Compensation On Path - Siemens SINUMERIK 840D sl Function Manual

W5: 3D tool radius compensation
19.3 Face milling
In addition to the usual methods of programming orientation, it is also possible to refer the tool
orientation to the surface normal vector and path tangent vector using the addresses LEAD
(lead or camber angle) and TILT (side angle). The lead angle is the angle between the tool
orientation and the surface normal vector. The side angle is the angle between the path
tangent and the projection of the tool vector into the surface to be machined. Specification of
the angle relative to the surface normal is merely an additional option for programming tool
orientation at the block end. It does not imply that the lead and side angles reach their
programmed values before the path end point is reached.
The final tool orientation is calculated from the path tangent, surface normal vector, lead
angle and side angle at the block end. This orientation is always implemented by the end of
the block, particularly in cases where the block is shortened (at an inside corner). If the
omitted path section is not a straight line in a plane, the lead and side angles generally
deviate from their programmed values at the path end point. This is because the orientation
has changed relative to the surface normal vector or path tangent vector when the absolute
orientation of the tool is the same as at the original path end point.
19.3.3

Compensation on path

Tool longitudinal axis parallel to surface normal
A special case must be examined with respect to face milling operations, i.e. that the
machining point on the tool surface moves around. This may be the case on a torus cutter
whenever surface normal vector n
right angles to the surface) since it is not a single point on the tool that corresponds to this
direction, but the entire circular surface on the tool end face. The contact point is not,
therefore, defined with this type of orientation. A path point in which tool longitudinal axis and
surface normal are parallel is therefore referred to below as a singular point or a singularity.
The above case is also meaningful in practical terms, e.g. in cases where a convex surface,
which may have a vertical surface normal (e.g. hemisphere), must be machined with a
perpendicular tool (e.g. face milling with constant orientation). The machining point on the
contour remains fixed, but the machine must be moved to bring the machining point from one
side of the tool to the other.
The problem described is only a borderline case (lead angle β = 0 and side angle y = 0). If the
lead angle β = 0 and the side angle y has a low value, then the tool must be moved very
rapidly (in borderline case in steps) to keep the machining point resulting from the milling
conditions close to the arc-line forming the end face, see the following Figure.
712
and tool vector w become collinear (i.e. the tool is at exact
F
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
Special Functions