Boundary Surface Part 3: Tangent Influence

The Boundary Surface has a lot of options. I always ask for a lot of options, and I guess this is just a case of  ”be careful of what you ask for because you just may get it”. The interface also changes depending on what you have selected. I know there are people who think this is clever, but I for one mainly find it confusing. It means that you have to meet some preconditions in order to even see an option. For example, the Tangent Influence and Tangent Length settings are not available until you have set a Tangent Type of something other than None. Also, the Curves Influence options are not available until you have both Dir1 & 2 curves selected. Draft is not displayed until you have a curve selected, but in some situations is simply grayed out. Some of these options are labeled explicitly and some only with tooltips.

That leaves us with the following options which are initially hidden, and pop up as you select stuff:

• Curve Influence
• Tangent Influence
• Tangent Type
• Alignment
• Draft
• Tangent Length
• Apply to All

In this post, I am trying to limit discussion to Tangent Influence, Tangent Type, Tangent Length and Apply To All.

Also, I was wrong in the other post when I said that the Dir1 & Dir2 curvature combs are colored the same as the curve selection colors. It seems that the Dir2 curves and curvature combs are the same color, but the Dir1 selected curves are light blue while the Dir2 curvature combs are green.

These complaints are not meant to beat up this feature – it has become one of my good friends in many surfacing projects – but rather to get some of the points of confusion out of the way so we can talk about other stuff. Plus, in organizing the information maybe someone in Cahncuhd will understand these as usability or interface problems and take care of them.

Not holding my breath, but I say it with a straight face, and without a tinge of purple.

Tangent Influence is only active when you have set a Tangency Type to a curve, so something like Normal to Profile, Direction Vector, Tangency to Face or Curvature to Face. First of all, my Copy Editor at Wiley cringes when I rattle off the names of SolidWorks options. In this case SW combines options that start with “Normal” and “Tangency”. I can hear the Copy Editor screeching in my speakers now – “It is either ‘Normalcy’ and ‘Tangency’ or ‘Normal’ and ‘Tangent’”. Ayy! I guess it is a bit of inherited linguistic smugness. Not that I am all that when it comes to proper grammar. I still need a bevy of editors to follow me around to get things in the book correct. So what.

Some of the Tangency Type options are self explanatory and some are not.

None means that the surface direction at the selected curve is mostly influenced by the position of the second curve.

Normal to Profile means the surface direction at the selected curve comes perpendicular off of the sketch plane. Naturally, this is only available for 2D sketches.

Direction Vector means that you can use a plane, axis, temp axis, linear edge or sketch element to establish a direction. You could have a sketch on a plane, but want the surface to come off the sketch at an angle. You would use reference geometry such as a plane, axis or sketch to establish that direction.

Draft Angle can work with any of the settings, even Tangency or Curvature, even though it obviously breaks the tangency. That part of it may not make sense, but the Draft Angle option is a great one to have available. If it were not there, you would need to create angled ruled surfaces to start a boundary surface with draft.

Tangency to Face is only available when the selected curve is made of edges. If the edges have faces on both sides, there is another option called “Other Face” which allows you to switch the tangency from the face on one side of the edge to the face on the other side of the edge. I mostly use this for open surface edges, where there is only a single face. Remember the setting at View>Display>Tangent Edges As Phantom to get a quick visual check to see if edges are tangent or not (by “edges are tangent” I really mean “if the faces on either side of the edge are tangent to one another”.)

Curvature to Face is again only available when the selected curve is made of edges. In order to have curvature continuity (c2), the faces must first be tangent. So curvature continuity is a special case of tangency where the curvature of the faces on either side of the edge is equal. With tangency, the curvature on either side of the edge could be anything. There is no positive identifier for c2, you have to use visual techniques such as zebra stripes to identify c2 or the lack of it. (described elsewhere)

This brings us to Tangent Length. If you think of the material property of “stiffness” as being variable within an item, that’s what Tangent Length does. Tangent Length is the number 1.00 in the image above, and is also controlled by the silver arrow attached to the geometry. 1.00 is the default. Between 1 and 0, the material gets “less stiff”, and between 1 and 10 it gets more stiff. Smaller numbers bend more near the selected curve, higher numbers come off the sketch plane more nearly perpendicular. Below shows a Tangent Length of 2 for the same feature.

Next comes the Apply To All option. This refers to the Tangent Length option. This is another well hidden part of the interface. Apply to all what? Apply to all connectors, is I think the correct answer here. If you add connectors, additional Tangent Length arrows appear. If Apply To All is ON, then all the Tangent Length arrows are the same value. If it is OFF, you can change the length of the arrow at each connector, as shown below:

This is why they call this “advanced” I guess. It may be difficult to see what is going on here. I just made rectangles on offset planes, used them both as Dir1 curves, and assigned the Normal to Profile tangency type to one of them. Then I added connectors (by right clicking at a corner with the Selection Manager OFF). Notice in the image above that the edge that comes from the corner with the long arrow (lower left) has a big swoopy arc, and the one with the short arrow (lower right) is nearly a straight line.

Tangent Influence only appears when you have Dir1 & Dir2 curves. according to the Help, it is further only available when Global or To Next Sharp are used for the Curve Influence.  It only appears to make any difference if you have multiple curves in one direction. Here’s the example I am working with – a transition from rectangle to circle (Dir1) using a 3D spline as Dir2.

If the Tangent Influence slider is pushed to the left (smaller number), the boundary uses the circle shape for more of the surface. If the number is high, the curve with the tangency type set (rectangle in this case) influences the finished shape more, so the sides would be flatter. It seems to control the rate of transition between the curves.

I started this series of posts to show how easy to use the Boundary Surface is, and it is easy to use. But it is also very powerful. Part of the power comes in understanding all the petty options. The options are without a doubt confounding, but in the case where you need a subtle change in shape from what the default settings give, these options may turn out to be very important in achieving that last 5%.

Next time we are going to delve into the murky depths of Curve Influence.