Page 112 - Mastering SolidWorks

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identifying Sketch entitieS 81

Figure 3.22
The modify
Sketch interface

would otherwise not allow it to be dragged (such as a collinear relation), you are prompted with
a choice to delete the existing relation and continue or copy the entity without the relation.
A sketch picture is a picture that is placed in the sketch, lies on the sketch plane, and is listed in
the FeatureManager indented under the sketch as a child. The sketch picture may be suppressed
independently from the rest of the sketch, and when the sketch is hidden, the picture is not
visible. You can easily move, resize, and rotate sketch pictures, as well as apply a transparent
background color to them. Sketch pictures are usually used for tracing over or as a planar decal
without the need for rendering.
The Equation Driven Curve tool creates a sketch spline driven by either an explicit or a
parametric equation, as shown in Figure 3.23. An explicit equation is in the form y = f(x), while
a parametric equation uses multiple equations driven by a common parameter value of the
form, such as
x = cos(t)
y = sin(t)
0 > t > pi

where t is a number in radians.
The result is a proportional spline in a sketch, not a curve feature as the name suggests. You
can drag the spline itself, or its endpoints, in 2D or 3D, and SolidWorks calculates the new
transformation. To reposition a sketch, use sketch relations and dimensions.
If you start an equation-driven curve in a 2D sketch, you get the form for a 2D curve equation.
If you start in a 3D sketch, you get the form for a 3D curve. After these splines are created, you
cannot remove the relation to the equation and manually edit the spline; they are tied to the
equation until you delete the entire spline.
One way to get around this limitation would be to create an equation-driven curve in one
sketch and then open another sketch and use Convert Entities to copy the spline, delete the On
Edge relation, and use Simplify Spline to add control points to it. This is a technique commonly
used with other types of curves; it does not enable you to update the overall size or shape of the
spline through the equation, but you can manually adjust sections of a curve originally created
from equations. Examples of where this might be useful would be a lead-in or lead-out on a cut
thread, a special attachment loop in the middle of a spring, or a flare around the edge of a lens or
reflector dish for mounting.