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RAKE ANGLE. The angle between the face of the tool or cutter and a plane through the cutting edge. It is the angle on the rake face of the tool where the chip slides.
REAMERS. Multiedged cutting tools, mainly used for two purposes: to bring holes to a more exact size, and to improve the finish of an existing hole by machining a small amount from its surface. No special machines are built especially for reaming. It is usually done on drilling or milling machines. The principal types of reamers are: hand, machine, shell, expansion, and adjustable reamers.
REAMING. The machining operation where reamers are used to improve on a drilled hole (See REAMERS.)
RESIDUAL STRESSES. Stresses that remain within a workpiece after it has been worked on (machined, formed, or heat treated) and all external forces have been removed.
REVERSAL PRINCIPLE. A technique which obtains measurement twice with opposite setups in order to eliminate the error due to the arbor or the instrument.
REVOLUTIONS PER MINUTE (RPM). The number of rotations of the tool or workpiece per minute.
ROCKWELL HARDNESS TESTER. Hardness measuring method in which the hardness value of the test piece is a function of the indentation by an indentor under static load.
ROOT MEAN SQUARE (RMS). A mathematical measure of the average roughness of a surface.
ROUGHING. A machining operation intended for heavy metal removal. Usually followed by finish machining to obtain the required dimension and surface finish.
ROUGHNESS. Surface finish characterized by sharp, closely spaced high and low spots.
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