This functional platform jack prints fully assembled without supports.
UPDATE [7/21/2015]: We have uploaded an updated platform jack with stronger scissor arms, improved axles to stop the arms from separating, and a larger gap between the screw and crossbeam to fix the fusing issue. We printed the updated version with a 0.3mm layer height and 15% infill in 4 hours.
UPDATE [7/22/2015]: For anyone having problems with the scissor arms fusing together we have uploaded a modified file with the tolerance increased from 0.5 to 0.65 mm (The axle tolerance is unchanged).
This model prints fully assembled without supports. Our print time for the original model was 6 hours on a Replicator 2. We printed it with a 0.2 mm layer height, 15% infill, and a raft. The screw will be fused to the top crossbeam initially, but if you give it a clockwise twist it should separate and turn freely. Before attempting to twist the screw, inspect the print to make sure that none of the pieces are fused together.
The updated model was printed in 4 hours on a Replicator 2 with a 0.3mm layer height and 15% infill.
The jack extends 10.5 cm. The updated jack was able to support 20 pounds before failing (while fully extended).