The ornamental design for a build plate for a three-dimensional printer, as shown and described.
FIG. 1 is a top perspective view of a design for a build plate for a three-dimensional printer;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines that are immediately adjacent to the shaded areas and define unshaded regions depict the bounds of the claimed design, while all other broken lines are directed to environment. The broken lines form no part of the claimed design. The wire frame lines shown throughout the views indicate surface contour. The attached Appendix includes additional images and drawings of the build plate for a three-dimensional printer.