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HARD TURNING. A turning process using very hard cutting tools, such as CBN or ceramics, to turn directly hardened materials. This process now can turn steel with hardness up to 65 Rc, and has a competitive edge over grinding. Generally speaking, it produces better surface integrity and requires much less specific energy than does grinding.
HEADSTOCK (IN LATHES). The headstock of the lathe is mounted at the left-hand end of the machine. It is the unit which turns the workpiece. It contains the spindle and series of gears or pulleys by which the spindle is rotated at various speeds.
HELIX ANGLE (DRILLS). The angle between a line tangent to the land of the flute and the axis of rotation at their point of intersection.
HELIX ANGLE (MILLING CUTTERS). The angle between a line tangent to a point on the helical tooth and the axis of the cutter measured at their point of intersection.
HETERODYNE INTERFEROMETER. A device using two frequency laser beams to generate fringe patterns for determining machine accuracy such as linear displacement, angular rotation, straitness, squareness, and parallelism. Resolution up to one hundredth of the
laser beam wavelength is achievable.
HIGH EFFICIENCY MACHINING RANGE. The range of cutting speed which is bounded by the speed for minimum machining cost and the speed for maximum production rate.
HIGH SPEED MACHINING. The term "high speed" is relative and is compared with the speed of conventional machining processes. As a general guide, an approximate range of speeds may be defined as follows:
High Speed - 2,000 - 6,000 ft./min.
Very High Speed - 6,000 - 60,000 ft./min.
Ultrahigh Speed - Greater than 18,000 ft./min.
High speed machining should be considered basically for situations in which cutting time is a significant portion of floor time of the operation. The workpiece materials used include aluminum alloys.
HIGH SPEED STEEL (HSS). Conventional material for cutting tools. It is mainly made of high carbon steel alloyed mainly with tungsten and molybdnum.
HONING. Rotational metal removal process using combined rotational and reciprocating motion of bar-shaped abrasive tools mainly for internal cylinders to improve finish and dimensional accuracy.
HORIZONTAL SURFACE GRINDING. The generation of finished flat surfaces by mounting workpieces on a traversing work table below a grinding wheel that rotates about a horizontal axis.
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