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Has anyone ever encountered a situation where, when drawing to a certain part of the diagram, they suddenly don’t know how to proceed? Don’t worry; the following classic standards for mechanical drawing explain the methods for drawing components such as shaft sleeves, discs and covers, fork frames, and box types, as well as providing information on surface roughness and tolerance fits. Part 1: Knowledge of Mechanical Drawing and Dimensioning 1. Shaft and sleeve-type parts. Such parts generally include shafts, bushings, etc. When representing them in drawings, it is sufficient to draw one basic view along with appropriate sectional views and dimensioning in order to show their main geometric features as well as their local structures. To facilitate viewing of the drawings during processing, the axis is generally projected in a horizontal position; it is best to choose a location where the axis is a vertical line. http://www.cmiw.cn/data/attachment/forum/201903/05/105256ow2vt29l2b9h2n3t.jpg When specifying the dimensions of shaft sleeve-type parts, their axis is often used as the reference for radial dimensions. From this, Ф14, Ф11 (see cross-section A-A), etc. shown in the figure are indicated. This unifies the design requirements with the manufacturing process criteria (when machining shaft components on a lathe, the center hole of the shaft is supported at both ends by thimbles). The reference for the length direction is typically chosen from important end faces, contact surfaces (shaft shoulders), or machined surfaces. As shown in the image, the right shoulder with a surface roughness of Ra6.3 is selected as the main dimension reference in the length direction; dimensions such as 13, 28, 1.5, and 26.5 are indicated based on this ； Using the right end of the shaft as an auxiliary base in the length direction, the total length of the shaft, 96, is then indicated. 2. Disk and cover-type parts: These parts have a basically flat disc-shaped form. Examples include end caps, valve covers, gears, etc. Their main structural element is a rotatable body, which usually also features various shapes of flanges, evenly distributed circular holes, and ribs as additional structural elements. When selecting views, it is common to choose a sectional view taken along the symmetry plane or axis of rotation as the front view; at the same time, appropriate additional views (such as the left view, right view, or top view) are needed to show the shape and the uniform layout of the part. As shown in the figure, a left view has been added to illustrate the rounded square flange and the four evenly distributed through-holes. http://www.cmiw.cn/data/attachment/forum/201903/05/105257vpp0cxsqps9cce8v.jpg When marking the dimensions of disc-shaped parts, the axis passing through the shaft hole is usually chosen as the reference for radial dimensions, while the main reference for length dimensions is typically an important end face. 3. Fork-type components: These components generally include shift forks, connecting rods, supports, and other similar parts. Due to their variable processing positions, when selecting the front view, the working position and shape characteristics are primarily considered. For the selection of other views, two or more basic views are often required, and appropriate methods such as local views and sectional views are also needed to represent the partial structure of the part. The view selection in the footrest part diagram is concise and clear. The right-side view is unnecessary for indicating the width of the bearings and ribs, while a cross-section is more suitable for T-shaped ribs. http://www.cmiw.cn/data/attachment/forum/201903/05/105258u09ut339i5rezxc5.jpg When marking the dimensions of fork-type components, the mounting surface or the symmetrical plane of the component is usually used as the dimensioning reference. Refer to the figure for the dimensioning method. 4. Box-type parts: Generally speaking, the shape and structure of these parts are more complex than those of the previous three types, and there are more variations in their machining locations. Such components generally include parts such as the valve body, pump body, and reducer housing. When selecting the front view, the working position and shape characteristics are primarily considered. When selecting other views, appropriate auxiliary views such as sectional views, cross-sectional views, local views, and inclined views should be used according to the actual situation, in order to clearly illustrate the internal and external structure of the part. http://www.cmiw.cn/data/attachment/forum/201903/05/105259y3mapnmwxa3wqrza.jpg When indicating dimensions, it is common to use the axes specified in the design, important installation surfaces, contact surfaces (or machining surfaces), as well as the symmetry planes of certain key structural elements of the enclosure (width, length), etc., as benchmarks for dimensions. For the parts on the box that require machining, the dimensions should be marked as much as possible in a way that facilitates machining and inspection. 5. Dimensions of common part structures; Methods for indicating the dimensions of common holes (blind holes, threaded holes, counterbored holes, reamed holes) ； Notation for the dimensions of chamfers. http://www.cmiw.cn/data/attachment/forum/201903/05/105301fhc2g0z02525368d.jpg Blind hole http://www.cmiw.cn/data/attachment/forum/201903/05/105303tunh5cmymn2req6c.jpg Threaded hole http://www.cmiw.cn/data/attachment/forum/201903/05/105306r1mkj193v0ymt4v1.jpg Countersunk hole http://www.cmiw.cn/data/attachment/forum/201903/05/105308y485szc5be5e5o55.jpg Flattened hole http://www.cmiw.cn/data/attachment/forum/201903/05/105310egnf3axzrxe3aafs.jpg Chamfering. Due to limitations, the content is incomplete; for more details, please search using the title