Anyone ever sharpened a Spong bean slicer?

I picked up a Spong bean slicer which I remember my Mum using years ago, but it is sadly blunt.  Has anyone every sharpened one of these?  Shame if I can't use it for my piles of runner beans, I remember my Mum whizzing through piles of runner beans years ago.

I am going to take a look tomorrow as I now have a runner bean mountain in my fridge and don't want to waste them!  Will post back.