Under normal conditions with high speed steel tools and comparatively low cutting speeds the continuous chips from a piece of cutting metal are seldom dangerous provided they are controlled and directed by suitable front and side rakes.
When turning operation is being carried out at very high speed, then the hot sharp-edged cuttings are liable to become dangerous and it may be necessary to reduce the length of the spiral and cause the chips to break off into short lengths. Any interference with the free action of the chips is detrimental to the free cutting action of the tool; further the chips also spoil the finish of the machined surface.
Chip breakers for the cutting of metals are in the form of a set or groove ground on the rake faces in the case of brazed carbide tools, and pre-sintered chip breakers in the case of disposable inserts.
A simple and effective method of breaking the chips is to grind a small curved lip on the cutting edge of the tool; or to provide an independent chip breaker secured to, or laid on the top of the tool, and held in position by the tool holder dogs.
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Generally a square piece or steel of the same length as the tool with one end ground slightly concave or convex is found to be quite effective in breaking the chips, and it can be readily adjusted to the best advantages. This type of arrangement is best suited for mechanically clamped disposable insert type tools.
The carbide piece (chip breaker) is mechanical held over tool insert. Effective chip breaking depends on the distance of the chip breaker from the cutting edge.
Another method is to grind a narrow groove longitudinal with the cutting edge as shown in Fig. 12.101. The groove is not carried to the edge of the tool and the width of metal, or land, between the groove and the cutting edge will depend upon the amount of feed and the hardness of metal being cut. The greater the feed and the harder the metal, the wider the land.
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