Examples:

• This makes no sense to knuckle down on them right now.
• Just tell him to knuckle down, tell him he's got to do better.
• If you will agree to knuckle down and study, I will treat you to a sumptuous dinner at Les Habitants.
• The second is to knuckle down and work together, try to work out how best we can help you.
• These are questions that one should knuckle down and begin to confront once the problem of debt, fiscal pressure, and the monetary unionhave been resolved.