NAS Raspberry Pi Zero W for one 3.5" HDD

I am using a raspberry pi zero w with one 3.5" HDD as an offsite mirror storage for my backups. A pi zero fits perfectly for this use case as it is cheap and doesn't need much power, performance is not really relevant as I am limited to 2 MB/s.

Parts required

• Raspberry Pi Zero W
• micro USB OTG adapter. Choose a short one, there isn't much space.
• USB HDD adapter board. Mine is from Seagate external HDD cases (don't remember which HDD it was, possibly their “Expansion Desktop” series, see picture). Others might fit too. 
  • USB cable from OTG adapter to HDD. Choose a short one, there isn't much space.
  • Power supply from external HDD. It should be 12V
  • Male and female cable fitting the power supply / adapter board. The female side will be mounted to the case (the hole has a width of 11mm). I used this one (5.5mm/2.5mm).
  • rubber parts (blue things on the pictures) from the external HDD (you probably can leave them away or print them).
• 12V to 5V voltage regulator
• optional: 2x Wago clamps for flexible cables for 3 wires (alternatively solder it)
• Some wires and two with dupont terminals to connect to the Pi GPIO header (used for power supply)
• M3 heat threaded inserts OD 4.2 or 4.5
• M3 countersunk screws

Parts to print

• Print case
• Print one of the lids. Likely the one without the mounts for the USB hub is preferable as it will have a little bit more space.
• If you don't have the rubber things: print one of the two versions of the “rubber parts” 4 times

Assembly

Notes:

• The case is very tight. Use short cables.
• There are mounts for a USB hub to make a USB port available outside of the case. I did not use it as I had lots of issues with my pi and suspected the hub as issue. In the end it turned out it was a faulty pi but never returned to using the hub. Using the hub might cause issues with the power supply.

Assembly steps:

1. Insert heated inserts into the case. The screws for the pi will be screwed directly into the plastic. No heated inserts required here.
2. Install female side of the power connector to the case
3. Assemble the power supply system
   1. Connect male and female power cable through the Wago clamps
   2. Connect the voltage regulator to the Wago clamps
   3. Connect the pi to the output of the voltage regulator. Refer to a pi zero GPIO documentation for the pins. Connect + to the 5V pin and - to a GND pin
4. Install HDD
   1. Screw rubber things to the HDD
   2. Install the adapter board to the HDD
   3. Connect power and USB to the board
   4. Insert it into the case
5. Install Pi
6. Screw top part onto the main case