A ruling engine that has produced gratings of larger size and greater power than hitherto available is described, as are the characteristics of gratings and echelles ruled by it. This MIT C engine, now fitted to rule blanks of sizes up to 450 × 650 × 125 mm weighing up to several hundred kg, was constructed by applying interferometric translation and mirror-parallelism control to a modified Moore No. 4 Universal Measuring Machine without Y or Z motion. To the base of this were added monorail diamond ways, two diamond carriages and lifters, special end-thrust bearings, mountings for lasers, and a diamond drive with heavy flywheels. Developed by use of the results of experience with our B and A engines, the new machine shows greater mechanical and thermal stability than either, and has produced well-blazed echelles and gratings of superior quality up to the 580-mm (23 in.) diagonal size, at spacings between 632 and 31.6 grooves/mm. The total length of groove per grating is limited at present to about 80 km by diamond wear, and the speed of ruling by internal vibrations and electronic noise. Ghost, satellite, and scatter intensities are at the low levels characteristic of B-engine gratings.
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