DeMello, A.J. Arbelaez, D. Bianculli, D. Brown, A.P. Corlett, J.N. Dougherty, J.R. Humphries, D.E. Jung, J.-Y. Leitner, M. Marks, S. McCombs, K.A. Ray, K.L. Sadlier, D.A. Schlueter, D. Wallén, E.J. JACoW Geneva, Switzerland 978-3-95450-182-3 10.18429/JACoW-IPAC2017-TUPAB122 English 1602-1604 TUPAB122 undulator photon simulation experiment laser Contribution to a conference proceedings 2017 2017-05 http://dx.doi.org/10.18429/JACoW-IPAC2017-TUPAB122 http://jacow.org/ipac2017/papers/tupab122.pdf The Linear Coherent Light Source II (LCLS-II) project, an upgrade to the free-electron laser facility at SLAC, is replacing the undulator system from a fixed gap to a variable gap system to enable tuning of the photon energy range. The LCLS-II project will include a soft x-ray (SXR) beam line and a hard x-ray (HXR) beam line. The SXR undulators are conventional vertical-gap horizontally-polarizing devices while the HXR undulators are novel horizontal-gap vertically-polarizing devices. This paper describes in detail the development of the SXR mechanical support structure and drive system. The effort has included extensive analysis of the various components to ensure that the undulators will perform within the design specifications. Engineering simulations undertaken and experiments performed to validate the computer modeling are presented together with measurement results from prototype and pre-production undulators.