hammer (away) at sth meaning

• [American slang]
  1. Lit. to continue to do a task that requires much hammering.
    The roofers are hammering away at the job, trying to finish before night.
  2. Lit. to pound at or on something, such as a door.
     Who is hammering away at the door?
    The police are hammering at the door.
  3. Fig. to dwell overly long on a point or a question.
    Stop hammering away at the same thing over and over.
    The agents asked question after question. They would not stop hammering at the issue.