Raspberry Pi 4 NAS with 2x 3.5" bays

Features

• 2 emplacements for 3.5" Hard disks, connected via USB3 to the Raspberry Pi
• 140x25mm fan emplacement at the front for efficient cooling of the Raspberry Pi and hard drives
• Internal Power-supply 5V/12V
• Main power switch and fuse accessible at the back of the unit

Bill of material

3D printed parts

• 1x GRILL
• 1x HOUSING
• 1x RACK

Electronics

• 1x Raspberry Pi 4 model B [RPI]
• 2x USB3-to-SATA Adapter with 12V input (Poppstar Festplatten-Adapter (USB 3.1 Gen 1 Typ A) Sata USB Kabel für externe Festplatten)
• 1x Fan 140x25mm [FAN]
• 1x Industrial power supply 54 W, 6 A, 5/12 V (MEANWELL RD-50A) [PSU] 
• 1x Fuse 5x20mm (LITT 02181.25MXP)
• 1x Fuse Holder (Fuse holder FPG1 ø5x20mm) [FUSE_HOLDER]
• 1x Power Rocker Switch (RND 210-00553) [SWITCH]
• 1x C14 plug (KES 1 S Cold-device built-in plug C14) [POWER_PLUG]
• 2x DC Jacks 1.4mm Inner, 3.4mm outer diameters (NES/J 135)

Hardware

• 4x M3x20mm bolt
• 6x M3x12mm bolt
• 4x M3x8mm bolt
• 8x M3 nut
• 4x M3 washer
• 4x M2x8mm bolt
• 4x M2 nut
• 4x standard computer fan screws (don't know the reference)
• 4x 22mm diameter circular rubber feet

Build Instructions

Printing

• The grill prints face-down on the print bed, it needs internal support at each corner for the nut fittings.
• The Housing print with the edge interfacing with the grill down on the print bed, it also needs support at each corner for the nut fittings used for the rack assembly. A brim can be useful to reduce wrapping on this part.
• The rack prints with the back of the unit down on the print bed (where all the connectors will be), it requires support to the print bed at each corner for the bolt holes.
• Use PET or other temperature resistant material (PLA is not suitable as sustain exposure to temperatures above 40°C will degrade the material).
• Account for the material shrinkage ! In my case I printed X and Y dimensions at 100.4% for all 3 parts, using Prusa PETG.

Assembly

1. Press-fit 4 M3 nuts, one in each corner of the GRILL, it's a bit tricky because they got from inside, use a bolt to press them well into the fitting.
2. Press-fit 4 M3 nuts, on in each corner of the HOUSING
3. Assemble the FAN to the GRILL using the 4 fan screws, make sure the cable is at the right side of the GRILL when looking inside the unit (the bottom of the GRILL is indicated by the two circular emplacements for the rubber feet)
4. Assemble the HOUSING to the GRILL using 4 M3x12 bolts
5. Assemble the PSU to the RACK using 4 M3 washers and 4 M3x8 bolts
6. Press-fit 4 M2 nuts at the top of the RACK, from the inside at the RPI emplacement
7. Assemble the RPI to the RACK
8. Wire the electronics (see section below)
9. Place your Hard-disks into the RACK's slots
10. Slide the RACK into the HOUSING

Electrical wiring

Optional FAN driver circuit (can work with Vcc=5V or Vcc=12V):