In a 3D-printing system, a deposition head comprising a band assembly having a body and a band for compacting a filament onto the surface of an object being manufactured. One or more actuators are mounted on the assembly body and are used to shape the band to a desired contour. The band is connected to the one or more actuators, is curved toward the surface of the object to enable contact with the surface, and is capable of being driven along its length by one or more drive wheels that are under the control of a controller. The drive wheels are configured to advance the band along its length by a first distance and in response to a first signal from the controller. The controller provides the first signal based on an estimate of thermoplastic build-up on a portion of the band that overlaps the point of compaction.