A new rapid prototyping process, variable lamination manufacturing (VLM), has been developed to reduce building time and to improve the surface finish of parts by using a 4-axis-controlled hotwire cutter and expandable polystyrene foam sheet as a laminating material of the part (VLM-S). The objective of this study is to reconstruct the surface of the original 3D computer-aided design (CAD) model in order to generate mid-slice data using the advancing front technique (AFT). The generation of 3D layers by a 4-axis-controlled hotwire cutter requires a completely different procedure to generate toolpath data unlike the conventional RP CAD systems. The cutting path data for VLM-S are created by VLM-Slicer, which is a special CAD/CAM software with automatic generation of 3D toolpath. For the conventional sheet type system like LOM, the STL file would be sliced into 2D data only. However, due to the use of thick layers and a sloping edge with the first-order approximation between the top and bottom layers, VLM-Slicer requires surface reconstruction, mid-slice, and toolpath data generation as well as 2D slicing. Surface reconstruction demands that the connection between the two neighboring cross-sectional contours use the triangular facets. VLM-S employs thick layers with finite thickness, so that surface reconstruction is necessary to obtain a sloping angle of a side surface and the point data at a half of the sheet thickness. In the process of the toolpath data generation the surface reconstruction algorithm is expected to minimize the error between the ruled surface and the original parts.