Everyone is (or should be!) familiar with linear and circular patterns. But how would you make a pattern that doesn’t follow a straight line or a circle? Curve Driven Patterns is the answer.
The first example is an end plate for an oddly shaped pressure vessel. The task is to place a number of evenly spaced bolt holes around the perimeter and offset from the edge. To start, make a sketch offset from the edge with one Hole Wizard hole placed coincident with the sketch.
Then make the pattern using Insert>Mirror/Pattern>Curve Driven Pattern. Select the sketch to guide the pattern, select the feature to pattern, enter the quantity and check “Equal Spacing”. In a real design exercise, you would use the pressure and area of the plate to find the force, and then use the tensile strength of the desired fastener and a factor of safety to choose the quantity.
Curve Driven Patterns are even more useful when the pattern doesn’t lie on a planar surface. This example is a stamped sheet metal rib for an airplane wing. After the stamping operation, rivet holes are drilled in the flange to attach the skin. We want each rivet hole to be perpendicular to the flange and equally spaced. A sketch (in red) is made by converting entities of the airfoil sketch on an offset plane and a rivet hole is positioned at the end of the sketch and perpendicular to the surface.
When the pattern Property dialog is open, check the box for “Tangent to Curve” and finish the pattern. Notice how each hole is aligned perpendicular to the surface of the flange.
Straight lines are curves, too. Placing a series of scalloped cuts on the straight edge of this part can be done with a linear pattern, but this requires measuring the length of the edge as an input to the linear pattern, and it requires calculating the spacing to make the pattern finish at the other end. A curve driven pattern can do this without the measuring and calculation, and it automatically updates when the length of the edge changes, while the linear pattern requires a new measurement and calculation.
In this example a linear pattern on the top edge starts with a hole shown in red. A curve driven pattern on the bottom edge starts with a green hole. Both patterns get the same equally spaced result.
Then we edit the base sketch to make the part longer. The curve driven pattern takes advantage of the “Equal Spacing” option to correctly space the holes. The linear pattern will require editing to recalculate the spacing.
