An apparatus includes a platen and a dispensing system overlying the platen. The dispensing system includes a powder source. The dispensing system further includes a powder conveyor extending over the top surface of the platen, rings arranged coaxially along a longitudinal axis of the powder conveyor, and a cap plate extending along a length of the tube. The powder conveyor is configured to receive powder from the powder source. The powder conveyor is configured to move the powder. The rings form a tube surrounding the powder conveyor to contain the powder. Each concentric ring includes a ring opening. Each ring is configured to be independently rotatable. The cap plate includes a cap plate opening. The powder is dispensed from the tube through the ring opening and the cap plate opening when the ring opening and the cap plate opening are aligned.