A removable window cassette (100) for a bottom-up stereolithography apparatus includes (a) a light-transmissive window (110) having a rigid bottom portion (112), a semipermeable top portion (114), and a fluid flow region therebetween; (b) a circumferential frame (120) surrounding said window and into which said window is recessed, said frame having a top portion, a bottom portion, and an internal wall portion (120C), said frame internal wall portion defining with said window semipermeable top portion a well into which a polymerizable liquid may be received; and (c) a plurality of clamp draw-in pins (140) connected to said frame bottom portion and extending downward therefrom; and (d) at least a first and second port (150A, 150B) connected to said frame bottom portion, with said first port in fluid communication with said second port through said window fluid flow region.