When a surface loft just won't work...

In years past, modelling items such as lofts, sweeps, and fillets were used as a benchmark for how good a 3D solid modeler was. As things go with technology and time, these items become less and less different from CAD package to CAD package (BUT, believe me, some packages are better than others).  Fillets, for example, are well-achieved by most of you major 3D solid modelling packages.  And what about lofts?

You do know what a loft is, right?  A calculated and approximated blend between two or more contours.  In the case of SolidWorks, closed contours can be used to create a solid loft and open contours can be used for a surface loft.  Either way, HOW you control the blending between profiles/contours makes a difference.  And this difference can affect the final look of the blend.  To further tweak the shape of either a lofted or a swept feature, you can add "guide curves" that push and pull the blend along the direction you choose. These curves are either 2D or 3D sketches.

SolidWorks has increased the ease of use of lofts by adding curvature and tangency control as either a start or end contraint (or both). See the picture below. This is wonderful news... until you start adding guide curves.  With the addition of guide curves, the shape gets pulled and stretched.  And while tangency or curvature is being controlled AT THE BOUNDARIES of the profiles, it is not neccessarily being controlled along the guide curves.  Let's look at an example of such. Here, we are lofting between the brown shape to the green shape and will control it with the two blue splines you see in the picture below. The resulting loft is also pictured below.

In order to control tangency or curvature continuity in both directions, instead of a loft you can try the new surface tool Boundary Surface. The control panel is pictured below.

For Direction 1, the profiles are chosen. Direction 2 can be considered the guide curves. Therefore, both directions are considered and controlled for the surface creation. The resulting surface is also pictured below. You can click on any of these images to make them larger.

In most cases, a boundary surface produces a nicer looking surface. Play with it. Give it a shot.  And leave us feedback here on SolidNotes if this has been a useful new tool for you.

Comments

[Gavin]

I read your artical and was wondering if I can use this technice with routing air lines and wires.

[Christopher Schaefer]

Gavin,
While not entirely sure by what you mean when you write "routing with air lines," the baoundary surface tool is a surface-only command and, as such, does not relate to SolidWorks Routing. The guide curves used in the sketch used for this command can not be used as a Route path; the curves used for "Direction 2" in the Boundary Surface command must all come from the same part and, therefore, the route sketch is unavailable.

Thanks,
Chris

[Johnny Rocks]

Yo Dawg,
How many guide curves is to many?

Johnny

[Chris]

Johnny,
See personal reply sent to your e-mail address.

[Roland Ellis]

Chris,
some help please !

what I'm trying to do:

3 planes (0%, 50%, 100%) along a 3d Curve that is editable by 3d sketches of two plotted points.
sketches (closed loops) on each of the planes of a tapering "L" shape, with the same point on each sketch sitting on the guide curve.

I have been trying for a while now to get this to loft however it is proving problematic!

I tried your Boundary Surface but It would not resolve because it said that it
would interfere with it's self (number of sketch points? like it said it is tapering)

If I have more planes and sketches then editing the form is very complicated
If I add more guide curves, point to point along the sketches, they do not follow the form of the guide curve.
adding all guide curves that I specify the coordinates of is unworkable!

maybe you could just run though how you would go about this type of form, as i may be making some rookie mistakes !

Many thanks
ro