Folks looking to use a gouge to make a notch like the one I did: don’t start with a 30mm wide gouge in ¼ inch thick hardwood. That stop cut is challenging. It’s trivially easy in ¾ pine with a 15mm wide gouge (one sharp rap with a mallet will do), and then the cut to meet it can be done by hand, rather than with a mallet.
Any curvature between about a 4 and a 7 will work.