TMT Polished Roundel Inspection - On-site inspection of TMT roundel produced by Coherent Inc. in June 2021. Within an inspection tent pavilion, Glen Cole, leading TMT optics fabrication, and Coherent inspector, verify the surface of a finished roundel - Image credit: TMT International Observatory
Pasadena, CA – June 2021 – The production of TMT’s primary mirrors in North America is progressing very well. Several polished glass-ceramic roundels are currently in production at the Coherent manufacturing facilities; three were recently finished and shipped to the TMT storage facility in the Bay Area.
TMT M1 polished roundel produced at Coherent facility in California – June 2021. Another finished roundel for TMT’s primary mirror is carefully prepared for packing and shipping. Image credit: TMT International Observatory
TMT optics and quality assurance engineers, Glen Cole and Scott Shankle, visited the Coherent production facility to complete the source inspections. Prior to this trip, the quality safety and data packages were reviewed and approved so TMT engineers could focus their visit on inspecting each roundel and verifying the cosmetics of the glass surface. The inspection concurred that the surface quality of the newly delivered three roundels meets the technical specifications.
“The roundels are mainstream parts in making TMT’s primary mirrors,” says Cole, TMT lead optical fabrication engineer. “We are excited to see really good, positive progress and have now entered production mode with Coherent.”
While Coherent’s roundel production process is well established, it is also being continually optimized to reach a steady production rate.
Following inspections, each accepted roundel was sealed up in a giant plastic bag and installed in a wooden crate to protect them from dust, humidity and shocks.
Packing TMT finished roundel at Coherent facility, in June 2021 - Held by the three suction cup lifters of a crane, the TMT polished roundel is carefully placed in a shipping crate and sealed inside a large optical tissue paper for protection - Image credit: TMT International Observatory
The three crates have been safely shipped to TMT’s storage facility in Fremont, California, where they joined two other polished roundels that were transferred earlier this spring.
Storage of TMT polished roundels - A total of five accepted and completed roundels produced by Coherent are stacked at the TMT storage facility in Fremont, CA, June 2021 - Image credit: TMT International Observatory
Six new additional blanks, made of CLEARCERAM-Z ultra-low expansion glass-ceramic developed by OHARA Inc., have also arrived at Coherent to start their polishing process. This complex process consists of a series of 14 separate steps during which the roundel is polished at least 5 times, and takes approximately one month to complete.
Each blank and roundel, securely packed in individual crates, are carefully moved around TMT’s storage facility. All shipments must conform to TMT specifications and are witnessed by TMT Quality Assurance experts.
TMT Mirror Shipping activity in the Bay Area - Six TMT Primary Mirror blanks arrive at Coherent and are ready to enter the shop, June 10, 2021 - Image credit: TMT International Observatory
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