Sorry to raise an old post, but thinking it through further there may be a way to produce light structures more simply.
1) Print a mould (mold) using a reprap. You could do this in sections for a large item such as a wing or airship hull and bolt them together or mount them to a wooden board. You could also position spars and reinforcement such as cardboard tube in the mould or smaller reprapped parts for mounts or hinges.
2) Use a release agent in the mould such as wax.
3) Mix and pour hard expandable foam into the mould. Use foam such as this which goes hard when cured.
Hard cure foam
4) Once cured you separate the sections and remove the part complete with internal reinforcement. The mould is reusable many times.
5) For extra strength, wrap with carbon fibre or leave as is.
1) Print a mould (mold) using a reprap. You could do this in sections for a large item such as a wing or airship hull and bolt them together or mount them to a wooden board. You could also position spars and reinforcement such as cardboard tube in the mould or smaller reprapped parts for mounts or hinges.
2) Use a release agent in the mould such as wax.
3) Mix and pour hard expandable foam into the mould. Use foam such as this which goes hard when cured.
Hard cure foam
4) Once cured you separate the sections and remove the part complete with internal reinforcement. The mould is reusable many times.
5) For extra strength, wrap with carbon fibre or leave as is.