We ID guys use them often for creating more complicated geometry. You
can use them to create complex curves in space (intersecting extruded
surfaces) and many other things, such as surface offsets for stopping
cuts or extrusions. If your world is primarily planar, there's not much
need for them.
Industrial Designhaus, LLC
Without going to swoopy stuff, surfaces have their uses, and are
One example where surfaces are useful, even in prismatic design:
Take, say, rectilinear gearbox housing for worm reduction boxes.
Say you have cooling fins on a face of the box, which are "cut extruded"
across to a couple of upstanding faces, perhaps including an output bearing
boss. An "Up to Surface" cut extrude will only allow you to pick one face.
If you need the extrude to terminate at a collection of faces, pick those
faces and "Insert/Surface/Knit"
(Some old hands may not realise it is no longer necessary to first convert
those faces to surfaces, by offsetting zero: Knit will automatically convert
a face to a surface)
Then, when you come to specify the extrude "Up To" surface, pick the
"Surface-Knit" feature from the feature tree.
I should have mentioned:
If you get unpredictable results from the extrusion, check that you've
picked ALL the faces the sketch projects across. It doesn't matter if you
pick adjacent faces which are not currently capping the extrusion, in fact
if you are designing a model which will represent several different sizes of
gearbox (in the example I gave) you should err on the generous side.
Surfaces are great for modeling swoopy stuff, but that is not their only
application. In fact, from the first day you started working on SolidWorks
you've been modeling with surfaces. Solid modeling just automates a lot of
functions that change that underlying surface model into a chunk of stuff.
What does it mean for you? Well, solid modeling creates lots of hidden
faces in the model that you don't really need. For instance, if you us a
rectangular cut to shave a model back, you actually are creating six faces
inside the modeler to get the one you want in the model. Using surfaces,
you can make that sort of thing directly, using only one face. I am not
saying you want to do this with every cut, and of course using a solid cut
with an open contour also streamlines the face count. But have enough
features in the model (or a slow enough computer) and all that extra stuff
that you don't see can add up (I've actually run some tests).
There are all sorts of other little things that pop up here and there where
its just faster and easier to convert the model to a surface model (delete a
face without patching it) then going back to a solid later, or use a surface
to swap one undesirable face for a better one. And this is on stuff that's
not particularly curvy. Surfaces are also really handy for repairing all
those weird little glitches that can pop up when a cut goes too far or
something doesn't quite line up like you want it, or you want to test a
radical change to a model but don't want to deal with your feature tree
erupting in blood.
If you are in the Texas area, I am going to head down to the all Texas user
conference in July and give a talk on just this subject. Its called
"Surfacing for 'Block-heads" and will try to answer just your question -
what are surfaces and are they ever really useful?
This session will go into how SolidWorks operates behind the scenes, and
explain how that knowledge can get you through modeling challenges and
streamline the creation of all sorts of parts. The first half of the
presentation will cover the BREP, the interchangeable use of Solids and
Surfaces, and deconstruction of features into their behind-the-scenes
processes. The second half of the session will show how this information
can apply even to those folks who suspect that surfacing has no place in
If you ever have problems filleting, you will be very happy you came.