Wednesday, July 27, 2011

Draw 2D Isometric Views

AutoCAD/LT allows you to simulate a 3D object from a particular viewpoint by aligning along three major axes by setting the Isometric Snap/Grid; however, although the isometric drawing appears to be 3D, it is actually a 2D representation. You cannot expect to extract 3D distances and areas, display objects from different viewpoints, or remove hidden lines automatically with this method of drafting.

When you create an Isometric drawing you are basically drawing "vertical" lines at 90 degrees with "horizontal" lines drawn at either 30 degrees or 150 degrees to give the impression of depth to the drawing. You start by setting the Isometric Grid and Snap using either of these methods:
  • The command SNAP, then selecting STYLE and assigning the style to ISOMETRIC.
  • DSETTINGS command's Snap and Grid tab (the Drafting Settings dialog box can also be accessed when you right-click on any status bar icon and choose "Settings"), under Snap Type, select Isometric Snap, and close the dialog:

Your Cursor will change shape: one axes remains vertical, the other aligns with one of the angles for  horizontal lines. The initial cursor mode is Isoplane Left: lined up with the left side of your isometric drawing. To switch to one of the two other isoplanes (Right or Top), you can use the F5 keyboard key or by typing CTRL+E to toggle between all three planes, or by typing ISOPLANE and picking Left, Right or Top. To draw circles with these settings, start ELLIPSE command and select the ISOCIRCLE option (need arc? Trim the Isocircles).

Creating Isometric Text and Dimensions are not so straight forward. First the Text, you must create two new text STYLES, the first with an Oblique Angle of 30 deg, and the other set to -30 (that's a minus-30 degrees). You would use each text style based on the location in relationship to your Isometric drawing, and alter the rotation angle of Text to suit:

Dimensions are the same: create two DIMSTYLES, one for each of the two text styles created above, and use DIMALIGNED command when drawing dimensions. You also must use DIMEDIT command's OBLIQUE option to assign a matching Obliquing Angle (30deg or -30 deg). You can do it all with one DIMSTYLE, but some users prefer the visual control of two, see example HERE.
If your dimension styles use arrows, you may need to also fix their appearance: explore this tip HERE.
While it takes many steps to create and set up the file to start drawing, consider taking the time to add these in Template file and reuse as often as needed. Give the two text styles and the two dimstyles unique but matching names to reduce the confusion of selection.