机械制图制图的基本知识和技能（2）

　　今天我们学习《机械制图》——制图的基本知识和技能第二部分的内容。主要包括三部分内容，分别是绘制机械图样的三种方法，仪器绘图的仪器，工具及其用法，仪器绘图的制图步骤。Today we are studying the second part of Mechanical Drawing - Basic Knowledge and Skills of Drawing. The three main parts of the course are the three methods of drawing mechanical drawings, instruments for instrument drawing, tools and their usage, and the drafting steps for instrument drawing.
　　No. 1 绘制机械图样的三种方法
　　绘制机械图样有仪器绘图，徒手绘图，计算机绘图三种方法。
　　仪器绘图又称尺规绘图，主要依靠绘图仪器和制图工具作图，而最主要的仪器是圆规和分规，最主要的制图工具是丁字尺，三角板和直尺。
　　There are three methods of drawing mechanical drawings: instrument drawing, freehand drawing and computer drawing.
　　Instrument drawing, also known as ruler drawing, relies mainly on drawing instruments and drafting tools to make drawings, while the most important instruments are circular and minute gauges, and the most important drafting tools are the thumbscrew, triangle and straightedge.
　　No. 2仪器绘图的仪器，工具及其用法
　　常用的绘图仪器有圆规，分规等，常用的工具有图板，丁字尺，三角板，比例尺，曲线板，绘图铅笔等，其他的还有胶带纸，削笔刀，砂纸，橡皮等。
　　（一）铅笔以及用铅笔沿尺边画线的方法
　　（二）圆规和分规
　　圆规：用于画圆和圆弧
　　分规：常用于以试分法等分线段和圆周或圆弧
　　（三）曲线板的用法
　　曲线板用于画非圆曲线。已知曲线上的离散点愈密，曲线的准确度愈高。
　　Commonly used drawing instruments are circular gauges, minute gauges, etc. Commonly used tools are drawing boards, dashboards, triangles, scale bars, curve boards, drawing pencils, etc. Others are tape paper, pencil sharpeners, sandpaper, erasers, etc.
　　(i) Pencil and the method of drawing lines along the edge of the ruler with a pencil
　　(ii) Circle and parting gauges
　　Round gauge: used for drawing circles and arcs
　　Dividing gauge: often used to try to pide line segments and circumference or arcs by equal parts
　　(iii) Use of the curve board
　　Curve plates are used to draw non-circular curves. The more dense the discrete points on a known curve, the more accurate the curve will be.
　　No. 3仪器绘图的制图步骤
　　1.制图前的准备工作
　　（1）准备工具
　　准备好所用的绘图工具和仪器，磨削好铅笔及圆规上的铅芯
　　（2）安排工作地点
　　使光线从图板的左前方射入，并将需要的工具放在方便之处，以便顺利的进行制图工作
　　（3）固定图纸
　　一般是按对角线方向用胶带纸顺次固定，使图纸平整。
　　2.画底稿的方法和顺序
　　画底稿时，宜用削尖的H或2H铅笔轻淡地画出，并经常磨削铅笔。
　　一般步骤为：先画图框，标题栏，后画图形。画图形时，先画轴线或对称中心线，再画主要轮廓，然后画细部；如图形是剖视图或断面图时，则最后画剖面符号或剖面线，剖面符号或剖面线在底稿中只需画出一部分，其余可待加深时再全部画出。
　　1. Preparatory work before drawing
　　(1) Preparation of tools
　　Prepare the drawing tools and instruments to be used, sharpen the pencils and the lead cores on the roundels
　　(2) Arranging the working place
　　The light is directed from the left front of the drawing board and the necessary tools are placed in a convenient place so that the drawing can be carried out smoothly.
　　(3) Fixing the drawing
　　The drawing is usually fixed in a diagonal direction with tape paper in order to make it flat.
　　2. Method and order of drawing the base
　　When drawing the base drawing, it is advisable to use a sharpened H or 2H pencil to draw lightly and to sharpen the pencil frequently.
　　The general procedure is: draw the drawing frame first, the title bar, and then the figure. When drawing a figure, draw the axis or centre line of symmetry first, then the main outline, then the details; if the figure is a sectional view or section, draw the section symbol or section line last, the section symbol or section line should only be drawn partly in the base, the rest can be drawn when deepening.
　　文字|灯 等
　　排版|灯 等
　　审核|程丽燕
　　参考资料：文字：百度；图片：微博；翻译：百度翻译
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