Now I'm something special: material with a Mohs hardness above 3.5 you will not be able to edit satisfactorily with this set of files. And despite diamond occupation! As the price of the set beats again through .... You usually get exactly what you pay for!
In my case this means to hone rock, it takes an almost superhuman patience. Wood, however, is ridiculously easy.
Information Mohs hardness give eg encyclopedias such as Wikipedia.