Transitional Recessed Surfaces
or Surfaces Transitioning to a Second Level

In this tutorial, I wish to go over the basics of what could be called a transitioned recessed surface,
or in other words - a cool looking indent on a surface that seems to come from nowhere.

You can't exactly use a Fillet to to make these rounded features, so the Blend command comes to the rescue.

Take note of these different elements:

Each of these elements can be straight or curved, as long as the basic elements are there.
(Excuse my lack of proper terminology or poor descriptions)

1) The "Threshold" curve is the exact area where the recessed surface becomes one with the main surface.
2) The "Outside" curve is the point at which the indent and the main surface meet. It should be a loop.
3) The "Inside" curve is the point at which you are now at the indented surface. It should be a loop.
4) The "Diversional" curve is used to make a reference surface by which to "peel" away the indented surface. It does not have to be a line.

Bear with me, you'll see what I'm talking about....

I need to Trim or Boolean Difference the Outside curve from the main surface:

You need to include the Threshold curve in the cut to form a complete loop.

Here is where you make the indent's surface:

The "Diversional Curve" needs to be extruded into a surface, so that a Blend command can be used on a tangent to form the "peeled away" indented surface.
It doesn't have to be a flat surface, you can use a Networked surface.
Make sure that the Blend to be produced envelopes (larger than) the entire loop area of the Inside curve to make the indent surface.

Here you make the blend:

The Blend is made from the tangent edges of both the main surface at the threshold point and the edge of the "Diversional" reference edge.
Note: This new "peeled away" surface can be either above or below the main surface - as long as it connects smoothly at the Threshold point.

Now take the Inside curve loop and Boolean Intersect that with the "peeled away" blend surface:

Delete the outer piece left over.

Here's where the magic happens:

Perform a Blend command between the edge curves of the main surface and the outer edge of the indent surface.


The picture on the left shows how a transitional surface is created (shown - is before trimming).  The picture on the right shows the elements involved in making that surface with Blend.

Thought it would be easy, eh?

The Blend command does a good job mating two surface edges, but the path of the edge side curves in the Blend are often wavy.
Now there is an overlap and a gap at this point of the Threshold area.

I'm going to cut out the bad stuff and make a new edge by which to blend the leftover part of the Threshold point to this new edge.
An Arc will work.

I just do a Boolean Difference to remove a small chunk of this uneven surface.

You'll have to add Trim points to the edge curves at these places:

Blend these smaller edges into a new surface:

Now the gap should be gone.

Now Join all these surfaces, and you should now have an interesting transitioned recess area.

Here is an example of what can be done on a curved surface:

This dryer model has transitioned recess indents on the side panels:
In a real life application, these areas would provide increased structural rigidity to the sheet metal panel, as well as a stylistic detail.

Here is a control knob that would be incorporated into the dryer model:

The knob body has a round shape that contains a pointer region, while a grip ridge sits on top that has a flat area for which to put type.
These features elegantly flow into each other.

I hope this tutorial comes in handy!