I have expanded the expansion plates during fabrication and now the plates will not contract, why is this?

If you expand the plates prior to the fabrication of the mounting arms for a better grip on the device, this is fine. However, you must make sure that the gear threads are free from all debri, including cleaning agents, prior to the contraction of the plates. Debri in the threads of the gear system will prevent the plates from collapsing back to the 0mm position.