I've always just been content to enjoy my fave razors without giving much thought to the design parameters involved
I think that sums up why I love DIY so much. you don't even know what you're not thinking about until you try to do it yourself. With mechanical things or even with something like music or cooking, taking a whack at it gives you a whole new perspective.
is metal important? maybe. let's try and find out
(for the record my instincts say that it is important. in the long run I don't think PVC will yield the required rigidity. if a replace my epoxy with some metal though, that would make things much stiffer)