Pipettes are prolific in laboratories everywhere and used to transfer variable amounts of liquid. Professional tools are calibrated and have dials that allow the user to set the volume. The following instructions are the result of an experiment to develop 3D printable and low cost alternatives to standard lab tools, such as the pipette. This simpler version uses a straw and allows the user to adjust volume using two limit thumb nuts. It should be very useful around any wet lab and works nicely with a relatively high range of possible volume settings. You can calibrate the volume but it is generally only good for low precision work. With the exception of a balloon or rubber glove, spring, straw, and some tape, all the parts are 3D printable without support using a variety of low cost printers. This is a very nice example of alternative lab tools and I hope will contribute to further work in the area. You can also find this model and some user remixes on thingiverse: http://www.thingiverse.com/thing:64977
Step 1: Get Everything Together and 3D Print the Pipette Components
Print the upper body, lower body, plunger, and two thumb gears using a 3D printer, the STL files are attached. I printed all the pieces on a Makerbot Replicator 2 at 0.1mm with 15% fill and 100% fill for the plunger.
You will need a spring, which I got from a kids Pez dispenser for its form factor. The balloon membrane or rubber glove is elastic so you may get away without the spring but it is nicer to have it. You also need some tape to seal the gap, and a straw. It is designed for standard straw diameter (which also works with the standard pipette tip) but I can upload others if there is demand, let me know.
Step 2: Make the Membrane
The pipette uses a membrane which is displaced by the plunger and changes the volume in the cavity below allowing for the droplet to be drawn and ejected. Depending on your printer you may need to put some sealant in the cavity and possibly around the membrane, some people have used glue which seems to work fine.
Step 3: Press Together Two Halves.
Hard press the two halves together until fully joined.
Step 4: Cut Away Any Overhang
Use scissors to cut away excess material.
Step 5: Seal the Gap With Tape
Tape worked best for me. I used it to seal the gap and electrical tape has held for months.
Step 6: Insert and Seal Straw
Insert a standard size straw, you may need to add some glue at the interface between the straw and the plastic to seal any gaps. If your pipette does not work as demonstrated in the next step, you may have to go back and make sure there are no leaks either in the cavity with the membrane or at the straw.
Step 7: Test and Calibrate
You can calibrate the pipette using a variety of methods, for example with a balance. I will let you figure out what is best for you. You can see some of the results I have been getting using this tool.