Surface texture is the nature of a surface

Surface texture, also known a Surface finish, is the nature of a surface as defined by the three characteristics of surface roughness, waviness, and lay. It comprises the small local deviations of a surface from the perfectly flat.

Each manufacturing process produces a surface texture

Surface texture is one of the important factors that control friction and transfer layer formation during sliding. Considerable efforts have been made to study the influence of surface texture on friction and wear during sliding conditions.

Each manufacturing process (such as the many kinds of machining) produces a surface texture. The process is usually optimized to ensure that the resulting texture is usable. If necessary, an additional process will be added to modify the initial texture.

Surface discontinuity is an isolated imperfection of the surface like a crack, pore or lap. In general it is not taken into account when assessing deviations of, waviness and roughness.

The different kinds of surface irregularities have different origins in the manufacturing process. In order to control the manufacturing process these kinds must be assessed separately.

The different kinds of surface irregularities often have different effects on the suitability of the surface for its purpose. For example, on raceways of ball bearings, waviness has a great influence on lifetime and noise while roughness has little influence. In order to specify the permissible function-related deviations, the different kinds must be specified separately.

The depths of the irregularities vary in large ranges, between about 0.1 µm (and sometimes smaller) with roughness and about 100 m (and sometimes more) with form deviations. The ratio between spacing and depth of the irregularities also varies greatly. The smallest ratio between spacing and depth occurs with cracks and is in general smaller than 5:1. Whereas the ratio between spacing and depth with form deviations is in general greater than 1000:1. Because of these wide ranges the requirements for measuring devices and for diagrams are quite different. For the assessment of different kinds of the irregularities (deviations) different kinds of measuring instruments with different magnifications and different profile diagrams with different ratios of horizontal to vertical magnifications are used.

The classification of surface irregularities (deviations) as described above is useful, but the definitions of them are rather uncertain, there are no distinct borderlines.

Surface texture is
the nature of a surface

There is another distinction between micro and macro deviations. Macro deviations are those, that can be assessed with usual measuring devices for the assessment of size, form, orientation and location (e.g. dial indicator). Micro deviations are those that are assessed with roughness or waviness measuring instruments. Macro deviations are assessed over the entire feature length; micro deviations are assessed from a representative part of the surface. Also, there is no distinct borderline because sometimes parts of the waviness will contribute to the result of the measured macro deviations and sometimes parts of the form deviations will contribute to the result of the measured micro deviations (waviness).

The following figure gives an idea of the combination (superposition) of the kinds of irregularities (deviations) on a surface (DIN 4760).

Surface deviationThe combination of the kinds of irregularities (deviations) on a surface (DIN 4760) Geometric deviation profle diagram Description Example of origin cutting process (tear chip, shear chip)deformation form blasing, gemmation with galvanizing 1st order: Form 2nd order: Waveness 3rd order: Roughness 4th order: Roughness Superposition error in guidance of machine tool,defection of machine tool or workpiece,error in fxture of workpiece, wraping, wear eccentric fxture,form deviation of toolvibration grooves, form of tool cuttting edge, horizontal and and vertical feed crysallization procces,mordant, galvanizing actual surface crysal sructure Super position of surface deviation (DIN 4760) 5th order: Roughness not presentable 6th order: Roughness not presentable

Lay

Lay is the direction of predominant surface pattern remaining after cutting, grinding, lapping, or other processing.

Lat pattern
Lay pattern is determined by the manufacturing method

The symbols in the following table indicate the lay and direction of lay in relation to the drawing plane containing the surface texture requirement (ISO 1302).


Waviness

Waviness is mostly more or less periodic irregularities of a workpiece surface with spacings greater than the spacings of its roughness (DIN 4774). The ratio between spacing and depth of the waviness is in general between 1000:1 and 100:1. In general more than one wave can be recognized (VDI/VDE 2601). The waviness is assessed from one or more representative parts of the surface.

Waviness is originated during manufacturing process (DIN 4760) due to:

  • eccentric fixture
  • form deviations of the cutter
  • vibrations of the machine tool
  • vibrations of the cutting tool
  • vibrations of the workpiece

Waviness should also be distinguished from flatness, both by its shorter spacing and its characteristic of being typically periodic in nature.

Waviness in bearing balls and bearing races is one of the reasons for vibrations and noise in ball bearings.


Roughness

Roughness is the main component of surface texture, and it is is the deviations in the direction of the normal vector of a real surface from its ideal form. Roughness is periodic or non-periodic irregularities of a workpiece surface with small spacings inherent of the forming process. Roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface. The ratio between spacing and depth of the roughness is in general between 150:1 and 5:1 (VDI/VDE 2601). The roughness is assessed from one or more representative parts of the surface.

Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good symbol for performance of a mechanical component, since irregularities in the surface may lead to cracks or corrosion. Decreasing the roughness of a surface will usually increase its manufacturing costs.

Roughness is originated by the direct effect of the cutting edges on the surface. Other origins are deformations from blasting, gemmation with galvanizing, crystallization, and chemical effects (mordants, corrosion). Roughness ranges down to the crystal structure (DIN 4760).

Surface roughness heights are generally measured in micrometers. The sizes of some familiar items are:

  • Diameter of human hair: 40 to 75 μm
  • Diameter of a spider web strand: 2.5 to 5 μm
  • Diameter of a hydrogen atom: 0.0001 μm
  • Profiles and filters

    The actual surface profile results from the intersection of the actual part surface with a plane perpendicular to this surface.

    The unfiltered primary profile (P-profile) is the actual measured surface profile. Filtering it in accordance with ISO 11562/ISO 16610-21 produces the waviness profile (W-profile) and the roughness profile (R-profile). The variable for determining the limit between waviness and roughness is the cut-off λc.

    Lat pattern
    Surface profile and filtering

    Following ISO 4287, all parameter definitions are valid for both the roughness profile as well as for the primary and waviness profiles. The profile type is identified by the capital letters P, R or W.

    The total height Pt, Wt or Rt of the respective profile type is the maximum height between the highest peak and the deepest valley of the evaluation length profile.

    Roughness parameters

    This is the content for Layout P Tag

    Lat pattern
    Surface profile and filtering

    This is the content for Layout P Tag

    Lat pattern
    Surface profile and filtering

    This is the content for Layout P Tag

    Preferred parameters

    This is the content for Layout P Tag

    Measuring conditions

    This is the content for Layout H3 Tag

    This is the content for Layout P Tag

    Evaluation

    This is the content for Layout P Tag

    Lat pattern
    Surface profile and filtering

    The traverse length (lt) is the total length of the probe movement during the scanning process. It must be greater than the evaluation length ln in order to be able to form the roughness profile with the profile filter. With the exception of Rt and Rmr(c), the roughness parameters are defined within an evaluation length ln, which is determined using an average of five sampling lengths lr.

    The sampling length lr corresponds to the cut-off λc.


    Terms and definitions given in ISO 1302:

    Basic graphical symbol
    (surface texture) graphical symbol indicating that a requirement for surface texture exists.
    Expanded graphical symbol
    (surface texture) expanded basic graphical symbol indicating that material is either to be removed or not removed in order to obtain the specified surface texture.
    Complete graphical symbol
    (surface texture) basic-or expanded graphical symbol expanded in order to facilitate the addition of complementary surface texture requirements.
    Surface texture parameter
    Parameter expressing a micro-geometrical property of a surface. The profile parameters in IS0 4287 are defined for three surface profiles (R-profile , W-profile, and P-profile).
    Surface parameter symbol
    symbol indicating the type of surface texture parameter. NOTE: The parameter symbols consist of letters and numerical values (e.g.   Ra , Ramax , Wz , Wz1max , AR , Rpk , Rpq )

    Graphical symbols to indicate surface texture

    Requirements for surface texture are indicated on technical drawing by several variants of graphical symbols, each having its own significant meaning.

    Basic graphical symol

    The basic graphical symbol shall consist of two straight lines of unequal length inclined at 60" to the line representing the considered surface. The basic graphical symbol should not be used alone (without complementary information).

    If the basic graphical symbol is used with complementary, supplemental information, then no further decision is required as to whether removal of material is necessary for obtaining the specified surface or whether removal of material is not permitted for obtaining the specified surface.

    Basic graphical symbolBasic graphical symbol for surface texture

    Expanded graphical symbols

    Removal of material required

    If removal of material -for example, by machining - is required for obtaining the specified surface, a bar shall be added to the basic graphical symbol. The expanded graphical symbol should not be used alone (without complementary information).

    Removal of material requiredExpanded graphical symbol indicating removal of material required

    Removal of material not permitted

    If removal of material is not permitted for obtaining the specified surface, a circle shall be added to the basic graphical symbol.

    Removal of material not permittedExpanded graphical symbol indicating removal of material not permitted

    Complete graphical symbol

    When complementary requirements for surface texture characteristics have to be indicated, a line shall be added to the longer arm of any of the graphical symbols. Left: any manufacturing process permitted. Midlle: material shall be removed. Right: material shall not be removed

    Complete graphical symbola line shall be added to the longer arm

    For use in the written text of - for example, reports or contracts - the textual indication is as the following:

    APA
    Any process allowed.
    MRR
    Material removal required.
    NMR
    No material removed.

    Graphical symbol for "all surfaces around a workpiece outline"

    When the same surface texture is required on all Surfaces around a workpiece outline (integral features), represented on the drawing by a closed outline of the workpiece, a circle shall be added to the complete graphical symbol. As shown in the following illustration, Surface texture requirement for all six surfaces represented by outline on workpiece.

    all surfaces around symbola circle shall be added to the complete graphical symbol 1 3 4 2 5 6

    Surfaces shall be indicated independently if any ambiguity may arise from the all around indication.

    NOTE:   The outline on the drawing represents the six surfaces shown on the 3D-representation of the workpiece (the front and rear surfaces not included).

    Position of complementary surface texture requirements

    In order to ensure that a surface texture requirement is unambiguous, it may be necessary, in addition to the indication of both a surface texture parameter and its numerical value, to specify additional requirements (e.g. transmission band or sampling length, manufacturing process, surface lay and its orientation and possible machining allowances). It may be necessary to set up requirements for several different surface texture parameters in order that the surface requirements ensure unambiguous functional properties of the surface.

    Positions (a to e)Positions (a to e) for location of complementary requirements d  b a c e

    positions (a to e) are mandatory for location of complementary requirements in the complete graphical symbol.

    Positions a - Single surface texture requirement

    Indicate the surface texture parameter designation, the numerical limit value and the transmission band/sampling length. To avoid misinterpretation, a double space (double blank) shall be inserted between the parameter designation and the limit value.

    Generally, the transmission band or sampling length shall be indicated followed by an oblique stroke (I), fobved by the surface texture parameter designation, followed by its numerical value using one text string.

    EXAMPLE 1:   0,0025-0.81Rz 6.8   (example with transmission band indicated)
    EXAMPLE 2:   -0.81Rz 6,8     (example with only sampling length indicated)

    Especially for the motif method, the transmission band shall be indicated, followed by an oblique stroke (I), followed by the value of the evaluation length, followed by another oblique stroke, followed by the surface texture parameter designation, followed by its numerical value.

    EXAMPLE 3:   0.008-0,51161R 10

    NOTE: Generally, the transmission band is the wavelength range between two defined filters (see ISO 3274 and ISO 11562) and, for the motif method, the wavelength range between two defined limits (see ISO 12085).

    Position a and b together - Two surface texture requirements

    lndicate the first surface texture requirement at position "a". lndicate the second surface texture requirement at position "b". If a third requirement or more is to be indicated, the graphical symbol is to be enlarged accordingly in the vertical direction, to make room for more lines. The position “a” and “b” are to be moved upwards when the symbol is enlarged.

    Position c - Manufacturing method

    lndicate the manufacturing method, treatment, coatings or other requirements for the manufacturing process etc to produce the surface, for example, turned, ground, plated.

    Position d - Surface lay and orientation

    lndicate the symbol of the required surface lay and the orientation, if any, of the surface lay, for example, "=" , "X" , "M" .

    Position e - Machining allowance

    lndicate the required machining allowance. if any, as a numerical value given in millimetres.

    Indication of the surface lay

    The surface lay and direction of the lay emanating from the manufacturing process (e.g. traces left by tools) may be indicated in the complete symbol by using the standard symbols. The indication of surface lay by the defined symbols (e.g. the perpendicularity) is not applicable to textual indications.

    Complete graphical symbola line shall be added to the longer arm Rz1 3.1 Ra 0.7 milled

    The symbols in table 2 indicate the lay and direction of lay in relation to the drawing plane containing the surface texture requirement.

    Indication of the surface lay
    The surface lay may be indicated in the complete symbol by using the standard symbols.

    Position and orientation of graphical symbol and its annotation

    Surface texture requirements shall be indicated only once for a given surface and, if possible, on the same view where the size or location, or both, are indicated and toleranced.

    Unless otherwise specified, the indicated surface texture requirements are applicable for the surface after machining, coating, etc.

    The general rule is that the graphical symbol together with the complementary information shall be oriented so that they are readable from the bottom or right-hand side of the drawing, in accordance with IS0 129-1

    Complete graphical symbola line shall be added to the longer arm Ra 0.7 Rz 1.3 Rp 1.3 Rz 11

    On outline or by reference line and leader line

    The surface texture requirement (graphical symbol) shall touch the surface or be connected to it by means of a referencelleader line terminating in an arrowhead

    As a general rule, the graphical symbol, or the leader line terminating in an arrowhead (or other relevant terminator), shall point at the surface from outside the material of the workpiece - either to the outline (representing the surface) or the extension of it).

    The surface texture requirement may be directly placed on extension lines or be connected to it by a reference/leader line terminating in an arrowhead,

    Surface texture on outlineThe surface texture graphical symbol shall touch the surface or be connected to it by means of a reference/leader line. 32 20 Rz 3.5 turned Rz 6.5 Rz 3.1 milled

    On dimension line in connection with feature-of-size dimension

    If there is no risk of misinterpretation, the surface texture requirement may be indicated in connection with the dimensions given, as shown below.

    surface texture On dimension linesurface texture requirement may be indicated in connection with the dimensions. 60 H7 60 h6 Rz 11 Rz 11

    On tolerance frame for geometrical tolerances

    The surface texture requirement may be placed on top of the tolerance frame for geometrical tolerances (according to IS0 1101).

    On tolerance framesurface texture requirement may be placed on top of the tolerance frame 10 ±0.1 Ra 1.5 Rz 0.6 0.1 0.2 A B

    Cylindrical and prismatic surfaces

    Cylindrical as well as prismatic surfaces may be specified only once if indicated by a centreline and if each prismatic surface has the same surface texture requirement (see Figure 21). However, each prismatic surface shall be indicated separately if different surface textures are required on the individual prismatic surfaces.

    On Cylindrical surfacesCylindrical surfaces may be specified only once Ra 1.1 Rz 6.5 Rz 6.5 Ra 1.4

    Simplified drawing indications of surface texture requirements

    Majority of surfaces having same surface texture requirement

    If the same surface texture is required on the majority of the surfaces of a workpiece, this surface texture requirement should be placed close to the title block of the drawing.

    The general graphical symbol corresponding to this surface texture shall be followed by
    — a basic symbol in parentheses without any other indication ( Figure Left), or
    — the special deviating surface texture requirement or requirements in parentheses (Figure Right), in order to indicate requirements that deviate from the general surface texture requirement.

    Simplified drawing indicationsMajority of surfaces with same required surface texture Rz 6.4 Rz 1.3 Rz 6.4 Rz 1.3 Ra 2.5 Ra 2.5 Rz 6.4 Rz 1.3

    Surface texture requirements that deviate from the general surface texture requirement shall be indicated directly on the drawing in the same view of the particular surfaces in question.

    Common requirements on multiple surfaces

    To avoid the necessity of repeating a complicated indication a number of times, or where space is limited, or if the same surface texture is required on a large number of surfaces of the workpiece, a simplified reference indication may be invoked as follows.

    Common requirements on multiple surfaces

    To avoid the necessity of repeating a complicated indication a number of times, or where space is limited, or if the same surface texture is required on a large number of surfaces of the workpiece, a simplified reference indication may be invoked as follows.

    Indication by graphical symbol with letters

    A simplified reference indication may be used on the surface provided that its meaning is explained near the workpiece in question, near the title block or in the space devoted to general notes.

    Indication with lettersReference indication in case of minimal drawing space = = z y z y =L Ra 0.9 U Rz 1.7 Ra 3.1
    Indication by graphical symbol alone

    The corresponding graphical may be used on the appropriate surface and its meaning given on the drawing as follows.

    Indication by graphical symbol aloneSimplified indication of surface texture requirements = = = Ra 3.1 Ra 3.1 Ra 3.1

    Left symbol for unspecified manufacturing process, middle symbol for removal of material required, Right symbol for removal of material not permitted.

    Indication of two or more manufacturing methods

    If it is necessary to define surface texture both before and after treatment, this shall be explained in a note or in accordance with Figure 29.

    Indication of two manufacturing methods Indication of surface texture requirement before and after treatmen 50 h7 Rz 1.5 Ra 0.9 Chromium plated

    Proportions and dimensions of graphical symbols


    In order to harmonize the size of the symbols specified in this International Standard with those of other inscriptions on technical drawings (dimensions, geometrical tolerances, etc.) the rules given in ISO 81714-1 are applicable.

    The height of all lettering in areas “a”, “b”, “d” and “e” in the following figure shall be equal to h.

    Positions (a to e)Positions (a to e) for location of complementary requirements d  b a c e
    The dimensions of the graphical symbols
    Height of numerals and letters2,53.557101420
    Line width for symbols, d'0.250.350.50.711042
    xLine width for lettering, d
    Height, H13.55710142028
    Height, H2 (minimum) a7.510.51521304260
    a   H2 depends on the number of lines of indication.

    Examples of indication of surface texture requirements

    All following examples are copied from ISO 1302:2002.

    Example 1

    Example 1Examples of indication of surface texture requirements C 0.008-4 / Ra 6.2 0.008-4 / Ra 55 milled

    Surface roughness:
    —   bilateral specification;
    —   upper specification limit Ra = 55 µm,
    —   lower specification limit Ra = 6,2 µm;
    —   both "16 %-rule”, default (ISO 4288);
    —   both transmission band 0,008-4 mm;
    —   default evaluation length (5 × 4 mm = 20 mm) (ISO 4288);
    —   surface lay approximately circular around the centre;
    —   manufacturing process, milling.
    NOTE   U and L is not stated because there is no doubt.


    Example 2

    Example 2Examples of indication of surface texture requirements Ra 0.7 Rz 6.1

    Surface roughness on all surfaces except one:
    —   one single, unilateral/upper specification limit
    —   Rz = 6,1 µm
    —   “16 %-rule”, default (ISO 4288);
    —   default transmission band (ISO 4288 and ISO 3274);
    —   default evaluation length (5 × λ c) (ISO 4288);
    —   surface lay, no requirement;
    —   manufacturing process shall remove material
    The surface with a different requirement has a surface roughness:

    —   one single, unilateral/upper specification limit;
    —   Ra = 0,7 µm;
    —   “16 %-rule”, default;
    —   default transmission band (ISO 4288 and ISO 3274)
    —   default evaluation length (5 × λ c) (ISO 4288);
    —   surface lay, no requirement;
    —   manufacturing process shall remove material.


    Example 3

    Example 3Examples of indication of surface texture requirements -2.5 / Rzmax 6.7 Ra 1.5 ground

    Surface roughness:
    —   two, unilateral/upper specification limits:
    1)   Ra = 1,5 µm;
    2)   “16 %-rule”, default (ISO 4288);
    3)   default transmission band (ISO 4288 and ISO 3274);
    4)   default evaluation length (5 × λ c) (ISO 4288);
    5)   Rz max = 6,7 µm;
    6)   max- rule;
    7)   transmission band - 2,5 mm (ISO 3274);
    8)   evaluation length default (5 × 2,5 mm);
    —   surface lay approximately perpendicular on the projection plane;
    —   manufacturing process, grinding.


    Example 4

    Example 3Examples of indication of surface texture requirements Rz 1 Fe/Ni20P Cr r

    Surface roughness:
    —   a single unilateral/upper specification limit;
    —   Rz = 1 µm;
    —   “16 %-rule”, default (ISO 4288);
    —   default transmission band (ISO 4288 and ISO 3274);
    —   default evaluation length (5 × λ c) (ISO 4288);
    —   surface lay, no requirement;
    —   surface treatment: nickel/chromium coating;
    —   the surface requirement is valid for all surfaces represented by the closed outline.


    Example 5

    Example 3Examples of indication of surface texture requirements -0.8 / Ra 3.1 U -2.5 / Rz 18 L -2.5 / Rz 6.5 Fe / Ni10b Cr r

    Surface roughness:
    —   one unilateral upper specification:
    1)   unilateral Ra = 3,1 µm;
    2)   “16 %-rule”, default (ISO 4288)
    3)   transmission band - 0,8 mm ( λ s according to ISO 3274);
    4)   evaluation length 5 × 0,8 = 4 mm (ISO 4288);
    —   and one bilateral specification:
    1)   bilateral Rz;
    2)   upper specification limit Rz = 18 µm
    3)   lower specification limit Rz = 6,5 µm;
    4)   both: transmission band - 2,5 mm ( λ s according to ISO 3274);
    5) both: evaluation length 5 × 2,5 = 12,5 mm;
    (the symbols U and L may be indicated even if there is no doubt)
    —   surface treatment: nickel/chromium coating.


    Example 6

    Indication of surface texture and dimensioning may be combined using the same dimension line.

    Example 3Examples of indication of surface texture requirements 2 x 45 A A Ra 2.5 Ra 6.5

    Surface roughness on side surfaces of keyway:
    —   a single, unilateral upper specification limit;
    —   Ra = 6,5 µm;
    —   “16 %-rule”, default (ISO 4288);
    —   default evaluation length (5 × λ c) (ISO 3274);
    —   default transmission band (ISO 4288 and ISO 3274);
    —   surface lay, no requirement;
    —   manufacturing process shall remove material;
    Surface roughness on the chamfer:
    —   one single, unilateral/upper specification limit;
    —   Ra = 2,5 µm;
    —   “16 %-rule”, default (ISO 4288);
    —   default evaluation length (5 × λ c) (ISO 3274);
    —   default transmission band (ISO 4288 and ISO 3274);
    —   surface lay, no requirement;
    —   manufacturing process shall remove material.


    Example 7

    Example 3Examples of indication of surface texture requirements 40 R3 Rz 50 Ra 6.2 Ra 1.5

    Surface texture and dimensioning may be indicated
    —   together on an extended dimension line, or
    —   separated on the respective projection line and dimension line.
    The three surface roughness requirements on the example are all:
    —   one single, unilateral/upper specification limit;
    —   respectively: Ra = 1,5 µm, Ra = 6,2 µm, Rz = 50 µm;
    —   “16 %-rule”, default (ISO 4288);
    —   default evaluation length (5 × λ c) (ISO 3274);
    —   default transmission band (ISO 4288 and ISO 3274);
    —   surface lay, no requirement;
    —   manufacturing process shall remove material.

    Removal of material requiredExpanded graphical symbol indicating removal of material required

    Example 8

    Indication of surface texture, dimensioning and treatment. The example is illustrating three successive manufacturing processes or stages.

    Indication with lettersReference indication in case of minimal drawing space 25 h6 40 Rz 1.7 Rz 6.5 ground Fe/Cr50

    Stage 1:
    —   one single, unilateral/upper specification limit
    —   Rz = 1,7 µm
    —   “16 %-rule”, default (ISO 4288)
    —   default evaluation length (5 × λ c) (ISO 3274)
    —   default transmission band (ISO 4288 and ISO 3274)
    —   surface lay, no requirement
    —   manufacturing process shall remove material
    Stage 2:
    No surface texture requirement, except:
    —   chromium coating
    Stage 3:
    —   a single, unilateral/upper specification limit, only valid for the first 50 mm of the cylinder surface;
    —   Rz = 6,5 µm
    —   “16 %-rule”, default (ISO 4288)
    —   default evaluation length (5 × λ c) (ISO 3274)
    —   default transmission band (ISO 4288 and ISO 3274)
    —   surface lay, no requirement
    —   manufacturing process grinding


    • References:
      • Geometrical Dimensioning and Tolerancing for Design, Manufacturing and Inspection, Georg Henzold
      • Surface roughness, From Wikipedia
      • ISO 1302
      • Jenoptic Leaflet
      • Manual of engineering drawing, Colin H Simmons 2004