Denotation of Roughness of Surfaces

The roughness of surfaces of the parts is marked on sketches and detail drawing s by conventional signs.

The roughness of surface is the aggregate of inequalities in the form of profile peak and profile valley which remain on the surface of the part as a result of the influence of a cutting instrument. For setting norms and evaluation of roughness of surface State Standard 2789-73 set six parameters among which the parameters of Ra are mainly used in practice (arithmetical mean deviation of the profile) and Rz – ten-point height of irregularities.

The roughness of surfaces on the drawings is shown according to State Standard 2.309-73 one of three signs: the sign, shown in figure 6.3 is used, when a designer does not set the type of treatment of surface; the sign, shown in figure 6.3 b is used for surfaces, got by a deplating material, for example, turning, drilling, milling; the sign, shown in figure 6.3 c is used for surfaces, got without a deplating material, for example, casting, die forging, rolling etc.

Figure 6.3 – The signs for roughness of surfaces

The height of h signs (fig.6.3) must be approximately equal the height of numbers of size numbers, and height H=(1,5-3)h . The thickness of lines of these signs equals the half of thickness of continuous mainline.

Denotations of roughness of surfaces are marked on a contour lines, extension lines, or on the shelves of line-foot-notes; when there is no space, it is allowed to write them on dimension lines.

If all surfaces, indicated on the drawing, have an identical roughness, its denotations are marked in the upper-right-hand corner of drawing, and no signs are put on the depiction. Sizes of this sign must be approximately 1,5 times more than on a drawing (fig.6.4, a).

Figure 6.4 – Sizes of this roughness sign

If the roughness of surfaces on the drawing is not identical, in upper-right-hand corner, after general denotation of identical roughness (for most surfaces), the sign of less size is put in brackets (fig.6.4, b). It means that all surfaces which have no signs of roughness on the depictions must have roughness, indicated in the upper-right-hand corner.