3D Printed DIYbio Centrifuge (V3)

About: ProgressTH is a Bangkok-based design lab & media platform focused on developing and promoting opensource technological solutions.

Microcentrifuges are small centrifuges used in laboratories for basic mixing and separation/extraction protocols. We've used ours mainly for DNA extraction protocols likethis one here.

This design is meant to be flexible. It includes a removable motor mount that can be redesigned to take any motor you like. The overall length of the motor including the shaft shouldn't exceed 70mm though.

There is also enough space inside the case for a microcontroller or other components you might want to add.

Supplies:

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Step 1: 3D Printing, Assembly, & Electronics

3D Printing

The STL files are included in the Instructable but are also available at Thingiverse here if you are more comfortable with viewing/downloading them from there. Along with the STL files is the SketchUp 2019 file as well as an OpenSCAD file for the rotor.

These are included in case users want to modify the rotor, motor mount, or anything else they want.

Electronics

The electronics are very simple (see the diagram and photo of the electronics in place).

Wiring: Power comes through the barrel adapter’s positive terminal. It goes through a rocker switch — to the motor’s positive contact and from the negative contact to a microswitch’s COM terminal. Then from the normally open — or N-O terminal — it goes back to the barrel adapter’s negative terminal.

Connectors: We soldered wires onto the motor, limit switch, and rocker switch. We used screw terminals and jumper wire connectors to make the design modular so we could go back in and modify, repair, and swap out motors for experimenting more easily.

Make sure you solder wires to your rocker switch and then feed them through the mounting hole on the side of the case before connecting the wires to your motor if you are soldering everything.

Just remember, centrifuges vibrate a lot and we've had screws come out of their terminals. Small blobs of hot glue can be used to keep them in and if you need to re-wire something you can pry the hot glue out relatively easily with strong tweezers or small needle-nose pliers.

Assembly

Once your parts are printed and your electronics are together, assemble the printed parts. We will be using friction welding but you could also use hot glue if you prefer. If you are unfamiliar with friction welding, see our video tutorial here.

For assembly, check out the graphic showing an exploded view and the names of each part:

  • upper lid;
  • acrylic layer;
  • lower lid;
  • rotor
  • upper platform;
  • containment platform;
  • microswitch plunger;
  • motor mount;
  • case;
  • feet;

It is self-explanatory but just incase you get lost, we have detailed explanations below.

Cutting Acrylic:

We bought a large sheet of 2mm thick acrylic and used a box cutter to very patiently and repeatedly score it until either cutting through or cutting through just enough to snap off a 98x98mm square. This takes practice and lots of patience. Also it requires maximum safety considerations because the cutter can (and will) slip on the acrylic. Take your time, watch your fingers, and do not press too hard.

Weld or Glue:

  1. All of this is illustrated in the video here. There are 4 feet that need to be attached to the bottom of the main case. 2 of these feet will have bolts pass through them and into the legs of the upper platform.
  2. Put the M3 x 10mm bolts in through the feet before welding/gluing to make sure they are lined up properly.
  3. Weld or glue M3 nuts into the ends of the upper platform's legs.
  4. Weld or glue M3 nuts into the inner openings of the hinges on the back of the case.
  5. Weld or glue the acrylic layer in between the upper lid and lower lids;

Assembly:

  1. Use 4 M3 nuts and bolts to secure the motor mount in place;
  2. Place your electronics into the case. Use the photos for guidance if you're not sure;
  3. Insert the microswitch plunger upward through the bottom of the containment platform. The top of the plunger should be poking through the top of the containment platform. Grab it and hold it while placing the containment platform into the main case. Make sure the edge it rests on is clear of wires;
  4. Insert the upper platform's legs into the openings in the containment platform. Make sure there are no wires beneath where the legs will rest and make sure the microswitch plunger opening on the upper platform lines up with the opening on the containment platform;
  5. Insert bolts into the bottom of the case into the nuts located in the legs of the upper platform;
  6. The rotor is press fit. Press it onto the shaft of the motor and push it down until the top of the rotor is flush with the top of the upper platform. If the rotor doesn't fit, use small jeweller's screwdrivers or other small tools to open the rotor's opening up a little. If it is too loose, use a small dab of hot glue before pressing it down;
  7. Fit the upper/lower lid assembly's hinges with the case's hinges. Use (x2) M3 x 30mm bolts to secure it into place. Sometimes the hinges are very tight and you need to move them up and down repeatedly until they smooth out;
  8. When the lid closes you should hear a distinct click from the microswitch. If not, something isn't lined up and you need to backtrack and find out why. We hot glued our microswitch in place to prevent it from sliding out of place;
  9. The remaining M3 x 30mm bolt is used to hold the lid closed by placing it through the latch located on the front of the case;

Step 2: Operation, Safety, Uses

Operation

Useage is covered in our video tutorial here.

  1. Plug your 12V DC adapter into the power barrel adapter in the back of the case;
  2. Flip the rocker switch to on;
  3. Close the lid and hold it closed. This triggers the microswitch, closes the circuit and causes the rotor to spin;
  4. Release the lid and the microswitch will disengage. Wait for the rotor to stop spinning before fully opening the lid.
  5. When loading the rotor with test tubes ensure that the test tubes do not make contact with the walls of the centrifuge;
  6. When loading the rotor with test tubes, ensure that the load is balanced. Place tubes opposite one another and with relatively the same amount of contents in them. Lopsided rotors will create extreme vibrations damaging your centrifuge.

!!!SAFETY!!!

Build and operate this centrifuge at your own risk. We have used this centrifuge and the two versions before it extensively. By always ensuring the lid is closed and that the rotor has come to a complete stop before opening the lid, we have never had an accident.

Test tubes can open during operation and spray their contents in all directions. This can get into the electronics or on you. Make sure not to use anything hazardous.

This centrifuge is designed for basic DNA extraction and spinning things no more hazardous than dish soap and rubbing alcohol.

Uses

We use our series of centrifuges for basic DNA extraction. The protocol we used can be found on our partner website here.

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