We present an interface for 3D object manipulation in which standard transformation tools are replaced with transient 3D widgets invoked by sketching context-dependent strokes. The widgets are automatically aligned to axes and planes determined by the user’s stroke. Sketched pivot-points further expand the interaction vocabulary. Using gestural commands, these basic elements can be assembled into dynamic, user-constructed 3D transformation systems. We supplement precise widget interaction with techniques for coarse object positioning and snapping. Our approach, which is implemented within a broader sketch-based modeling system, also integrates an underlying "widget history" to enable the fluid transfer of widgets between objects. An evaluation indicates that users familiar with 3D manipulation concepts can be taught how to efficiently use our system in under an hour.