The top plates of the X-axis holder of my ANET A6 printer cracked for unknown reason. Perhaps I fastened some screws too much.
Since I couldn't find any drawings of the ANET A6 frame, I designed my own spare parts.
The parts were designed to ensure a tight fit. I used 60 % infill (octet), so that the parts have a high stability. It was not necessary to file away some material to install the new top plates, however it largely depends on the quality and precision of the acrylic parts that came with your printer kit.