Machinery's Handbook, 31st Edition
838 Cutting Tools tool life was found to be 125 fpm (0.635 m/s) when the nose radius was 1 ⁄ and 160 fpm (0.8.13 m/s) when the nose radius was 1 ⁄ 4 inch (6.35 mm). A very large nose radius can often be used but a limit is sometimes imposed because the tendency for chatter to occur is increased as the nose radius is made larger. A nose radius that is too large can cause chatter, and, when it does, a smaller nose radius must be used on the tool. It is always good practice to make the nose radius as large as is compatible with the operation being performed. Chipbreakers.— Many steel turning tools are equipped with chipbreaking devices to pre vent the formation of long continuous chips in connection with the turning of steel at the high speeds made possible by high-speed steel and especially cemented carbide tools. Long steel chips are dangerous to the operator and cumbersome to handle, and they may twist around the tool and cause damage. Broken chips not only occupy less space, but per mit a better flow of coolant to the cutting edge. Several different forms of chipbreakers are illustrated in Fig. 4. Angular Shoulder Type: The angular shoulder type shown at A is one of the commonly used forms. As the enlarged sectional view shows, the chipbreaking shoulder is located back of the cutting edge. The angle a between the shoulder and cutting edge may vary from 6 to 15 degrees or more, 8 degrees being a fair average. The ideal angle, width W and depth G , depend upon the speed and feed, the depth of cut, and the material. As a general rule, width W , at the end of the tool, varies from 3 ⁄ 32 to 7 ⁄ 32 inch (2.4–5.6 mm), and the depth G may range from 1 ⁄ 64 to 1 ⁄ 16 inch (0.4–1.6 mm). The shoulder radius equals depth G . If the tool has a large nose radius, the corner of the shoulder at the nose end may be beveled off, as illustrated at B , to prevent it from coming into contact with the work. The width K for type B should equal approximately 1.5 times the nose radius. Parallel Shoulder Type: Diagram C shows a design with a chipbreaking shoulder that is parallel with the cutting edge. With this form, the chips are likely to come off in short curled sections. The parallel form may also be applied to straight tools that do not have a side cutting-edge angle. The tendency with this parallel shoulder form is to force the chips against the work and damage it. K 16 inch (1.59 mm)
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Fig. 4. Different Forms of Chipbreakers for Turning Tools Groove Type: This type (diagram D) has a groove in the face of the tool produced by grinding. Between the groove and the cutting edge, there is a land L . Under ideal condi tions, this width L , the groove width W , and the groove depth G , would be varied to suit the feed, depth of cut and material. For average use, L and G are about 1 ⁄ 32 inch (0.79 mm), and W 1 ⁄ 16 inch (1.59 mm). There are differences of opinion concerning the relative merits of the groove type and the shoulder type. Both types have proved satisfactory when properly proportioned for a given class of work.
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