Menu : TRIM

Command: Blend:Free Form

Shortcut : None

This command creates a free-form blend between user-defined trim curves on two different surfaces.

The blend surface created by this command resembles part of the surface of a rubber ball rolling around the two surfaces. The blend surface is squeezed between the two surfaces and it joins the two surfaces tangentially.

There are several operations required to set up for this command. In general, you need to define a boundary Bézier curve (in some way) on each surface. There should exist one, and only one, such curve within the trim curve-set of each of the surfaces for the command to work.

There are several ways to create the boundary curves. One way is to first compute a rolling ball blend between the surfaces. Then change the trim curves to Bézier representation using CURVEÞChange:Approximate and edit the curves to a give a new boundary curve shape.

A second more general method is to use tool surfaces. A tool surfaces is an ordinary surface, created by any appropriate technique (extrude, rotate, build etc), which intersects one of the surfaces to be blended. This tool surface should then be TRIMÞIntersect:Surface with one of the blend surfaces to create a trim curve. After this operation the tool surface can be made inactive (or even deleted!) as it is not really part of the model. This operation can then be repeated with a second tool surface for the second surface to be blended.

The first two of the four diagrams below show the two tool surfaces in position. The third diagram shows the results of the trimming in readiness for the blend operation. The next step is to change the two trim curves to Bézier representation using CURVEÞChange:Approximate to a give a boundary curve shape.

Once the boundary trim curves are defined, the command Blend Free Form can be executed which will create the actual blend surface as shown in the fourth diagram above. There are two alternatives of how to compute the blend using rib control between the surfaces, or along curve length. Use the along curve length option only if the blend creation fails with the between the surfaces option.

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.

After the blend is computed, the system asks if the trim polygons should be calculated or not. Answer NO, if you already have the trim curve(s) existing as polylines, if you copied them before converting to Bézier curves otherwise answer YES.