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5.2 THE MECHANISM OF CUTTING

•Assuming that the cutting action is continuous we can develop a continuous model of cutting conditions.

•Orthogonal Cutting - assumes that the cutting edge of the tool is set in a position that is perpendicular to the direction of relative work or tool motion. This allows us to deal with forces that act only in one plane.

chip

friction

tool

•We can obtain orthogonal cutting by turning a thin walled tube, and setting the lath bit cutting edge perpendicular to the tube axis.

•Next, we can begin to consider cutting forces, chip thicknesses, etc.

•First, consider the physical geometry of cutting,

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t2

α

tool

t1

where,

t1 = undeformed chip thickness

t2 = deformed chip thickness (usually t2 > t1) α = tool rake angle

If we are using a lathe, t1 is the feed per revolution

• Next, we assume that we are also measuring two perpendicular cutting forces that are horizontal, and perpendicular to the figure above. This then allows us to examine specific forces involved with the cutting. The cutting forces in the figure below (Fc and Ft) are measured using a tool force dynamometer mounted on the lathe.