Menu : TRIM

Command: Blend:Rolling Ball

Shortcut : None

This command creates a rolling ball blend between the target surface and another surface, which must intersect. In addition, it trims the surfaces where the blend touches the surfaces.

The blend surface created by this command resembles part of the surface of a ball rolling around the two surfaces. The blend surface has a constant radius, circular cross-section and it joins the two surfaces tangentially.

For this command, the target surface is called "this surface". The second surface is called "other surface".

Normally pointing and clicking with the left-hand mouse button after executing the command indicates the other surface. Sometimes it may be difficult to point exactly at the surface that you want. The alternative way is to click any key on the keyboard, which brings up a dialogue box in which the name of the element where the surface is located and the number of the surface is entered.

Before computing the actual blends, the program computes the intersection(s) between the two surfaces. If there are several intersections DeskArtes displays numbers on each intersection, and asks for which intersection number you wish to calculate the blend.

The command next displays a series of arrows on the two surfaces that will be used to indicate which blend surface is to be calculated.

A parameter box is then displayed requesting the radius of the blend and the direction of the blend. Choosing whether the ball will be rolled on the side of the surface pointed to by the arrows (normal side) or the opposite side (opposite side) indicates the direction. This needs to be indicated for both surfaces giving four possible combinations (normal-normal, normal-opposite, opposite-normal and opposite-opposite) producing four possible blends as represented below.

If the intersection does not form a closed loop, it is called an open intersection and the system also asks where the blend should terminate. The options are at the trim curve or from the edge of either of the surfaces. Thus, it is possible to extend the blend outside the actual surfaces.

After entering these parameters DeskArtes calculates and displays the blend. If the blend is satisfactory it can be accepted, if not reject the blend. If you reject the blend, you will have the option of changing some of the parameters and recalculating.

If there were multiple intersections, the command cycles through the above operations allowing you create blends at each intersection if required. Notice that you can change the directions, and use different radii for different intersections.

The calculation of the blend is a mathematically very complex operation.

Note: Unlike surface intersections, blends cannot be computed over sharp corners. They should be redefined with small round corners before blending.