Straighten Oblique Axes Out of Contour Polygon
The parts of the oblique axes that are out of the contour are drawn straight with the "Draw line perpendicular outside contour polygon" option in the axis settings.
Select the axes you want to straighten outside the contour and enter Axis Settings .
Check the feature Draw line perpendicular outside contour polygon.
Your oblique axes will be drawn straight out of the contour.