In traditional parametric-based environments such as Inventor or Solidworks, sketching typically involves defining a “New Sketch” which is aligned to a face of the 3D model or with reference to the world coordinate system. Every object drawn on this sketch will be coplanar and drawing out of plane requires an entirely new sketch definition. As such, every consecutive “New Sketch” exists separate from other sketches and its objects cannot interact with those from a different sketch.
This is not the case with BricsCAD, where sketched objects exist globally and are not grouped by their planar references. This allows any two sketch objects to be connected and used together. This flexibility is great, but we still need a plane to draw our sketch on. This is where we need to use BricsCAD’s flexible, easily configurable Dynamic User Coordinate System, or DUCS for short.
When sketching in BricsCAD, your curves and polylines are drawn in the XY plane of the user coordinate system, with the Z-coordinate of the point you clicked on replaced with a pre-configured Elevation value. The primary function of DUCS is to quickly reposition those axes to allow sketching in different orientations.
DUCS works by temporarily aligning the XY axes to a flat face of your 3D model when you hover over it while a sketching command is active. Once the first point is in place, the coordinate system is locked and you are free to place additional points, which will be coplanar. When the command finishes, the UCS returns to the default world orientation.
Using DUCS can be a bit tricky at first, especially if your model has many flat faces. Since DUCS becomes active when you call a sketch command, it can be difficult to get it to align to the correct face. To avoid this, be sure to zoom in on your sketch face before activating a command, after which you can zoom back out. If you need to sketch coplanar to a face, but away from it, use the Shift key to lock down the DUCS orientation before moving your cursor off the face.
You can also use DUCS to sketch on any curved surface. If you mouse over the side of a cylinder or a sphere with DUCS active, the first click you place will lock down the UCS so that the X and Y axes are tangent to the surface at that point. Any new point will be coplanar to the XY plane of this UCS. If you don’t want to start your sketch at that point, you can use the shift key to lock the UCS before placing the first point.
As useful as DUCS is, there comes a time when you need to turn it off. For example, if you are placing many sketches on a single face, locking down DUCS every time you run a new command can get very tedious. In this case, turning DUCS off and manually realigning the UCS to that face can avoid you the extra hassle.