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6.3 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.
              а)                  b)                 c)                  d)                e)










                                         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.

                         6.4 MAKING THE DETAIL DRAWINGS OF PARTS FROM SKETCHES


                  Unlike sketches the detail drawings of parts are done in a scale with the exact observance of
            sizes with the help of drawings instruments.
                  To make the detail drawings it is necessary:
                          to analyze preliminary the sketch of a part, in accordance with State Standard 2.302-
                           68 choose the scale of a view and a drawing format ;
                          to draw a frame and title block on a format;


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