Step 1: Acquire Materials & Tools

You'll need:

An old hard disk drive
A set of small screwdrivers with Torx / star heads (these are fairly cheap)
A DIY clock mechanism (there are a bunch of these)

If you can, try to get a variety of old hard disk drives as they vary quite drastically in how they are constructed and how easy / hard they are to disassemble and modify.

In order to have the least amount of hassle, you'll ideally find one such as this, which is constructed and held together only by screws. Therefore, these models can be taken apart using only manual screwdrivers, without any use of power tools. Other Instructables rely on drilling or other more elaborate methods of taking the drive apart. Without the need for that, this project can be done quickly by anyone with minimal tools.

Step 2: Initial Disassembly

First, take of the circuit board on the underside of the drive, which is usually held in place with a few Torx screws.

Some crews might be hidden under stickers, so be sure to check under them.

Step 3: Take Off the Strong Magnet

The arm that reads the disks is controlled with the help of a strong magnet. I think, the hard drive looks more interesting when it is removed, as you can see the wire windings of the arm that moves across the disks.

In order to remove the magnet, remove the screws holding it down and then pry it off using a flat screwdriver. You might have to use some force as these magnet are very strong.

While we don't really need the magnet for this project, there are a few Instructables with ideas for using it in other projects.

Step 4: Disassemble the Disk Stack

In order to remove the individual disks, the arm needs to be swung to the side and moved out of the way.

Depending on the type of drive, there might be a small piece of plastic in the top left corner that limits the range of motion of the arm. Remove it first.

Then using a screwdriver remove all the (tiny) screws holding the disk stack together. The individual disks are separated by aluminum rings. At the bottom of the stack sits the motor. Remove the screws that hold it as well, leaving a hole in the case for the clock mechanism.

Step 5: Mount the Clock Mechanism

Place the clock mechanism (with the clock hands removed) behind the hard drive case, centering the clock stem in the middle of the hole left by the motor. Should you not be able to fit the clock flush with the back, due to bits of the hard drive case being in the way, these parts can be ground away using a file. The hard drive cases are usually made of soft metal, which is easy to work with.

Once the clock sits close to the case in the spot where it should be mounted, mark the spots, where the screws holding the motor used to be. Rotate the clock mechanism until at least one of these marks hits the battery case of the clock.

Using a sharp tool or a small hand drill, drill a hole through the plastic of the clock's battery compartment. Make the hole large enough so that the motor screw fits through. We'll use the hole to the clock on to the back of the hard drive case using one of the removed screws. Using one screw is fine here, it only needs to hold the light clock mechanism.

Step 6: Build It Up Again

Once the clock mechanism is firmly mounted, we can tackle the aesthetics and reattach the pieces that make up the look of a hard drive. Using some double-sided tape, hot glue or other other glue, reattach a hard drive platter to the front, covering the clock mechanism.

Make sure not to re-add too many of the removed platters to the stack, so as to allow the clock hands to still turn freely.

Mount the clock hands and cut them to size, so that they won't touch the hard drive's arm when turning.