Module 1 : Introduction and geometric constructions

Lecture 1 : Introduction to Engineering Drawing

 

  1. French curve/Flexible curve

    2. French curve is free form template make of acrylic and is used to draw a smooth curve passing through a  number of points. The outer profile of the French curve is adjusted such the smooth curve passes through more than three points and a curve passing through these lines are drawn. The next part of the curve is then drawn by using the next three points in addition to the last two points of the previous curve.A typical French curve is shown in figure 6.
    A flexible curve is consists of a flexible, generally made of metallic wire coated with a thick rubber material. This can be bend in to any shape so that its working edge can be matched with a number of points and a smooth curve can be .

Figure 6. A typical French Curve.

Layout of drawing sheets


Any engineering drawing has to follow a standard format. The drawing sheet consist of drawing space, title block and sufficient margins. After fixing the drawing sheet on the drawing board, margins should be drawn.   The layout should facilitate quick reading of important particulars. Drawings are prepared at various locations and shared and quick references should be located easily.
A typical drawing sheet is shown in figure 4 and consist of the following:

  1. Borders – space left all around in between the trimmed edges of the sheet. A minimum of 10 mm
  2. Filling margin – 20 mm minimum on left hand side with border included. This is provided for taking perforations. 
  3. Grid reference system – For all sizes of drawing sheets for easy location of drawing within the frame. The length and the width of the frames are divided into even number of divisions. Number of divisions for a particular sheet depends on complexity of the drawing. The length of the grids  lies between 25 mm to 75mm depending on the Drawing sheet size. The grids along vertical edges are named by capital letters where as grids along the horizontal edges are by numerals. Numbering and lettering start from the corner of the sheet opposite to the title box and are repeated on the opposite sides. The numbers and letters are written upright. Repetition of letters or numbers like AA, BB, etc. are practiced in case they exceed that of the alphabets.