MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
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(in cura it looked like the 4 little diamond cutouts at the center are not quite square, but no biggie.)
edit. : also thinking it might be a stronger part if you rotate the motor mounting holes 45*. -and actually since most people generally use only 2 screws per motor, maybe just use 2 holes in line with center axis.