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The Scheme example shows how to create a screw using sweeping with laws. One of the first steps is to create a center line for the screw. The center line is used by the
wire-body:offset command with a twist law option to create a helix. This helix then becomes the sweep path.
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A profile for sweeping is then created. The profile is a rectangle, resulting in an auger type thread. If the profile were a diamond or a triangle shape with the hypotenuse facing away from the center line, the result would be a v-shaped thread cut.
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The sweep options include a rail law to specify how the profile is to be oriented as it is swept along a nonplanar path.
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The profile is then swept along the helix path using the sweep options already established. After sweeping is completed, a cylinder blank is created. The threads can then be subtracted from the cylinder, leaving the auger thread screw.
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Scheme Example
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; sweep:law
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; Sweeping is much faster when the silhouette line calculation
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; isn't always performed.
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(option:set "sil" #f)
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;; #t
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; Create a center line around which to create the helix.
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(define wline(wire-body (edge:linear (position 0 0 0)
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(position 0 (law:eval "8*pi") 0))))
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;; wline
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(define path(wire-body:offset wline 5 "x"))
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;; path
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; Create a profile to be swept.
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(define p1(edge:linear(position 5 0 0)(position 8 0 0)))
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;; p1
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(define p2(edge:linear(position 8 0 0)(position 8 3 0)))
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;; p2
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(define p3(edge:linear(position 8 3 0)(position 5 3 0)))
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;; p3
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(define p4(edge:linear(position 5 3 0)(position 5 0 0)))
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;; p4
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(define profile (wire-body (list p1 p2 p3 p4)))
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;; profile; profile => #[entity 9 1]
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; Create a rail law to specify the orientation of the profile
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; as it is swept.
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(define my_rail (law "vec(-cos(x),0,sin(x))"))
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;; my_rail
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; Set up the sweep options.
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(define my_sweep_ops (sweep:options "rail_law" my_rail))
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;; my_weep_ops
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; Perform the sweeping using the profile, the helix path, and
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; the sweep options that specify the rail law.
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(define my_sweep (sweep:law profile path my_sweep_ops))
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;; my_sweep
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; my_sweep => #[entity 10 1]
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; Create a cylinder blank.
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(define my_cylinder (solid:cylinder (position 0 3 0)
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(position 0 (law:eval "8*pi") 0) 7))
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;; my_cylinder
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; my_cylinder => #[entity 11 1]
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; When the screw threads are subtracted (cut out) of the
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; cylinder blank, the result is a screw.
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(define my_screw (solid:subtract my_cylinder my_sweep))
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;; my_screw
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; my_screw => #[entity 10 1]
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; Render the screw to see the image as a solid.
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(render)
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Figure 1-9. Sweeping a Screw
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