knuckle down to vs turn to

knuckle down to

turn to

verb
  • To consult for advice or help. 

  • Used other than figuratively or idiomatically: see turn, to. 

  • To become, to degenerate into. 

  • To direct one's attention or efforts toward something. 

  • To start to do or to use something in an attempt to deal with a difficult and unpleasant situation. 

How often have the words knuckle down to and turn to occurred in a corpus of books? (source: Google Ngram Viewer )