20 Budynas-Nisbett:Shigley's I.Basics 1.Introduction to T©The McGraw-Hil Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design 14 Mechanical Engineering Desigr Figure 1-2 400- 380 Cost versus tolerance/ 360 machining process. 340 (From David G.Ullman,The 320 Mechanical Design Process, 300 3rd ed.,McGrawHill,New 280 Material:steel Yok,2003.) 260 240 220 180 160 140 120 100 0 0 20 ±0.030±0.015±0.010±0.005±0.003±0.001±0.0005±0.00025 Nominal tolerances(inches) ±0.75±0.50±0.50±0.125 .±0.063..±0.025.±0.012.±0006 Nominal tolerance(mm) Semi- Rough turn Finish finish turn Grind Hone tum Machining opcrations Figure 1-3 140 A breakeven point. 120 Breakeven point 100 Automatic screw 80 3 40 Hand screw machine 40 60 80 100 Production As an example,consider a situation in which a certain part can be manufactured at the rate of 25 parts per hour on an automatic screw machine or 10 parts per hour on a hand screw machine.Let us suppose,too,that the setup time for the automatic is 3 h and that the labor cost for either machine is $20 per hour,including overhead.Figure 1-3 is a graph of cost versus production by the two methods.The breakeven point for this example corresponds to 50 parts.If the desired production is greater than 50 parts,the automatic machine should be used.Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design 20 © The McGraw−Hill Companies, 2008 14 Mechanical Engineering Design As an example, consider a situation in which a certain part can be manufactured at the rate of 25 parts per hour on an automatic screw machine or 10 parts per hour on a hand screw machine. Let us suppose, too, that the setup time for the automatic is 3 h and that the labor cost for either machine is $20 per hour, including overhead. Figure 1–3 is a graph of cost versus production by the two methods. The breakeven point for this example corresponds to 50 parts. If the desired production is greater than 50 parts, the automatic machine should be used. Figure 1–2 Cost versus tolerance/ machining process. (From David G. Ullman, The Mechanical Design Process, 3rd ed., McGraw-Hill, New York, 2003.) Figure 1–3 A breakeven point. 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 Rough turn Semi￾finish turn Finish turn Grind Hone Machining operations Material: steel Costs, % Nominal tolerances (inches) Nominal tolerance (mm) 0.030 0.015 0.010 0.005 0.003 0.001 0.0005 0.00025 0.75 0.50 0.50 0.125 0.063 0.025 0.012 0.006 0 0 20 40 60 80 100 20 40 60 80 100 120 140 Breakeven point Automatic screw machine Hand screw machine Production Cost, $