INTERNATIONAL STANDARDS
ISO 3290 - THIRD EDITION - 2001/12/01

FORM AND SURFACE ROUGHNESS TOLERANCES

SORTING TOLERANCES AND GAUGES

TERMS AND DEFINITIONS

Nominal ball diameter - D_w: diameter value which is used for the general identification of a ball size.

Single ball diameter - D_ws: distance between two parallel planes tangential to the actual surface of a ball.

Mean ball diameter - D_wm: arithmetical mean of the largest and the smallest of the single diameters of a ball.

Variation of ball diameter - V_Dws: difference between the largest and the smallest of the single diameters of a ball.

Surface irregularities and form parameters: various types of deviation from the perfect spherical ball surface, uniformly distributed and repeated around the ball surface. NOTE: the deviations to which limits can be attributed are: deviation from spherical form -waviness - surface roughness.

Deviation from spherical form - t_Dw: greatest radial distance, in any equatorial plane, between the smallest circumscribed sphere and the greatest inscribed sphere, with their centres common to the least square sphere centre. NOTE: information about the measurement of this deviation is given in annex A.

Waviness: surface irregularities of random or periodical deviation from the ideal spherical form. NOTE: it is recommended that wavi­ness be evaluated as velocity amplitude In practice, the waviness components are separated from the real surface by a waviness analyser (filters).

Surface roughness: surface irregularities with relatively small spacings, which usually include irregularities resulting from the method of manufacture being used and/or others influences. NOTE: these irregularities are considered within the limits that are conventionally defined, e. g., within the limits of the sampling length.

Surface defect: element, irregularity or group of elements and irregularities of the real surface, unintentionally or accintally caused during manufacture, storage, handling or use of the surface. NOTE: these types of element or irregularity differ considerably from those consulting the surface roughness and should not be considered during the measurement of the surface roughness (see 4.2, note 2). Surface defects (and their limits) are not specified in this International Standard.

Ball lot: defines quantity of balls manufactured under conditions presumed uniform and which is considered as an entity.

Mean diameter of ball lot - D_wmL: arithmetical mean of the mean diameters of the largest ball and the smallest ball in a ball lot.

Variation of ball lot diameter - V_dwL: difference between the mean diameters of the largest ball and the smallest ball in a ball lot.

Ball grade - G: specific combination of dimensional, form, surface roughness and sorting tolerances for balls. NOTE: ball grade is identified by the letter G and a number.

Ball gauge - S: amount by which the mean diameter of a ball lot should differ from the nominal ball diameter, this amount being one of an established series. NOTE: 1 each ball gauge is a whole multiple of the ball gauge interval established for the ball grade in que­stion (see table 3 and annex B). NOTE 2: a ball gauge, in combination with the ball grade and nominal diameter, should be conside­red as the most exact ball size specification to be used by a customer for ordering purposes.

Deviation of a ball lot from ball gauge - D_S: difference between the mean diameter of a ball lot and the sum of the nominal ball diameter and the ball gauge D_S = D_wmL - (D_w+S). See table 3 and annex B.

Ball subgauge: amount of an established series of amounts, which is the nearest to the actual deviation from the ball gauge of a ball lot. NOTE 1: each ball subgauge is a whole multiple of the ball subgauge interval established for the ball grade in question (see table 3 and annex B). NOTE 2: the ball subgauge, in combination with the nominal ball diameter and the ball gauge, is used by ball manufacturers to denote the mean diameter of a ball lot and should not be used by customers for ordering purposes.

Hardness: measure of resistance to penetration as determined by specific methods.

REQUIREMENTS

Ball size: the preferred nominal ball diameters are given in Table 1. Where applicable, the corresponding inch sizes are given for reference purposes only.

Quality of geometry and surface: requirements for: variation of ball diameter, see table 2 - deviation from spherical form, see table 2 -waviness, see note 1 - surface roughness, see table 2 - surface appearance and defects, see note 2. Measurement of surface rough­ness shall be made in accordance with ISO 4288. NOTE 1: limits and measuring methods for waviness should be agreed upon between customer and supplier, NOTE 2: surface appearance characteristics, local defects, scratches and the like are subject to agreement between customer and supplier.

Sorting accuracy and ball gauges: Table 3 comprises the applicable values for: variation of ball lot diameter - gauge interval - prefer­red gauges - subgauge interval - subgauges.

Hardness: hardness values and the measuring method shall be agreed upon between customer and supplier.

METHOD FOR ASSESSMENT OF DEVIATION FROM SPHERICAL FORM

The measurement of deviation from the spherical form of balls shall be carried out by measurement of roundness deviation in a required number of single equatorial planes. The evaluation of roundness in a single equatorial plane may be carried out by calculation from the least square centre. The greatest radial distance in any single equatorial plane is assumed to be the deviation from spherical form. Roundness deviation is measured in three equatorial planes 90° to each other. For a detailed description of methods for the assessment of deviation from roundness see ISO 4291.

ILLUSTRATION OF GAUGES AND SORTING PRINCIPLES

Gauge and subgauge: Figure B. 1 shows an example of gauge and subgauge for grade G5 balls:

a - ubgauge interval b - Subgauge scale used by manufacturer c - Gauge sea e used by customer d - Gauge interval e - Nominal ball diameter, Dw

LOT AND GAUGE DEVIATION

1 - Smallest ball in the lot 2 - Lot 3 - Largest ball in the lot 4 - Lot with smallest DwmL to be referred to gauge S 5 - Lot with largest DwmL to be referred to gauge S a - Variation of ball lot diameter, VDwL b - Variation of ball diameter, VDws c - Mean diameter of ball lot, DwmL d - Subgauge scale e - Gauge scale f - Deviation of a ball lot from ball gauge, DS g - Subgauge to which the lot is referred h - Gauge S i - Range of mean diameter of ball lot for ball gauge S.