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Pro/Engineer   March 2003   Tip-of-the-Month

## Dimensioning Curvature for Continuity

Curvature continuity can be a big deal in some applications, and Pro/E has several tools to help.  Here is a Sketcher trick pointed out by Paul Delong at a recent Pro/User meeting that can also help.

 Figure 1  -- Curvature Dimensions and Curvature Display.
Did you know you can dimension curvature at the end of a spline?

Figure 1 shows a sketch with a spline with curvature dimensions at the ends.  The dimension defines curvature of the spline at that point.

To make the spline curvature match that of the arc, the ends must be tangent (indicated by the T constraint), and the radius values must be equal.  By using the simple relation:

sd6=sd4/2   (radius conversion from diameter)
the curvature of the spline will always match that of the arc at the intersection.

To dimension curvature, simply enter dimensioning mode (Sketch > Dimension > Normal  -or-  select the dimension icon) then pick with the Left Mouse Button on the end of the spline (the end point will highlight).  Next, place the dimension with a click of the Middle Mouse Button.

 Figure 2  -- Surface Curvature Display.

With this additional curvature constraint some of the other options for controlling the spline (like Control Points & Control Poly) will be disabled.

To define the spline with a nice curvature, use the Display Curvature option in the Modify Spline dialog box.  The curvature graph is right on the spline as shown in Figure 1.  (Change the Density and Scale as appropriate.)

Proof of curvature is in the analysis of the final geometry.  Figure 2 shows a surface analysis after the above sketch was used for an extrusion.  The "Fuzziness" of the transitions is a good indicator of continuity.

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