Surface texture symbols, where to place requirements, and how to write Ra and Rz. 7 terms. For each term: meaning, how to show it on a drawing, an example, common mistakes, and JIS vs. ASME differences.
Printed from Kezuriba (kezuriba.net/en/drafting/surface/)
√Surface texture symbolshyomen seijo no zushikigosurface texture symbol
A symbol that specifies surface roughness, whether material removal is required, lay direction, machining method, and so on, all together. The basic symbol is a V opened at 60° with legs of different lengths; surfaces that require material removal use the symbol with the triangle closed, and surfaces without material removal use the one with a circle.[1][2][3]
The basic surface texture symbol is two lines of different lengths opened at 60°. Close the triangle for surfaces that need material removal, and add a circle for surfaces without material removal. Write the requirements in positions a to e.
How to write it on the drawing
Use the 3 symbols appropriatelyUse the basic symbol for surfaces where removal is optional, the closed-triangle symbol for surfaces that need material removal, and the circle symbol for surfaces with no removal.[1][2][3]
Write requirements around the symbola: transmission band or sampling length, parameter and its value; b: second and later parameters; c: machining method; d: lay and its direction; e: machining allowance.[2][1][3]
Touch the symbol to the surfacePlace the symbol on the outline representing the surface, its extension line, or a leader (orientation rules and drawing examples are from an excerpt of JIS B 0031 and Misumi).[2]
Group them if most are the sameIf most of the part has the same requirement, write it once near the title block, and write only the different surfaces individually.[2][4]
ExampleKeyence's example for a ground surface: "Grinding" above the long line of the material-removal symbol, "0.008-0.8/Rz6 4.8" below it, machining allowance "3" to the left of the symbol, and lay symbol "⊥" at lower right.[1]
Common mistakes
Writing only the number without the parameter symbolWhy: the same number means something entirely different depending on whether it is Ra or Rz.Fix: write the parameter symbol and value, as in "Ra 3.2".[2][1]
JIS and ASMEIn the US, ASME Y14.36 defines surface texture symbols (differences in detail could not be confirmed in this research).[9]
Standard: JIS B 0031:2003 (identical to ISO 1302:2002; amended in 2022). ISO 1302 has been withdrawn and replaced by ISO 21920-1:2021.[5][6][7][8]
How to write surface texture requirementsyokyu jiko no kakikataindication of surface texture requirements
The order of the requirements written at position a of the symbol. Write, in order: upper/lower limit, filter type, transmission band (λs−λc), parameter symbol, evaluation length (number of sampling lengths, standard is 5), acceptance rule (16% rule or max), and limit value. Omit items that are standard.[1][2]
Write the requirements at position a in this order: upper/lower limit, filter, transmission band, parameter and evaluation length, acceptance rule, and limit value. Omit items that are standard.
How to write it on the drawing
Omit if standardLeave out items at standard conditions and write only the necessary ones.[1]
Upper and lower limitsU for the upper limit, L for the lower limit. When specifying both, write them on two lines.[1][2]
Max rule: write maxWhen no measured value may exceed the limit, add max after the parameter symbol.[1][2]
Example"U "X" 0.008-0.8/Rz 6 max 4.8": upper limit, filter X, transmission band 0.008–0.8 mm, maximum height Rz, evaluation length of 6 sampling lengths, max rule, limit 4.8 µm. Normally the standard items are omitted and it is written like "Rz 4.8".[1]
Standard: JIS B 0031:2003. Acceptance rules are in JIS B 0633:2003 (cited by Misumi).[5][2]
Arithmetic mean roughness Rasanjutsu heikin arasaarithmetical mean roughness / Ra
The average of the absolute values of the height from the mean line on the roughness profile over the sampling length (unit µm).[10][3]
Arithmetic mean roughness Ra: the average of the absolute values of the height from the mean line on the roughness profile over the sampling length (µm). Not sensitive to an occasional deep scratch.
How to write it on the drawing
Write at position a of the symbolWrite the value after the parameter symbol, as in "Ra 3.2".[2][4]
ExampleShimane University's gear part drawing: the whole part is Ra 6.3, some surfaces have Ra 3.2 and Ra 1.6 specified individually, and the top shows the combined note "Ra 6.3 (Ra 3.2, Ra 1.6)".[4]
Common mistakes
Assuming Ra alone guarantees the function of a surfaceWhy: Ra is an average, so it carries no information about the shape of the irregularities and does not distinguish peaks from valleys.Fix: where needed, also specify a height parameter such as Rz.[11]
Standard: defined in JIS B 0601:2013; indicated per JIS B 0031.[12][6]
Maximum height roughness Rz (formerly Ry) and RzJISsaidai takasa arasamaximum height of profile / Rz / RzJIS
Rz is the sum of the height of the highest peak and the depth of the deepest valley within the sampling length (maximum height roughness). In the 2001 JIS revision the old JIS maximum height Ry became Rz, and the old JIS ten-point mean roughness Rz was renamed RzJIS to distinguish them.[13][14][2]
Maximum height roughness Rz: the sum of the height Rp of the highest peak and the depth Rv of the deepest valley within the sampling length (µm). Corresponds to Ry in the old JIS.
How to write it on the drawing
At position a of the symbolWrite the parameter symbol and value, as in "Rz 6.3".[1][2]
Common mistakes
Reading "Rz" on an old drawing as today's RzWhy: Rz in JIS up to the 1994 edition was ten-point mean roughness, a different parameter from today's Rz (maximum height).Fix: check the drawing's date and the standard it follows, and treat the old Rz as RzJIS.[14][2]
Standard: JIS B 0601:2013 (Ry became Rz in the 2001 revision).[12][14]
=Lay direction symbolssujime hoko no kigolay symbols / direction of lay
Symbols that specify the direction of the tool marks (lay) left by material-removal machining. = is parallel to the plane of projection, ⊥ is perpendicular to it, X is crossed in two oblique directions, M is crossed in many directions, C is roughly concentric about the center of the surface, R is roughly radial, and P is particulate (pits or protrusions) or non-directional.[2][1]
Lay symbols: the direction of the tool marks is written at position d of the symbol. C for a turned end face, M for a face-milled or end-milled surface, P for an EDM or blasted surface, and so on.
How to write it on the drawing
Write at position dWrite the lay symbol at lower right of the surface texture symbol (position d).[2][1][3]
ExampleUse "⊥" to make the lay perpendicular to the plane of projection on shaped, turned, or ground surfaces; "M" for face-milled or end-milled surfaces; "C" for turned end faces; "R" for ground end faces; and "P" for EDM or blasted surfaces.[2][1]
Common mistakes
Not specifying a direction on a surface where lay affects functionWhy: the machinist chooses the direction for convenience of the process, so it may not be what was intended.Fix: specify the direction with a symbol only on surfaces where lay matters functionally.[11]
16% rule and max rulejuroku pasento ruru16% rule / max rule
How pass/fail is decided for surface texture. Under the 16% rule (the default), the surface passes if no more than 16% of the measured values exceed the upper limit. Under the max rule, specified by adding max to the parameter symbol, no measured value may exceed the upper limit.[2][3]
How to write it on the drawing
The default is the 16% ruleWithout max, the 16% rule applies.[2][3]
Max rule: write maxAdd max, as in "Rz max 4.8".[2][1]
ExampleProcedure for the 16% rule introduced by Mitutoyo America: if the first measurement is below 70% of the upper limit, it passes. Otherwise measure at 2 more locations; if all 3 are below the upper limit, it passes. If still undecided, measure at 9 more locations; if no more than 2 of the 12 total exceed the upper limit, it passes.[3]
Common mistakes
Failing the part right away if one measurement slightly exceeds the upper limitWhy: under the 16% rule, the procedure decides using additional measurements.Fix: if the drawing has no max, judge using the 16% rule procedure.[3][2]
Standard: JIS B 0633:2003 (cited by Misumi), ISO 4288.[2][3]
Simplified indication when most surfaces have the same surface texturekanryaku zushisimplified indication of surface texture
An abbreviation for when most of the part has the same surface texture: write that requirement once near the title block, followed in parentheses by the individually specified requirements (or just the basic symbol).[2][4]
If most surfaces have the same surface texture, write it together near the title block, as in "Ra 6.3 (Ra 3.2, Ra 1.6)". What is outside the parentheses applies to most surfaces; inside are the surfaces specified individually in the drawing.
How to write it on the drawing
Group them near the title blockWrite the requirement for most surfaces, followed in parentheses by the individually specified requirements (or just the basic symbol).[2][4]
Example"Ra 6.3 (Ra 3.2, Ra 1.6)": outside the parentheses is the requirement for most surfaces; inside are the requirements for surfaces specified individually in the drawing.[4][2]
Explanations without a mark are those on which two or more sources from different publishers agree. Because the text of the standards is paid, they were checked against technical materials from measuring-instrument and parts manufacturers, teaching materials from universities and public testing institutes, and public pages of the standards, and the explanations are written in Kezuriba's own words. The diagrams of the entry fields were drawn by Kezuriba.