Apparatus for the manufacture of three-dimensional objects

A method for recirculating powder in an apparatus for manufacturing a three-dimensional object from powder, the apparatus including a work surface having a build area, the method comprising:

• (a) providing powder in a powder repository, wherein said powder in the powder repository is one of fresh powder, excess powder or a blend of fresh powder and excess powder;
• (b) transferring the powder from the powder repository to the work surface;
• (c) distributing the powder across the build surface and resulting in a portion of the powder defining excess powder;
• (d) returning the excess powder from the work surface back to the powder repository;
• (e) monitoring the amount of powder in the powder repository relative to a predetermined amount of powder;
• (f) delivering fresh powder from a powder tank to the powder repository when the amount of powder in the powder repository is less than the predetermined amount of powder, and not delivering fresh powder from the powder tank to the powder repository when excess powder is being returned to powder repository and the amount of powder in the powder repository is greater than the predetermined amount of powder.