Hi,

I would like to ask some question about 3D sketch.

We can use TAB to select between XY, XZ, and YZ plane on which our cursor position will be positioned. However:

1. Can we **change origin**? If we have no way to change the origin, then no matter which sketch tool we choose (line, rectangle, arc, etc.), the first point that is projected into the selected plane upon our mouse-click is would ALWAYS LIE on the current plane. This means we have no ability to place the first point at an off-XYZ-plane location like coordinate (1,2,3), except if we move the drawn entity later.

2. Even with TAB toggling target projection plane, we are sitll limited to XY, XZ and YZ planes. This means that even if we have used "Reference geometry >> Plane" to create some **oblique planes **which are not parallel to any of the standard XY, YZ or YZ plane, we cannot make use of them in 3D sketch. Is it true?

3. I want to know if 3D sketch is a commended functionality or not? As Matt Lombard put in **SolidWorks 2011 Parts Bible**:

"Improvements have been made in the past several versions,but 3D sketches still lack some important bits of functionality"

"As a general caution, keep in mind that solving sketches in 3D is more difficult than it is in 2D. You will see more situations where sketch relations fail, or flip in the wrong direction. Angle dimensions in particular are notorious in 3D sketches for flipping direction if they change and go across the 180-degree mark. When possible, it is advisable to work with fully defined sketches, and also to be careful (and conservative) with sketch relations."

Mark's note seems to have some points in common with the two questions I asked above that there are limitations and certain control difficulties when working with 3D sketch. I wonder if 3D sketch is one of the primary tools in SW or not? By using "Reference geometry" we can get much more definite sketches than 3D sketch, so is "Reference geometry" preferred over 3D sketch?

Qi

It is easier if you think of a 3D Sketch plane as simple Sketch entity like a line or an arc or a spline.

A 3D Sketch plane has its own relations (again, like any other sketch entity). To prove that, create a 3D Sketch plane by any means and exit back to the 3D space. Now select the plane and you will see whatever relation it has.

The plane above was defined by 2 relations:

1. perpendicular to the line

2. coincident to the end point

That is all.. There is no Horizontal or Vertical relations assigned to it. It does not have an "orientation" from that point of view. Whatever line you draw on it, can get a local Horizontal or Vertical relation but that is just in regards to the plane. Since the plane is not fixed rotation-wise, the lines are not either.

Let's think of an real-life concept. You have a piece of paper on which you draw a vertical and an horizontal line. Now you take the paper and you stick it on a wall with a push-pin. The paper can rotate and the lines will rotate with it in regards to the wall. But the lines are happy because they think that they are still horizontal and vertical on the paper.

I guess, everything is relative, my friend.