Chapter R: R RWMA

R

Ra

Abbreviation for roughness average.

R&D

Acronym for research and development.

rack

(1) A gear whose teeth lie in a straight line instead of a circle. A worm has a pitch plane lying parallel to the center lines of worm and gear touching the pitch cylinder of the worm wheel; (2) a metal bar cut with gear teeth so that a circular gear can mesh with it to convert rotary into reciprocating motion or vice versa; (3) a gear with teeth spaced along a straight line, and suitable for straightline motion. A basic rack is one that is adopted as the basis of a system of interchangeable gears.

radial drill

A drilling machine for large, heavy work. It has a movable arm containing the spindle that can be set at different distances from the post or column and rotated around it, offering great flexibility in dealing with massive or cumbersome workpieces.

radian

Also called a rad. An arc of a circle, equal in length to the radius; an angle at the center of a circle, formed by 2 radii cutting off such an arc. One rad = 180 / ? = 57.29578 . The SI unit for plane angles.

radius and fillet gage

It consists of a holder containing a series of thin stainless steel or stainless steel blades or "leaves" of varying size, somewhat like a pocket knife. Each thin steel blade has the corresponding radius accurately formed in it. Used for checking the size and...