Specifying the Manufacturing Method by Surface Roughness

The manufacturing method, machining, coating, or other rules relating to the manufacturing process are written in the area of the symbol marked “b.” When the desired surface condition must be obtained by a specific manufacturing method, that method is indicated with a word ending in “-ed” (turned, milled, chrome-plated, etc.) written above the horizontal line added to the symbol’s long leg.

manufacturing method in surface roughness

Indicating the surface conditions before and after machining together. Figure a, above.

If there isn’t enough room to write the text, an extra line can be drawn above the horizontal line. Figure b, above.

Sampling Length and Waviness

Alongside the relevant symbol, the waviness value (Wt) and the sampling length value used for inspection (L) are written in the area of the symbol marked “c.” Sampling length values are chosen from one of the series 0.08 – 0.80 – 8 – 0.25 – 2.5, and 25 mm, per TS 6212.

The Ra Value

Surface roughness is most commonly expressed in microns using the Ra (average roughness) value.

Effect of Machining Method

Grinding generally achieves much lower (smoother) Ra values than turning.

Functional Importance

Surface roughness directly affects a part’s friction, wear, and sealing performance.

Lay (Surface Texture)

When the texture of the machined surface — and in particular the direction of the tool marks — needs to be specified, the relevant symbol should be written in field “d” of the surface condition symbol.

The standard symbols used to indicate the shape and direction of the tool marks (parallel, perpendicular, crossed, etc.) are shown.

lay directions in surface finish symbols

Machining Allowance

When it’s necessary to indicate the extra machining allowance on parts obtained by processes like casting or forging, this value is written in millimeters in the area of the symbol marked “e,” as shown below.

Other roughness values besides Ra are written, along with their symbol, in μm in the area of the symbol marked “f.” Values such as Rg, Rz, and Rp can also be written in area “a,” as indicated in the relevant standard, in addition to area “f.”

Examples for Better Understanding Surface Finish Symbols

Related Questions

Some surface properties can only be achieved with a specific manufacturing method. These notes clearly tell the manufacturer which method should be used to machine that surface, guaranteeing the desired quality is achieved.

Grinding removes very small amounts of material from the surface using a large number of tiny abrasive grains. This fine, precise machining produces a much smoother surface than the more pronounced cutting marks left by turning.