Image, designation of typical parts and dimensioning on their drawings
When designing many parts, common elements such as chamfers, grooves, grooves, grooves for screw heads, etc. are widely used. Some of these elements, characteristic of threaded parts, such as chamfers, grooves for the exit of a thread-cutting tool ( see Figure 14.20), hex head "turnkey" bolts and nuts are discussed above (see § 13.2).
Let's consider in addition images of such structural elements of details, as chamfers, corrugations, scales and inscriptions, grooves under sealing rings from felt or felt, and also such those
Nologic elements, such as center holes and grooves for the exit of the grinding wheel. At the same time, the dimensional patterns and standard designations typical for these elements will be considered.
Chamfers protect the sharp edges of the parts from the nicks, which is important to ensure the assembly of parts. Chamfers on external structural elements are often important for ease of use. Widely used bevels at an angle of 45 ° to the surface are usually denoted with x & apos; 45 °, where c is the size of the bevel of the chamfer. If the chamfer is located at a different angle a, then its dimensions are applied, as shown in Fig. 14.43, or specify the angle and one linear dimension (a), or two linear dimensions (b).
Corrugations on the surface of a part are widely used to eliminate slippage of the part in the hand when turning. Examples of straight and mesh corrugations on the head of the part are shown in Fig. 14.44. For simplified images in the drawings, see Fig. 13.35 and 14.46. A simplified image of the type of corrugation is accompanied by an inscription indicating the step of corrugations. Thus, in the drawing in Fig. 14.46 pitch of corrugations is indicated 1 mm. The dimension D (see Figure 14.46) denotes the diameter of the cylindrical surface of the workpiece, on which the corrugation is formed. This size increases somewhat after corrugation.
Inscriptions, marks, scales , applied on a flat surface, are depicted in the corresponding form completely, regardless of the way they are applied. Their arrangement and outline should meet the requirements for the finished product.
If the inscriptions and signs are applied to a cylindrical or conical surface, then the image of this surface in the form of a sweep is placed in the figure (Figures 14.45, 14.46) with the required arrangement of signs and digits on the sweep.
The technical requirements in the drawing indicate the required data for
elements of scales, numbers, font, background, cover, etc. (see Figure 14.45, 14.46).
O-ring grooves (Figure 14.47). The shape of the grooves is selected from the conditions for ensuring that a felt or felt seal ring is clamped with a rectangular section to the smooth cylindrical surface of the sealing part. The above design of the groove ensures the compression of the shaft with a sealing ring. To specify the dimension b and the angle a (usually 15 °), a detail element is used with the image magnification, and the diameters D, D1 and the size a of the axial position grooves are applied to the main image.
Technological center nests. Non-hollow parts such as bodies of rotation - shafts are usually machined on lathes or grinders and controlled in centers that enter the conical center nests at the ends of the part (Figure 14.48). Their shape and dimensions are taken in accordance with GOST 14034-74, depending on the diameter of that part of the part in which the socket is made. An example of a drawing with a center socket and its designation in the drawing is shown in Fig. 14.49, a.
Center sockets may be necessary in the case of operation in case of repair by additional processing, for example, grinding. In this case, the center nests point to the drawing of the part, and their outer edge is made with a protective facet (see Figure 10.11, d). Chamfer p, in this case, protects the working conical surface p from damage. If the center nests on the finished part are inadmissible, a sign is placed on the drawing (Figure 14.49, b).
In those cases where the presence of center nests is constructively indifferent, they are not represented in the drawing and no specifications are placed in the technical specifications.
Technological grooves for the exit of the grinding wheel. When grinding, the edges of the grinding wheel are always slightly rounded (this rounding in figure 14.50 is indicated by the radius R). In this regard, for machining a cylindrical or flat surface, the part is provided with a technological groove for the exit of the rounded edges of the grinding wheel. The shape and dimensions of the grooves for the exit of the grinding wheel are standardized in GOST 8820-69 and are shown in Fig. 14.51 for external (a) and internal (b) grinding on the cylinder. If the form of the groove and dimensioning is difficult to perform in the part drawing, then it is represented by an outward element - a local view or a cut.
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