Ling Lu, a postdoc in the Department of Physics, had an idea for a photonic crystal that theoretically could capture the Weyl particle, the massless solution to the celebrated Dirac equation first predicted by physicist Hermann Weyl in 1929.
Although thousands of theoretical papers and books have been written about the Weyl particle, its existence had not been confirmed — but Lu had a plan for its detection.
Building on previous research, Lu calculated the precise measurements for the photonic crystal in the shape of a three-dimensional honeycomb-like double gyroid. Then, with a computer-aided design (CAD) drawing in hand, Lu spent half a year searching for a company that was willing and able to make such a photonic crystal, looking everywhere from Massachusetts to China.
Again and again, companies would take one look at Lu’s CAD drawing and turn him away: The demands of time, labor, and precision of the photonic crystal were too high for a for-profit company to meet for a price Lu could pay.
But, in the end, Lu wouldn’t have to go very far: The MIT Central Machine Shop would work with Lu to turn his CAD drawing into a reality.
Solutions for research
Buried in the basement of Building 38, the Central Machine Shop has been the secret to the success of many research projects at the Institute. The shop helps members of the MIT research community with machining projects that span a wide range of size, scope, and complexity. If there is something that can be machined, but doesn’t exist yet, the Central Machine Shop can make it — or will locate and work with an outside shop that can.
Of the 1,200 projects the shop completes every year, many are small and take just a few minutes to finish, such as a bracket for holding microscope specimens. But other projects are far more complex. For instance, the shop fabricated a drug-delivery capsule for researchers in the Department of Chemical Engineering and MIT's Koch Institute for Integrative Cancer Research. The finished capsule was the size of a pill, and required the shop staff to painstakingly machine each tiny, hollow needle that lined the outside of the capsule.
At the other end of the size spectrum, the shop built a series of flumes for Professor Heidi Nepf in the Department of Civil and Environmental Engineering, ranging in size from table-top flumes used for training students that could be broken down and stored away, up to room-length flumes with features such as wave-makers. The shop staff not only had to design a recirculating flume so that it could be moved between a temporary lab and its permanent home, but also discover a mechanism that prevented the sand inside from infiltrating and breaking its motor.
To carry out these projects, the Central Machine Shop is equipped with the basic tools found in any machine shop: mills, lathes, grinders, and welding equipment. But the shop’s staff sets it apart, bringing decades of experience to each job, as well as a great deal of skill, ingenuity, and determination to see projects through to completion.
“Our staff is made up of highly skilled designers, machinists, welders and fabricators, all with their unique skill set,” says shop supervisor Andy Gallant. “This allows us to cover almost anything that is brought our way (within equipment capabilities). The staff are skilled craftsmen who take pride in their work and are all happy to work closely with the MIT community in creating their parts.”
Drawing toward discovery
Transforming Lu’s CAD drawing into a real photonic crystal would prove a true test of the shop staff’s skill, ingenuity and, especially, their patience.
The problem lay in the crystal’s intricate and delicate structure. While one gyroid could be machined with relative ease, Lu’s crystal is composed of two gyroids that do not touch at any point, and yet are interwoven in such a way that they must be constructed together. The 3-D printing machines could easily produce the structure, but not using the high-performance ceramic required. Various 3-D machining tools could theoretically produce the shape precisely enough to produce a Weyl point, but only with so much time and labor as to make the project unfeasible.
But in collaboration with Andy Gallant, the shop’s supervisor, Lu was able to rework his CAD drawing so that the shop could produce the photonic crystal. Lu identified the one possible way he could slice the crystal into stacking slabs, yet preserve the characteristics that were needed to produce the Weyl point. The shop could now produce the crystal through a series of 2-D drilling operations.
Gallant then rebuilt Lu’s new CAD drawing himself, so that he could understand each move of the drill in the process and communicate it to his machinist. They would have to produce at least 20 12-inch-square plates in all, each drilled with a grid of holes. Each hole required three separate drilling operations at different angles, followed by additional finishing work. Each plate would require nearly 1,000 operations altogether, each of them perfect.
The process did not go smoothly at first. The high-performance ceramic was so brittle, either the plate would shatter or the drill would break. Lu first worked with his supplier to figure out that shortening the cure time would soften the plates enough to drill, and then Lu worked with the Central Machine Shop to test plates of different cure levels to find the right balance of performance and pliability. Once the shop started producing complete plates with the modified material, Lu took each plate back to the lab to test it, and then work with the shop to retool the design.
The shop would drill about 40 perfect plates over the course of a year before Lu finally had a working photonic crystal. But the long effort was well worth it: Lu could run the experiment that would at last detect the Weyl point, 86 years after it was first theorized.
“This project was not possible without the Machine Shop’s help,” Lu emphasizes. “It was fully enabled by [the staff's] patience and skill, and by their willingness to work with us for such a long period of time.”
Making ideas happen
The Central Machine Shop started life as the machine shop for the Laboratory of Nuclear Science (LNS). Continuing under LNS management, the shop opened its doors to all members of the MIT community, whether they are a student, staff member, postdoc, or faculty member. For a fee based on hours worked, shop personnel will work in consultation with shop users from start to finish, beginning with a rough idea or sketch, through the refinement of the design, to the completion of a finished, working product.
“One of the things that makes the MIT Central Machine Shop unique is the ability of the machine shop staff to work closely with the students or customers to make sure that all the parts are made correctly,” Gallant says. “If we have any questions, they can come right down and discuss the issues directly with the staff person working on their project. We are also very flexible in making changes to the design on the fly, which happens frequently.”
The Central Machine Shop staff take great pride and enjoyment in guiding MIT community members through this process.
“The best part of my job is taking a blank piece of material and turning into something that someone can use,” said Ernie Johnson, the machinist who worked on Lu’s gyroid slabs. “People really appreciate it when you can take their idea and make it happen for them.”