ax to grind vs enthusiasm

ax to grind

noun
  • A proposition or point of view to advocate, especially motivated by self-interest. 

  • A grudge or grievance, with implications of confrontation. 

enthusiasm

noun
  • Something in which one is keenly interested. 

  • Intensity of feeling; excited interest or eagerness. 

How often have the words ax to grind and enthusiasm occurred in a corpus of books? (source: Google Ngram Viewer )