Delivery Shapes, Dimensions, and Tolerances

Zerodur can be supplied in the form of disks, rectangular blocks, prisms, rods, and cut pieces. Thick disks which are self-supporting can be produced with up to more than 4 m in diameter and with volumes of about 8 m (equivalent to 20 metric t). Thin menisci which are not self-supporting can also be produced up to masses of about 20 t the largest sizes produced so far were the 8.2 m menisci for the Very Large Telescope of the European Southern Observatory see Sect. 4.3.1. 

In some cases, tighter tolerances are required by optical figuring shops. Zerodur thin menisci or piano-spherical blanks can also be supplied in near net shape. Net shaping means linear dimension tolerances of 0.2 mm or smaller. The spherical grinding of such net shaped blanks leads to profile tolerance zones ranging from 0.05 to 0.40 mm P-V. These tolerances are achieved not only for blanks of 1.0 m in diameter but also for thin menisci of 8.2 m in diameter. 

All basic geometric shapes can be obtained by precision machining using modern CNC processing equipment and high-performance diamond tools. 

These shapes also include certain hght-weight structures which combine the requirements of high stiffness with low weight and low heat capacity. 

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