The only tools needed would be the steel scale and something to make a mark with. The steel scale, or rule, used as a layout tool, has already been discussed.
If you were asked to divide the steel rod into parts, to lay off a given distance from some point marked on it, or to repeat a given dimension upon it a number of times, you would use some form of dividers. The dividers, as we have seen, consists of two legs fastened together at one end and pointed at the other. Various forms of dividers, adapted to different purposes, have been discussed on pages 12-15. Similar to dividers are the trammel, used to scribe circles too large to be scribed with a divider, and the compass, which is similar to the divider except that one leg holds a pencil.
As we have seen, the dividers, the trammel, and the marking gage are all used to scratch or scribe lines on metal or wooden surfaces. A special instrument called a scriber may be used to mark lines on wood or metal when the location of the line has been determined by layout tools. The scriber is a long narrow pencil-like tool. It consists of a long, hard, pointed end on a handle, which is usually knurled to provide a good grip for the hand. Scribers come in many sizes and in different shapes. Sometimes the scriber has a point on each end, one of them bent at a right angle to the rest of the tool. Such scribers have the knurled handle grip in the middle. You may turn them around and use whichever end is more convenient.
Use of the square
Suppose we want to lay out a rectangular piece of sheet metal 2" long and 1" wide. Now width, as well as length, must be considered. Since the piece is rectangular, its width must be at right angles with its length. If one edge is straight, one arm of the square is lined up with it. Any line, therefore, scribed on the other leg of the square must be at right angles with this first straight edge. Thus, using the proper dimensions, a perfectly rectangular piece can be simply and quickly laid off with the square.
However, if no edge of the metal stock is straight, a steel scale or one leg of the square must be used for scribing a straight line near one of the edges. This straight line is then used as the straight edge for setting the square properly and scribing lines at right angles to it. This principle is basic in all layout work. Start with a line and lay off all other lines in fixed relation to this line.
Use of the center punch
If holes are to be drilled, a square is used to scribe lines corresponding to the center lines in the drawing. Where these lines intersect, a mark is made by plating the center-punch point on it and tapping the punch once with a hammer. This punch mark will be used later for guiding the drill point in making the hole.
Much of layout consists in locating points. As in the case of the drilled hole, these points are located by intersecting lines. Where they intersect, the center punch may be used to make a light mark. This mark is an aid to the eye when working to the line. It may serve to center the dividers in the process of laying out; should the lines locating the point become obscured or blurred it serves in replacing them.
In sheet-metal work mechanics sometimes lay out the project on a piece of heavy paper instead of directly marking off the metal. In practice this paper, called a pattern or stretch-out, is laid on the metal and all intersections are transferred by center punching through the paper. The layout is then completed by connecting the punch marks with scribed lines.
Helps in laying out
In order to make lines and points easily visible, a surface may be rubbed with chalk. Then scribed lines appear dark on a white background.
Machinists and toolmakers of ten copperplate steel and iron surfaces in preparation for scribing. This is done by thoroughly cleaning the surf ace and polishing it with emery cloth. A solution of copper sulfate and water is made and kept in a glass or porcelain container. The surf ace of the steel or iron plate is covered with a thin layer of this solution. Chemical action soon causes a thin layer of copper to be deposited on the steel or iron plate. Washing with clear water removes the chemical and prevents further action. Then fine, accurate markings can be made on the surface.