Hammer out
Definition 1 of 2
Pro Tip 1/3Negotiation imagery
The phrase implies a vigorous discussion, often picturing the back-and-forth effort in reaching an agreement. 
The committee will have to hammer out the finer details of the policy soon.
Pro Tip 2/3Extended effort
Usually suggests a lengthy process with considerable effort, not something resolved quickly. 
It took weeks to hammer out the terms of the contract.
Pro Tip 3/3Collaborative connotation
Indicates a collaborative process where all parties contribute to the final solution. 
The differing parties managed to hammer out a compromise.