A milling method in which parts are placed in a row parallel to the axis of the cutting tool and are milled simultaneously.

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The total amount, along the axis of rotation, by which the rotation of a cutting tool deviates from a plane.


The axial play of the outer ring in a bearing. The measured maximum possible movement parallel to bearing axis of the inner ring in relation to outer ring.


Any fluid applied to a cutting tool to assist in the cutting operation by cooling, lubricating or other means.


The difference in apparent direction or position of an object when viewed from different points. For bodies of the solar system, parallax is the difference in the direction of the body due to the dis- placement of the observer from the center of the earth, and is called geocentric parallax, varying with the body’s altitude and distance from the earth. The geocentric parallel when a body is in the horizon is called horizontal parallax, as contrasted with the parallax at any altitude, called parallax in altitude. Parallax of the moon is called lunar parallax. In marine navigation it is customary to apply a parallax correction to sextant altitudes of the sun, moon, Venus, and Mars. For stars, parallax is the angle at the star subtended by the semimajor axis of the earth’s orbit and is called heliocentric or stellar parallax, which is too small to be significant as a sextant error.


The total maximum possible movement parallel to bearing axis of inner ring in relation to outer ring in ball or roller bearing assembly. Also called bearing end play.


A load exerted parallel to the axis of the shaft on which the bearing is mounted, also called thrust load.


A reflecting surface having the cross section along the axis in the shape of a parabola. Parallel rays striking the reflector are brought to a focus at a point, or if the source of the rays is placed at the focus, the reflected rays are parallel.


  1. The apparent displacement of a celestial body in the direction of motion of the earth in its orbit caused by the motion of the earth combined with the finite velocity of light. When, in addition to the combined effect of the velocity of light and the motion of the earth, account is taken of the motion of the celestial body in space during the interval that the light is traveling to the earth from the luminous body, as in the case of planets, the phenomenon is termed planetary aberration. The aberration due to the rotation of the earth on its axis is termed diurnal aberration or daily aberration. The aberration due to the revolution of the earth about the sun is termed annual aberration. The aberration due to the motion of the center of mass of the solar system in space is termed secular aberration but is not taken into account in practical astronomy.
  2. The convergence to different foci, by a lens or mirror, of parallel rays of light. In a single lens having spherical surfaces, aberration may be caused by differences in the focal lengths of the various parts of the lens: rays passing through the outer part of the lens come to a focus nearer the lens than do rays passing through its central part. This is termed spherical aberration and, being due to the faulty figure of the lens, is eliminated by correcting that figure. A lens so corrected is called an aplanatic lens. Aberration may also result from differences in the wavelengths of light of different colors: light of the shorter wavelengths (violet end of the spectrum) comes to a focus nearer the lens than light of the longer wavelengths (red end of the spectrum). This is termed chromatic aberration, and is practically eliminated over a moderate range of wavelengths by using a composite lens, called an achromatic lens, composed of parts having different dispersive powers.


A filter in which the inlet and outlet port axes are at right angles, and the filter element axis is parallel to either port axis.


A condition where the shaft axis or center lines of two shafts are parallel but offset from each other.

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