An apparatus for producing a three-dimensional object by additive manufacturing, comprising: (a) a light source; (b) a carrier or carrier mount positioned above said light source, on which carrier a three-dimensional object can be produced; (c) a window mount (12a, 12b); (d) optionally, a fixed or removable window cassette connected to said window mount (12a, 12b); said window comprising: (i) an optically transparent semipermeable member, on which member a three-dimensional object can be produced; (ii) a fluid supply bed adjacent said semipermeable member and configured to feed a polymerization inhibitor through said semipermeable member, said supply bed having at least two opposing sides (iii) at least a first and second fluid orifice connected to said supply bed on opposite sides thereof and in fluid communication with one another through said supply bed; (e) a drive assembly operatively associated with said carrier and said window mount (12, 12b) and configured to advance said carrier and said window mount (12a, 12b) away from one another; (f) a first fluid switch connectable to said first fluid orifice when said window is present, or connected to said window mount and configured for connection to said window when said window is absent; (g) a second fluid switch connectable to said second fluid orifice when said window is present, or connected to said window mount and configured for connection to said window when said window is absent; (f) a fluid supply connected to both said first and second fluid switch (21a, 21b), said fluid comprising a polymerization inhibitor; and (g) optionally, a vacuum source connected to both said first and second fluid switch (21a, 21b). (a) a light source; (b) a carrier or carrier mount positioned above said light source, on which carrier a three-dimensional object can be produced; (c) a window mount (12a, 12b); (d) optionally, a fixed or removable window cassette connected to said window mount (12a, 12b); said window comprising: (i) an optically transparent semipermeable member, on which member a three-dimensional object can be produced; (ii) a fluid supply bed adjacent said semipermeable member and configured to feed a polymerization inhibitor through said semipermeable member, said supply bed having at least two opposing sides (iii) at least a first and second fluid orifice connected to said supply bed on opposite sides thereof and in fluid communication with one another through said supply bed; (i) an optically transparent semipermeable member, on which member a three-dimensional object can be produced; (ii) a fluid supply bed adjacent said semipermeable member and configured to feed a polymerization inhibitor through said semipermeable member, said supply bed having at least two opposing sides (iii) at least a first and second fluid orifice connected to said supply bed on opposite sides thereof and in fluid communication with one another through said supply bed; (e) a drive assembly operatively associated with said carrier and said window mount (12, 12b) and configured to advance said carrier and said window mount (12a, 12b) away from one another; (f) a first fluid switch connectable to said first fluid orifice when said window is present, or connected to said window mount and configured for connection to said window when said window is absent; (g) a second fluid switch connectable to said second fluid orifice when said window is present, or connected to said window mount and configured for connection to said window when said window is absent; (f) a fluid supply connected to both said first and second fluid switch (21a, 21b), said fluid comprising a polymerization inhibitor; and (g) optionally, a vacuum source connected to both said first and second fluid switch (21a, 21b).