Basic Layout UNIT 10 BASIC LAYOUT OPERATIONS Operations Structure 10.1 Introduction Objectives 10.2 Preparing Surface for Layout 10.3 To Layout Parallel Lines to an Edge 10.4 To Layout Lines at Right Angles 10.5 To Layout Horizontal Lines Using a Surface Gauge 10.6 Laying Out Centre Holes 10.7 To Check the Accuracy of the Centre Layout 10.7.1 Divider Method 10.7.2 Lathe Centre Method 10.8 Summary 10.9 Key Words 10.1 INTRODUCTION The preparation of the work surface and laying out straight lines are the primary operations performed in order to make a layout. Since the accuracy of the finished workpiece depends upon the accuracy of the layout, proper care should be taken during the process. Combination tools are used where the accuracy is not important. Square head is used to lay out horizontal and parallel straight lines. The bevel protractor is used for laying out angles while the centre head is used to layout the centre of round and square workpiece. Objectives After studying this unit, you should be able to • know how to prepare the work surface for layout, • layout straight lines using : ¾ the scriber and combination square ¾ the surface gauge and surface plate ¾ the vernier height gauge and surface plate • locate centre holes by : ¾ hermaphrodite calipers ¾ centre head ¾ surface gauge. 10.2 PREPARING SURFACE FOR LAYOUT Layout lines must be visually plain. Therefore, the surface of the work is coated with a layout material so that scribed lines are seen easily. The surface must be clean and free from dust, grease, surface scale, oil, etc., otherwise layout material will not stick to it. There are a number of ways of coating the surface for layout. 13 Layout Design for (a) Commercial layout dye or bluing is generally used to coat work surfaces. It Tool Engineering is not expensive and dries very fast. Layout dye is generally applied with brush. (b) Chalk may be used into rough surfaces of castings. (c) Copper sulphate solution is used for coating machined surface. SAQ 1 Discuss briefly the preparation of surface for layout. 10.3 TO LAYOUT PARALLEL LINES TO AN EDGE Combination Square Method (a) Hold the workpiece in a vise whenever possible to avoid its motion during operation. (b) Remove all burrs from the edge of the work with a file. (c) Extend the steel rule at the desired distance beyond the body of the square. Always make sure that only half the graduation line can be seen. (d) Hold the base of square tightly against a machined edge with rule flat on the work surface. (e) Hold the scriber at an angle to keep the point against the end of the rule and tilt top of the scriber in a direction where the line is to be scribed. (f) Draw a sharp line along the end of the rule. (g) Move the square a short distance and again scribe along the end of the rule. (h) Continue moving of the square and scribing until the line is complete. (i) Check the location of scribed line. SAQ 2 How do you lay parallel line to an edge? 10.4 TO LAYOUT LINES AT RIGHT ANGLES Lines at right angle are laid out by placing the body of square against a machined edge of the work that is at right angle to the first edge. The general steps are as follows : (a) Remove all burrs from the edge of the work with a file. (b) Slide the square along the work until the edge of the rule is at desired distance. (c) Hold the base of the square tightly against the machined edge with the blade of the rule remaining flat on the work surface. (d) Scribe the line by keeping the point of scriber against the edge of the rule. (e) Check the location of scribed line. 14 10.4.1 Surface Gauge Method Basic Layout Operations The work, the base of the surface gauge, the base of the square and the surface plate should be clean when the lines are scribed with surface gauge method. To Set Surface Gauge to a Dimension (a) Clean the top surface of the surface plate. (b) Set the combination square on the surface plate. (c) Loosen the combination square lock nut and make sure that the end of the rule is down against the surface plate. (d) Tighten the lock nut of combination square. (e) Set the surface gauge on the surface plate. (f) Loosen the scriber clamp nut and adjust the scriber so that it is approximately at the desired dimension. (g) Tighten the scriber clamp nut to lock the scriber in position. (h) Turn the surface gauge thumb screw until the scriber point is in the centre of the desired graduation on the rule. SAQ 3 Explain the methods of laying out lines at right angles. 10.5 TO LAYOUT HORIZONTAL LINES USING A SURFACE GAUGES (a) Set the surface gauge to the desired dimension. (b) Place the edge of the work from which the line is to be scribed on the surface plate. (c) Hold the surface gauge down on the surface plate. (d) Draw the surface gauge along the work in the direction of arrow to scribe the line. Push will cause the scriber point to dig into the work which will result in faulty layout. (e) Reset the surface gauge with the combination square rule for each dimension. (f) Layout all the lines which are parallel to the edge resting on surface plate. Vernier Height Gauge Method When close tolerance is required, i.e. up to 0.02 mm, a vernier height gauge method should be used. The general steps of the method can be described as : (a) Clean the surface plate and the base of the height gauge thoroughly. (b) Hold the gauge so that scriber point is approximately 45o to the surface being laid out. (c) Press down firmly on the surface or height gauge base. (d) Pull the gauge to maintain an accurate layout. Push will cause the scriber point to dig into the work which results in inaccurate layout lines. 15 Layout Design for (e) If the work is first fastened to the angle plate, all horizontal lines can be laid Tool Engineering out as outlined. Therefore, the angle plate can be set on its edge (90o to the base) and the vertical lines can be laid out. SAQ 4 Explain the various methods to lay horizontal lines. 10.6 LAYING OUT CENTRE HOLES When the workpiece is to be machined between the centers on a lathe, it is necessary to layout and drill the centre holes before turning the work on a lathe. It is generally more accurate and convenient to drill the lathe centre holes in small round stocks on a lathe. This eliminates the need of laying out the holes. To Locate the Centers of Round Stock By Using Hermaphrodite Calipers (a) Place the work in a vise and remove the burrs or sharp edges. (b) Apply layout dye to both ends. (c) Set the hermaphrodite caliper to the approximate radius of the work. (d) Hold the bent leg with thumb below the edge of the work and scribe the arc. (e) Move the bent leg a quarter of a turn and scribe an arc. Repeat the procedure until four arcs are obtained at each end of the work. (f) Mark the centre of the arc using center punch and test the accuracy of the center. (g) Repeat the step 3 to 6 on the other end of the workpiece. By Using Center Head (a) Place the work in a vise and remove the burrs or sharp edges. (b) Apply layout dye to both ends. (c) Hold the centre head firmly against the work with the rule remaining flat on the end of the work. (d) Hold the sharp scriber at an angle so that its point touches the edge of the rule. (e) Scribe a line along the edge of the rule. (f) Rotate the centre head by one quarter of turn and scribe the second line. (g) Mark the point where two lines cross each other. (h) Repeat step 3 to 8 on the other end of the work. (i) Test the accuracy of the centre layout. Using Surface Gauge (a) Place the work in a V-block placed on surface plate and remove the burrs or sharp edges with the help of file. (b) Apply layout dye to both the ends. 16 (c) Set the scriber point of the surface gauge to the approximate centre of Basic Layout the work. Operations (d) Scribe four lines across the end of the work by rotating it by 90o for each line. (e) Mark the intersection of four lines by centre punch. (f) Test the center for accuracy by the divider or lathe centre method. SAQ 5 (a) Explain laying out center hole? (b) Discuss various steps involved in laying out center hole using center head. 10.7 TO CHECK THE ACCURACY OF THE CENTER LAYOUT It is necessary to check the accuracy of a layout before drilling the hole or machining the work. Also, great care should be taken while laying out lathe center hole. The centre of the hole offsets from the original position if an error occurs during the laying out. Two dividers are used to check the accuracy of the center hole layout. The accuracy of center layout is also checked by rotating the workpiece between the lathe centers. 10.7.1 Divider Method (a) Place one leg of the divider in light center punch mark.