The mirror of the James Webb Space Telescope (JWST), made of 18 beryllium segments, was manufactured by Axsys of Cullman, Ala., which used Mitsui Seiki USA machines to manufacture the mirrors. The machines ensure volumetric accuracy.
The HMCs Mitsui Seiki built to machine the JWST’s mirror segments combine a massive structure with the ability to position within a few microns anywhere in the machining envelop. Based on Mitsui’s HS6A, Axsys’ machines were modified to fit the task at hand. For example, they use a slightly shorter Z axis travel — 980 mm versus the standard 1000 mm — to accommodate the oversized pallet needed for Axsys’ fixtures. X and Y-axis travels are 2000 and 1500 mm, respectively. Other features include 60-tool ATCs and a laser-based tool monitoring system.
- The JWST Mirror — the heart of the telescope — is made up of 18 beryllium segments, each
1.5 m wide.
- Each mirror billet weighed 700 pounds when loaded into one of the eight Mitsui Seiki HMCs and 28 pounds when machining was complete.
- Each mirror structure required 18 weeks of machining time.
- There are eight different rib thicknesses on the 600-pocket side of the mirror structure ranging from 0.021 inch to 0.2 inch.
- Tolerances for mirror finishing are + 0.0002 inch / – 0.00 inches.
- True position is 0.001 inch from the inside to the outside of the hubs.
- True position is 0.005 inch all the way around the 48-inch bolt hole circle.
- The mirror surface has a specified thickness of 0.098 inch +/- 0.003 inch.
- Tolerances on the 32, 0.250-inch diameter holes on the edge is + 0.0002 inch / – 0.00 inch.
All content excerpted from Manufacturing Engineering’s article: “Stability and Precision: Machining the James Webb Telescope’s Mirrors.”
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