University of Hawaii Institute for Astronomy telescopes

Out-of-This-World Accuracy for Precision Milling

June 14, 2012
Machining center produces one-off diffraction gratings for remote sensing instruments used with telescopes and other research instruments

There is a cosmic irony to the machining activity in the laboratories at the University of Hawaii’s Maikalani Institute for Astronomy (IFA) Advanced Technology Research Center. The staff there have their eyes are on the stars, but their hands are at work machining components for instruments developed there to evaluate happenings in deep space.

University of Hawaii Institute for Astronomy telescopes are able to see the solar system and into deep space with greater clarity than at any other location on the planet, according to Dr. Ritter.

This is no typical machine shop, in its lush setting with views of the surf and the skies on the island of Maui, where machinists are just as concerned with the speed of light, dark energy, and the power of space telescopes as they are with speeds/feeds, tooling life, and material hardness.

The Maikalani IFA provides laboratory workspace for physicists and astronomers performing advanced metrology and optical fabrication, novel optics design, optical/infrared sensor development and a creative workspace. “Maikalani” means “the knowledge we gain from the cosmos.” Lab director and physicist Dr. Joe Ritter explained: “At the IFA, our staff and faculty invent, design and build novel instruments for use in state-of-the-art telescopes. Among other technologies, we are working to develop a novel generalized conformal diffraction grating. Gratings are optical components used to split light into component colors for the study of the chemistry of stars.”

Ritter and his assistant John Valliant are also the lab’s machinists. The physicists deploy a Spinner MC650-5A milling machine, equipped with Siemens Sinumerik 840D solution line CNC to produce parts from high-conductivity copper and aluminum 6061-T6 grades, among other alloys.

The Spinner MC650-5A turning center.

Because the IFA’s Spinner is used exclusively for one-off production of precision parts, the search for the right machine focused on equipment that had among the industry’s highest standards of accuracy and precision. The novel conformal gratings under development at the lab are designed with variable pitch and spacing dimensions to correct optical aberrations, and also focus and split infrared light for future deep space spectroscopy instrumentation.

“Accuracy is everything in optics,” Ritter explained. “Most of the machining centers I evaluated were in the +/-25 micron (~0.001 in.) range for accuracy. We settled on a 3+2 axis machine with 100 nanometer precision scales with interferometric remapping on the 840D sl CNC.

“Because we do experimental fabrication work and optics typically need to be made to micron level tolerances, it was imperative to have a feedback control on the machine tool with a known accuracy and predictable degrees of variation,” he continued. For example, though not suitable for visible light, the optics Ritter discussed required accuracies of a few microns — good enough for infrared optics. Other technologies that Ritter and his IFA colleagues are developed include novel photonic meta-materials for future space telescopes, intended for studying exoplanets and the evolution of our universe.

Ritter recalled that IFA faced the standard challenge for educational and research institutions, looking for advanced machinery … budget constraints. In this case, though, he said the lab was fortunate to have been alerted about a Spinner demo machine available from Lois Hill and Robert “Mac” McPherson of MacHill Machinery. During the purchase and commissioning, Ritter added, “The Spinner technician who trained us, Siegfried Jungk, was exceptionally talented and particularly knowledgeable and helpful.”

He also reported that the Siemens ShopMill HMI software included with the CNC package was “an easy-to-use program for getting the multi-axis machining up and running for basic drilling and facing.”

Sample parts produced on the IFA’s Spinner machine, mostly copper and aluminum, include many that become conformal diffraction gratings for use on highly sensitive instruments. “Gratings are optical components used to split light into component colors for the study of the chemistry of stars,” physicist and lab director Dr. Joe Ritter explained.

Though Ritter and his colleague John Valliant are frequently the smartest guys in any room, they are not machinists by trade. So, they use both Shopmill and CAD/CAM programs like Mastercam with the specialized G-code generator and post-processor needed to create precision toolpaths, and then run them directly on the mill to begin cutting quickly — which is necessary in their world of customized parts.

“For some optics, the millions of coordinates we use for every workpiece are pushing the control to the limit, but it responds well. Plus, the teach-in functionality of the Sinumerik 840D sl CNC and its software package keep us running very efficiently,” according to Valliant, who worked in the lab as a University of Hawaii-Maui undergraduate and has learned CNC machining on the go. In an environment where 0.1 of a wavelength of light is the desired target for accuracy, this is no small achievement. “Once you’re comfortable with this machine and the control, the process is very intuitive,” Valliant added.

Dr. Ritter, who frequently tests the design boundaries for novel orbital space telescopes, noted that the state of Hawaii and the island of Maui in particular, have some of the best conditions on Earth for nighttime telescopic observation, as well as the best in the world for daytime solar viewing. Soon, the National Science Foundation will build the world’s largest solar telescope on Maui.

In fact, the island paradise is a little known hotbed of technology development. In addition to solar research and deep space observations, the Institute for Astronomy partners with many nations on scientific training programs.

Dr. Joe Ritter and John Valliant, who operate the Spinner machine at the lab.

Currently, the Institute is engaged in developing technology to make other new scientific discoveries possible. These include the largest camera on earth; new, high-contrast off-axis telescopes; instruments using electronic cameras and spectrographs for the telescopes at Mauna Kea, Haleakala and, in Chile; detectors such as ultra-sensitive mega-pixel infra-red CCD arrays; plus adaptive optics to help overcome the image blurring caused by Earth’s atmosphere. Knowledge gained from the cosmos depends on maintaining Hawaii’s dark skies.

Another initiative by Ritter, who chairs the Maui County Outdoor Lighting Committee, includes developing novel, efficient low-light pollution outdoor and street lighting to preserve endangered species sea turtles and migrating seabirds, as well as to preserve dark skies for astronomy.

Mac McPherson, the Spinner machine dealer and importer for North America, added, “We do considerable business with academics and it’s always challenging, owing to the unique nature of their machining needs. In this case, an optic grid pattern with high accuracy was the biggest hurdle. We were able to supply the Spinner demo machine within budget and with the proper tooling included. The lab actually built their own custom fixturing for their work, and Siemens helped to develop a special post-processor program.”

“Na Kilo Hoku” means “the watchers of the stars,” and the instrument components made here certainly help them do just that — and also to gain knowledge from the cosmos for us all.