LATHE OPERATIONS - OD1645 - LESSON 1/TASK 3
Cutting Square Threads.
Because of their design and strength, square
threads are used for vise screws, jackscrews, and other devices where
maximum transmission of power is needed. All surfaces of the square thread
form are square with each other, and the sides are perpendicular to the
center axis of the threaded part (figure 51). The depth, the width of the
crest, and the root are of equal dimensions. Because the contact areas are
relatively small and do not wedge together, friction between the matching
threads is reduced to a minimum. This fact explains why square threads are
used for power transmission.
FIGURE 51. DETERMINING THE HELIX ANGLE
FOR A SQUARE THREAD.
(1) Before the square-thread cutting tool can he ground, it is necessary
first to determine the helix angle of the thread. The sides of the tool for
cutting the square thread should conform with the helix angle of the thread.