50 is the default limit on a polyCube, so that's normal, but yes the bend's Curvature should go -180 to 180. Check mayainstallpath/scripts/others/performBend.mel for the section that starts with "float $maxCurv, $minCurv;" to check that the values are correct there. Looking at this also reminds me that 3.14 is 180 degrees…