From Longman Dictionary of Contemporary Englishknuckle down phrasal verb informalWORK HARDto suddenly start working or studying hard SYN get down to If he doesn’t knuckle down soon, he’ll never get through those exams. to He is clearly ready to knuckle down to the task. → knuckle→ See Verb table
Examples from the Corpus
knuckle to• Social workers and their managers are clearly ready to knuckle down to the task of making the policy work for users. 