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3.4 Thread classifications Threads are classified according to four factors: 1. Purpose We distinguish between fastening threads and motion-transmitting threads. Fastening thread E Fastening threads are generally single-threaded V-shaped threads with an included thread angle of 60° (55°) and a maximum lead angle of 5°. The frictional forces generated by fastening threads must be high enough to prevent the components from loosening by themselves. If a fastening thread fulfils this condition, it is self-locking. Motion-transmitting thread E Motion-transmitting threads are used to convert rotational motion into linear motion or vice versa. Motion-transmitting threads have different profiles depending on the load and can be multi-threaded. 9 4.1.3 Taps for different materials Tap for steel The cutting geometry depends on the materials to be cut. Tap for steel α E α – clearance angle (only on starting taper) β E β – wedge angle E γ – rake angle approx. 5˚–10˚ γ Chip space Tap for non-ferrous metals Tap for non-ferrous metals Taps for non-ferrous metals have larger rake angles (γ) and wider flutes. The clearance angle (α) can go back to 0. The chips that are created during thread cutting are collected and carried away in the chip spaces. γ β Chip space α = 0˚ Guide values for rake angles on taps Material Rake angle γ Brass, bronze, hard cast iron, tough steel 0°. . . . . . .5° Steel up to 700 N/mm2 strength, cast iron up to 200 HB 5° . . . . . 10° Long-chipping light metals 20˚ . . . . 30˚ 21 4.7 Exercises with solutions Angular functions in a right-angled triangle Angular functions are geometric relations se enu t o Hyp α Adjacent side Opposite side α = known angle Hypotenuse = side located opposite the right angle. Adjacent side = side located adjacent to the known angle. Opposite side = side located opposite the known angle. Angular functions in a right-angled triangle sin α = Opposite side Hypotenuse cos α = Opposite side Adjacent side Adjacent side Hypotenuse ctg α = Adjacent side 1 = Opposite side tan α cos α = Exercise 1 Enter the function values of the following angles. Angle Function value sin α α cos α tan α ctg α 10° 20° 30' 35.6° Exercise 2 Identify the angles α and enter the results in degrees and minutes. Function value Angle α sin α = 0.1564 cos α = 0.8732 tan α = 1.3500 ctg α = 0.3915 35