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Fig 2.11 an example of a sliced CAD file
The main exercise of the slicing process would be to get the intersection points, as
all the curves are made up of small sections of lines and planar triangles put together
form the facets of the solid model. These intersection points are used in generating
the tool path cutter information later on. The rapid prototyping machine is not able to
point out which part is solid, because the resultant of the intersection just gives a set
of lines. Lin et all in 2002 mentions that the counter clockwise and clockwise
direction represent the outer and inner loops respectively. In simple terms, the
contours of layers are what the rapid prototyping machine works on as a basis. The
solid part is recognized as the left hand side of the contour and the positive direction
of the contours follow the counter clockwise direction. The model is ready for
processing and tool path generation once the solid part is identified.
2.2.4 Cutter path generation
Depending upon the rapid prototyping machine and software the part may require a
support material as a base over which the Actual part is made. Small machines like
Fab@home, Reprap due to their form factor have limited capabilities and so have to
be given the stl model of the support unit if the main model requires a base for its
existence. The tool path, which the machine will then use to build the model layer by
layer, is dependent on the user. Depending upon the requirement of desired
properties of the model in terms of surface finish, strength and build time the users
also have a number of options in tool path to chose from.
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