Recovering data from hard drives that have been physically damaged is an extremely complicated process that usually requires the expertise of a professional. In most cases, damaged drives will need to be opened up in order to recover the data that has been written to them.
Opening a hard drive is something that needs to be undertaken with the utmost of caution, simply because the slightest amount of dust or static electricity can do irreparable damage. Once you understand the hard drive recovery process, you will quickly see why professional help is usually warranted.
Most companies that specialize in recovering data from damaged hard drives use special clean rooms for opening up the drives. These rooms are designed to minimize the risk of any dust or static electricity affecting the drive. This is an extremely important step. If any dust happens to get on the hard drive plate, it can make the problem exponentially worse, decreasing the chances of being able to recover any data.
The technicians who work on these drives also wear clothing that is designed to reduce the risk of any static electricity building up. Again, this is to minimize the chance of the drive being damaged while it is open.
Once the hard drive has been opened, there are a variety of different techniques that technicians can use to recover the data. In some cases, they may be able to repair the hard drive itself by replacing broken or damaged parts. In other cases, however, the damage may be too severe to fix the original drive.
In these severe cases, one of the only options available is to make a disk image that data can be recovered from. This process is not entirely foolproof but it does at least provide a chance of getting some of the lost data back in cases where there is significant damage to the hard drive.
As you can see, hard drive and other types of data recovery is a complicated process. It requires skill and expertise that is beyond what most people have.
Even if you were confident in your ability to open up a hard drive and recover the data, you would need a place to do it where there was no chance of dust or static electricity harming the drive. This is practically impossible to achieve outside of a clean room environment, which is why your best bet is typically to send the hard drive out to a data recovery company rather than trying to recover the data yourself.