MK735 Mini Server / NAS Chassis

Features and Specifications

• Mini-ITX or Mini-DTX motherboard and low-profile (half-height) PCI-e cards only
• Full ATX power supply up to 170mm deep (SFX power supply supported but not recommended due to cable length)
• Drive bay handles 7 x 3.5″ disk drives
• Disk drives lock into bay using a unique “Flex-Tab-Slot-Lock” ™ method
• Optional brackets for two Solid State Drives located in the motherboard chamber
• Drives Under MotherBoard (D.U.M.B.™) computer chassis layout
• DIMENSIONAL:
  • Width: 248mm (9.75″), Depth: 242mm (9.5″), Height: 369mm (14.5″) 
  • Note that this chassis will fit on a 12” deep bookshelf and will still typically provide adequate airflow 
  • Motherboard underside to cover underside: 85mm
• WEIGHT:
  • Empty: Approximately 2.5kg (5.5 pounds)
  • Fully loaded: Approximately 7.7-8.2kg (17-18 pounds)
• COOLING:
  • Three independently cooled chambers: motherboard, drive and power supply. Each chamber is walled off from the other.
  • Three 92mm or 80mm primary cooling fans (2 in rear for drive bay, 1 up front for motherboard). Max fan depth: 25mm
  • Front fan provides airflow both above and below motherboard
  • Supports up to two optional 40mm fans on rear panel
  • Chassis “side vent” option for power supply included
• DOOR:
  • Allows access to recessed front panel power switch and USB ports without opening
  • Multiple front panel options
  • Opens a full 180 degrees
  • Grill design promotes excellent ventilation
  • Keyed door lock (optional)
  • Printed friction latch (optional)
  • Magnetic door latch (optional)
  • Features replaceable snap-in 3D printed hinges
• AIRFLOW FILTRATION – Available as an add-on package
  • Full front door and power supply air filtration using low cost, washable filter material
•  COVER:
  • Removes to the front after opening door
  • No screws needed, drop-in and slide design
  • Locked in place when the door is closed
• 100% 3D printable except for screws, optional lockset, optional magnets, and computer related hardware
• Uses just one size screw for chassis assembly: M3x12mm self-tapping truss head
• No exposed screws when assembled and closed, except for back and underside
• Can be printed using PLA (about 92% of parts by weight) and TPU or FlexPLA filaments
• Does not require supports when printing
• Minimal bridging
• Easy assembly with many snap-in parts
• Minimal post print processing of 3D parts (primarily brim removal on larger parts)
• Designed to be printed on consumer grade FFF/FDM type 3D printers capable of 0.2mm layers with a minimum build area of X:250mm Y:210mm Z:200mm

Project Files, Documentation and Objects

• The MK735 Mini Server / NAS design, project files and printable objects are copyrighted and released under a “Personal Use, No Derivatives” License. In other words, no sharing, no selling, and no remixing to sell or share.  Remixing for personal use is allowed.  The MK735 can be used in both home and work environment.
• 75+ pages of written project documentation is in .PDF format.
• Print parameter recommendations for every object.
• The project printable objects are in .STL file format.
• All .STL files are saved/published in millimeter units.
• The CAD files will not be released, with the following exceptions:
  • The front door “Logo Bar” (Door Grill Dovetail)
  • The front panel power switch/USB plates (Front Inserts)

These are released so you can create customized versions of those items to fit your own specific front panel hardware and vanity requirements.   The CAD files will be in .SKP format (Google Sketchup/Make).  You are allowed share your remixes of those two objects only, provided you do not sell them, and if published, you must do so stating the same restrictions.  You are encouraged to share those remixes.  If you share a remix of the Front Insert, please provide a vendor link or information about the switch, USB connector or other hardware the remix supports.

• As of the publication date, there are 92 3D printed parts created from 37 unique objects in this project. Two of those object/parts are printer test parts.  For objects that have multiple configurations, such as carriers for different fan sizes, the object is only counted once.  Two parts require more than 38 hours to print and an additional five take 8 hours or more.  A small number of objects are optional and may not need to be printed.

What You Will Need to Print this Project

• MOST IMPORTANT – An FFF/FDM 3D printer capable of .2mm layers with a minimum build area of X:250mm Y:210mm Z:200mm. Your build surface must be capable of retaining a large object during an extended print session.  The longest printing session is an estimated 44 hours.  ALL time estimates can be highly variable and depend on the printer you use, the speed that you push your filament and many, many other factors. The weight of the largest printed object will approach 600g.  Other non-FDM 3D type printers might be capable of creating the MK735 as well, but no others have been tested to date.
• You should expect a minimum of 220 hours of printer time.
• Your printer must be capable of printing both PLA and a flexible filament such as TPU or FlexPLA.
• A 0.4mm nozzle is suggested. There are a number of walls that are 1.67mm thick.  Those walls were designed that way because the Prusa version of Slic3r creates an optimal 4 perimeter wall of 1.67mm when the extrusion width of perimeters is set to 0.45mm, which is the default.  This is not a requirement but you may find you get faster and better results using those settings.
• You must be able to print the “MK735 Test Objects”. If you cannot print them within the expected tolerances, your chance of completing this project and the quality of the end product may be reduced.  The  “MK735 Test Objects” package is available here: MK735 Test Objects
• A computer and the usual software needed to slice the .STL files for use on your printer.
• About 1900g of good quality, high heat deflection temperature PLA filament. A filament based on NatureWorks’ Ingeo PLA 3D850, 3D870 biopolymer or an equivalent is recommended.  Both the 3D850 and 3D870 have about the same heat resistance, but the 3D870 has a massive advantage when it comes to impact resistance.  Using an “Annealing” process on the PLA printed parts in this project is not recommended.
• An additional 700g of good quality general purpose PLA filament. For color consistency, you may find that it’s better to just use the same high heat deflection temperature PLA filament, but for many parts it is not necessary. 
• About 250g of TPU (or Flex-PLA)  filament. You should try to use one that has a Shore Hardness of 98A.  However, some softer filaments may work if you increase the perimeters and infill.

Other Hardware Notes

Additional hardware is required to assemble the MK735 Mini Server.

View the MK735 Bill of Materials summary.

• Qty 50: M3x12mm Self Tapping Truss Head screws.  Required for assembly.  Actual number varies depending on which optional parts you install.  [What we’ve used]  
• Qty 28: #6-32 x 1/4” Truss Head machine screws.  Required to mount disk drives to drive rails.  Each disk drive and dummy drive will require four #6-32 screws in order to mount the drive rails. Those screws should have low profile heads.  If screws with high profile heads are used, the drive rails might not slide into the drive chamber.  The “MK735 Test Object” has a test hole with countersink in it that will indicate if the head of your screw is too high.  [What we’ve used]
• Qty 1: Front panel power switch.   [What we’ve used]   Knacro has several versions of this same switch that will work.  We recommend the shorter 60cm cable length for the MK735. 
• Qty 1: Front panel USB connector (optional).  What we’ve used:  [USB 3 Version]   [USB 2 Version Single]
• Qty 1: Lockset (optional but nice to have).  [What we’ve used]  The MK735 design also includes a printed friction latch if you prefer not to use a lockset.  
• Qty 4: 6x3mm N48 or N52 Neodymium Magnets (optional, really not needed).  These are used as magnetic door latches located at the top and bottom of the door.  Alternatively, you could also use eight 6×1.5mm magnets and stack them to get the 3mm height.  [What we’ve used]  
• Qty 4: #6-32 x 1/2″ machine screws (optional).  The MK735 includes two different motherboard pan designs, one uses the M3x12mm Self Tapping Truss Head screws (see above), the other uses the traditional #6-32 machine screws.  If you use #6-32 screws, those screws should be 1/2” long in order to engage properly into the plastic and retain your motherboard.  The “MK735 Test Object” has several test holes in it that will assist you in determining how well your selected screw will retain your motherboard.  We prefer the M3x12mm version over the #6-32 for mounting motherboards.
• Qty 3: Primary Cooling Fans.  Required for proper chassis cooling.  The MK735 design supports both 92mm and 80mm fans up to 25mm deep.  What we’ve used: [Our preferred choice: 92mmx25 4 pin]   [80mmx25 4 pin]   NOTE: Fans with the older “Molex” style connectors should not be used due to limited wire routing clearance.
• You will also need all other computer related components, such as power supply, motherboard, etc. 

Tools Required

• Metric dial calipers, 150mm or larger 
• Medium (#2) Philips head screwdriver
• Small to medium flat blade screwdriver
• Small wire brush
• Deburring tool, modeling knife or pen knife for brim and/or elephant foot cleanup
• Latex caulk or sealant (used for optional door magnets)

Cautions, Caveats and Considerations

• Make sure the filament you select is suitable for this chassis and is designed for the environment and conditions where the chassis is placed. PLA can be used for most of this project, but you should consider using an “Engineering Grade” with a high heat deflection temperature (HDT).  In addition to the potential heat issues, this may help prevent chassis sag over time due to the weight of disk drives. Other polymers, such as PETG, ABS or ASA with better HDT ratings could also be used, however those filaments are generally more difficult to print and both ABS and ASA will require enclosed printer chambers.  Conventional disk drives will be the largest weight component in a fully loaded MK735. Generally, as the capacity or R.P.M. increases, you can expect the weight of the drives to increase. The MK735 has not been tested for an extended period of time so the actual impact of that weight to cause sag is unknown.
• Cooling of the the chassis and your computer components is critical.  Always use good quality fans with a high reliability rating. The chassis must always be run with the three primary cooling fans (1 front motherboard chamber fan and 2 drive chamber fans) installed and operational.  For processors with a TDP rating of 45 watts or less, the minimum airflow for each fan should be 30 cf/m (50 m3/h).  If you install a higher TDP processor or additional PCI-e cards, you should make sure there is adequate airflow to keep both the chassis and computer components cool. 
• Make sure the completed chassis and all items placed in the chassis run cool and well within the heat deflection temperature of the filament you use. Only you can determine if this chassis will be acceptable and safe based on the components you place in that chassis. 
• There is about 25mm of clearance between the ATX power supply fan (50mm when using an SFX power supply) and the wall of the Power Supply Chamber. This may be less than your power supply manufacturer recommends. If you have any concerns about adequate airflow to the power supply, use the “side vent” version of the Power Supply Chamber.
• If your motherboard has the power connectors located on the far right side, you may need a cable extension on the MK735. This may be more of an issue if you use an SFX sized power supply where the unit is recessed deeper in the power supply chamber.
• This project requires the use of TPU or Flex-PLA filament.  By weight, about 8% of the parts are printed in flexible filament.  We suggest you use a harder/stiffer brand of flexible filament that lists in its specifications a Shore Hardness of around 98A.  Harder flexible filaments generally will feed better.  Direct drive print heads will usually have no problem printing FlexPLA or TPU filaments.  The success of printers with indirect filament feed systems, such as Bowden Tubes, can be highly variable.  In either case, if you have not yet printed with flexible filaments, you should test your printer’s ability to do so before attempting this project.
• During the assembly process of the MK735 chassis and when mounting computer hardware into the MK735, screws will be screwed into plastic. Plastic screw holes are more susceptible than steel to strip-out if you over torque the screw.  The correct procedure is to tighten the screw until it is fully seated and you start to feel a slight increase in resistance.  Then tighten no more than 1/8 of a turn.  Repeated disassembly and assembly will increase the chance of stripping out screw holes.   The “MK735 Test Object” has a number of test holes in it that will provide you a place to get a feel on how durable 3D printed holes actually are.
• Dummy Drives: If you install three or less drives, you do not need to use Dummy Drives if you leave an empty drive slot between each drive (EG: Load drives into slots 2, 4, and 6 leaving slots 1, 3 ,5 and 7 open). If your completed chassis will contain four or more drives, you should use a Dummy Drive in each empty drive slot to help provide equal airflow around all drives.  Assuming you follow that procedure, you will only need to print three Dummy Drives.  If you’d like, you can fill all empty slots with Dummy Drives regardless of the number of disk drives installed.
• Small, high power magnets can be dangerous. When inserting magnets into the magnet pockets, make sure they are well secured.  Once you insert the magnets into the pockets, place a small dab of latex sealant on top of the magnets so they are permanently sealed.
• Most 3D printable filaments are non-conductive. If your body is carrying an electrical charge (static charge), there is a higher risk of discharging that current to one of your system’s sensitive components.  With a metal chassis, any electrical charge you carry might be adequately discharged just by the process of touching or opening a grounded metal chassis.  This is not the case with a non-conductive, 3D printed chassis.  Make sure you properly and safely ground yourself beforehand.
• Radio Frequency Interference (R.F.I.): A non-conductive, 3D printed chassis will provide little, if any protection from R.F.I.  To date, we have not found this to be an issue with current computer equipment in the home or small office environments.  If you experience R.F.I. when using this chassis, consider using a spray-on coating designed to reduce R.F.I. applied to the interior surfaces.  If you continue to experience R.F.I. and are unable to mitigate it to an acceptable level, you should discontinue using the chassis.

What Others Have Said About the MK735

March 2019 – Brian Moses: His impressions of post-prototype unit 1.  This is the first MK735 seen by the public.

June 2019 – Brian Moses:  Printing and assembly of his MK735.  Brian was a member of the MK735 beta test team.

June 2019 – Brian Moses:  Brian’s Top Three DIY NAS Cases as of 2019.

March 2020 – Overclock3D / Mark Campbell:  This 3D Printed Case brings DIY NAS building to a new level.

April 2020 – @vindar (MK735 maker):  Very nice design, well thought out and easy to print. I hack your STLs to make a mini 4-bay (SFX power only) version as I do not have the room for the full version. Printed in black PETG without trouble. The chassis hosts a Supermicro x10sdv-6c-tln4f (Xeon 35W TDP). Temperatures are great with 3 fans at minimum speed: noctua 92mm for HDD, noctua 92mm for motherboard intake, noctua 140mm for interior. It is completely silent apart from the humming of the HDDs. Thanks for making this design. I love my new Freenas server !.

July 2020 – @martinpaoloni (MK735 maker):  …I’ve finished the build! Once again, I’m super impressed with the quality of the design and documentation. I’m attaching a few pictures of the final build…

March 2021 – @amirfelestian1 (MK735 maker):  …Very satisfied! Besides the fact the it is very dense NAS (Every inch is being used) and thus compact, I also had great time in printing, and assembling.

Where to Purchase

PLEASE, before you purchase the MK735, download and print the free MK735 Test Objects  first.

MK735 Test Objects Available Here

MK735 Available Here