Machinery's Handbook, 31st Edition
THREAD GRINDING 2193 Wheels with Edges for Roughing and Finishing.— The “three-ribbed” type of wheel has a roughing edge or rib which removes about two-thirds of the metal. This is followed by an intermediate rib which leaves about 0.005 inch (127 μ m) for the third or finishing rib. The accuracy obtained with this triple-edge type compares with that of a single-edge wheel, which means that it may be used for the greatest accuracy obtainable in thread grinding. When the accuracy required makes it necessary, this wheel can be inclined to the helix angle of the thread, the same as is the single-edge wheel. The three-ribbed wheel is recommended not only for precision work but for grinding threads which are too long for the multi-ribbed wheel referred to later. It is also well adapted to tap grinding, because it is possible to dress a portion of the wheel adjacent to the finish rib for the purpose of grinding the outside diameter of the thread, as indicated in Fig. 1 . Furthermore, the wheel can be dressed for grinding or relieving both crests and flanks at the same time.
Fig. 1. Wheel with Edges for Roughing and Finishing
Fig. 2. Multi-Ribbed Type of Thread-Grinding Wheel
Fig. 3. Alternate-Ribbed Wheel for Grinding the Finer Pitches Multi-Ribbed Wheels.— This type of wheel is employed when rapid production is more important than extreme accuracy, which means that it is intended primarily for the grind ing of duplicate parts in manufacturing. A wheel 1 1 ∕ 4 to 2 inches (3.175–5.08 cm) wide has formed upon its face a series of annular thread-shaped ridges (see Fig. 2 ); hence, if the length of the thread is not greater than the wheel width, a thread may be ground in one work revolution plus about one-half revolution for feeding in and withdrawing the wheel. The principle of operation is the same as that of thread milling with a multiple type cutter. This type of wheel is not inclined to the lead angle. To obtain a Class 3 fit, the lead angle should not exceed 4 degrees.
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