This Instructable presents a design for a 3D-printed centrifuge. It also contains discussion of the design, and centrifuge design in general.
A couple of months ago, I read an article on Popular Science about one of their writers, Paul Adams, who was lucky enough to tour the Modernist Cuisine test kitchen. Among other really awesome equipment the Modern Cuisine chefs/mad food scientists have at their disposal is an $8000 Sorvall RC-5C Plus High-Performance Centrifuge, which they use for culinary purposes. It turns out that when ordinary food items are subjected to extreme centripetal forces in a centrifuge, some interesting things can happen. Paul Adams did a follow-up article demonstrating how he used a small centrifuge to separate the solid and liquid components of pea puree and made pea butter.
After reading that article, I got really interested in what other foods could be put into a centrifuge to produce strange and enticing new flavors and textures. I started scouring the web for other cool examples of molecular gastronomy dishes made by spinning food in a centrifuge. The pea butter in Paul Adam's article certainly looks very tasty, but I wanted to see more than just a green spread for toast. Unfortunately, there are very, very few other examples of centrifuge recipes to be found; even after extensive searching, all I was able to find were a few random forum posts vaguely describing centrifuge experiments. I was not even able to find any pictures (other than more pictures of pea butter).
So, decided to get a centrifuge for myself and start hacking food. But there was a problem: centrifuges are quite expensive. Even low-powered bench-top models cost over $200. Good-quality bench-top models can cost twice that. Since I didn't want to blow my entire quadcopter fund on a centrifuge, I set about designing my own centrifuge. This Instructable presents that design and a discussion of the ongoing process of formulating and refining it.
So far, the design only exists virtually. Unfortunately, I do not own a 3D printer and creating multiple developmental prototypes, and eventually a finished product, using services like Ponoko would be both extremely expensive and extremely slow. That is not meant to be a criticism of Ponoko, I like their service a lot and I have used it for several projects in the past, it is just not ideal for creating multiple prototypes. Over the summer, when school is out and I have more time to work, I may get a membership to a local hackerspace called Sector 67 where I would have access to a MakerBot Thing-o-matic and I could begin making physical prototypes of the centrifuge. I will make another Instructable once I have a finished device to document the physical build process and some recipes.
In the meantime, if you are interested in making your own 3D printed centrifuge, you are welcome to use the designs in this Instructable either wholesale, in parts, or by creating your own derivative designs.
Instructable Table of Contents
Step 1: Background and General Design Considerations
Step 2: General Safety Considerations and Features
Step 3: Rough Calculation of Applied Centripetal Force and Sample Tangential Speed
Step 4: Non-3D Printed Materials
Step 5: 3D-Printed Parts
Step 6: Plexiglass Cutting Patterns
Step 7: Centrifuge Drivetrain
Step 8: Rotor
Step 9: Safety Enclosure
Step 10: Virtual Testing and Simulation
Step 1: Background and General Design Considerations
Centrifuges: A Basic Introduction
From the Wikipedia page on centrifuges, "a centrifuge is a piece of equipment... that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration causes denser substances to separate out along the radial direction (the bottom of the tube). By the same token lighter objects will tend to move to the top (of the tube; in the rotating picture, move to the centre)."
Basically, a centrifuge is a device that spins a tube containing a liquid sample about a central axis. This rotation causes the sample to be subjected to a centripetal force. Since the tubes are oriented radially with the top of the tube towards the axis, the centripetal force simulates an extreme gravitational force on the tube. It is as if you stood the tube on end in a laboratory (or kitchen) on Jupiter (only the centrifuge actually exerts much, much more force than Jupiter's gravitational pull would). This increased force causes heavier parts of the sample, like suspended solids and fats to sink to the bottom of the tube, while lighter components, like liquids, float to the top.
Centrifuges are typically used in chemistry, biology, and biochemistry for isolating and separating suspensions. However, they have recently begun seeing use in molecular gastronomy, a field of food science that seeks to utilize scientific principles and techniques in the preparation of food. Little documentation exists as yet, however, of recipes for food prepared with centrifuges. It is the goal of this Instructable to begin changing that.
The overall goal of this project is to create a centrifuge capable of spinning up to eight 15mL samples at high enough speeds to achieve separation of the liquid, solid, and semi-solid portions of the sample. In addition to this function, the centrifuge must
- be safe both during normal use and in the case of failure.
- be easy to use.
- be sanitary as it could be used in the preparation of food for human consumption.
- be aesthetically pleasing and customizable in order to fit in with the decor of a kitchen.
Parts of the Centrifuge
More detail is given on the steps dedicated to each system.
Drivetrain (Step 5): The drivetrain is the portion of the centrifuge that interfaces with a drive motor and transfer's the motor's torque to the rotor. The drivetrain must be strong enough to withstand rotational speeds as high as the maximum of which the drive motor is capable, plus a generous margin of safety.
Rotor (Step 6): The rotor is the portion of the centrifuge that rotates and secures the sample-containing tubes during operation. The rotor will be capable of holding a maximum of eight 15mL tubes. Tubes are loaded into the rotor in pivoting brackets so that, when the centrifuge is at rest, the tubes hang vertically, and during operation, the tubes lie radially, parallel to the direction of the centripetal force exerted upon them. The rotor must be strong enough to hold the sample tubes under centripetal forces generated at the maximum rotational speed of the centrifuge, plus a generous margin of safety.
Safety Enclosure (Step 7): The safety enclosure contains all the moving parts of the centrifuge, save the drive motor. The enclosure is designed to do two things. First, the enclosure prevents any foreign object from entering the centrifuge during operation. Second, the enclosure is a shield designed to prevent any part of the centrifuge, or the sample tubes, from being ejected from the machine in the case of failure. The enclosure is designed to protect the centrifuge operator, and anything else that could suffer damage from a mechanical failure of the centrifuge.
Sources of Inspiration
As mentioned in the introduction to this Instructable, the primary source of inspiration for this project was an article in Popular Science by Paul Adams. Mr. Adams wrote a great demonstration piece showing how a centrifuge could be used in food preparation, specifically by making pea butter out of the fat separated from a pea puree. It was this article that piqued by interest in experimenting with food in a centrifuge. However, because centrifuges are quite expensive, I got to work designing my own.
Before I started the project, I had heard a story about how a 3D printer was used to produce a small centrifuge attachment for a Dremel rotary tool. The project, called the DremelFuge, is a fantastic proof-of-concept that 3D printing can indeed by used to make a centrifuge, however, there are some serious oversights in the design, especially relating to safety. The DremelFuge has no safety enclosure whatsoever. If one of the sample tubes were to detach from the rotor during operation, it could cause serious, even life-threatening injuries to the operator, or others. Even operating at the minimum rotational speed discussed on the Thingiverse page, 3000 rpm, the tubes have a tangential speed over 70 mph, which, even though the sample tubes are small and light, is fast enough to cause bodily harm. The truly frightening bit though is the discussion of operating the DremelFuge at a much faster, 30,000 rpm. With this rotational speed, the sample tubes have a tangential velocity of approximately 715 mph! This speed is quite close to the speed of sound and the sample tubes traveling at this speed would have more than enough kinetic energy to cause severe damage to whatever they might hit, including a human body.
The last source of inspiration for the centrifuge design in this Instructable came from simply searching the web for other examples of homemade centrifuges. A simple image search on Google will return many examples of homemade centrifuges. Some are better than others, but they all offer ideas for the many different ways a centrifuge could be designed from scratch.