first slice that extends a distance beyond a boundary of the 3D model for a second slice below the first slice, the distance being greater than a threshold amount defining an unsupported overhang; creating a support path that follows a shape of the at least one portion of the perimeter, the support path having a lateral offset from the at least one portion of the perimeter, the lateral offset being a fraction of the 3D print bead width, and the fraction being a positive number less than one; and adding the support path to toolpaths for the second slice.