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Southwestern Industries, Inc.
TRAK
KMX Knee Mill, Bed Mill & ProtoTRAK
KMX CNC Retrofit Safety, Programming, Operating & Care Manual
Special attention must always be paid to tool offsets when machining with a ball end
mill. The reason for this is that the tool diameter changes in the bottom part (that
portion equal to the tool radius) of the tool.
The tool is always positioned at the beginning of a milling operation so that the correct
point on the ball end of the tool is tangent to the beginning point, and offset perpen-
dicular to the machined edge by the radius of the tool. Consider the example below of
milling a ramp in the XZ plane from point B to point C.
FIGURE 5.7.1
Ball end mill position with respect to program points. Tool starts so
end mill is tangent to BC. R from center of tool is perpendicular to BC
Note how the tool at the beginning point (point B) starts below (in the Z direction) point
B so that it can actually touch this point. If this were not true, a cusp would remain to
the left of point B.
Now consider a similar example milling from A to B to C in the XZ plane.
FIGURE 5.7.2
In order to respect the lines defined by the programmed
points, the ball end mill never touches point B. Tool starts centered over A
offset up by the tool radius R. It moves right until it is tangent to both AB and
BC. Then moves to point C as in the first example
Note the Tool at B does not drop below the AB line and, therefore, never touches point
B. As a result, a fillet is formed at point B equal to the tool radius.
This second example of continuous machining from one cut (AB) to another (BC) with
full cutter compensation between requires the two cuts to be made with events which
are connective (see Section 5.8 or 5.9 for a more complete discussion of this
requirement).
