Unless you know you have a flexy nib, you shouldn't. Too much force can cause your tines to sproing, and then you need a new nib (or get a nibsmith to fix it, w

Unless you know you have a flexy nib, you shouldn't. Too much force can cause your tines to sproing, and then you need a new nib (or get a nibsmith to fix it, which might be more). Most of my pens have nibs that aren't designed for much line variation.