Confusing concepts in CAD

There are some similar concepts in CAD and it’s easy for some newbies to get confused, so I’ve listed some of those concepts below.

1.Zoom & Scale

Zoom (Z): Zoom is about the viewport, not the object itself. It’s like the lens of a camera and you can see things closer or farther with Zoom. Although what you see is a bigger or smaller object, the real size of the object won’t change anyway.

Scale (SC): Scale is about the object since using it will change the actual size of the selected object. Using Scale, you need to specify scale factor and the object will be scaled according to the scale factor.

2. Stretch & Extrude

I think these two are less confusing since Stretch is usually used while Extrude is less used by designers. But we still need to tell one from another.

Stretch (S): Stretch is to extend parts of 2D objects. Usually, it’s used to modify the size of parts of the object in a certain direction; if the whole object is selected, then the object will be moved.

Extrude: Extrude is to extend 2D graphics into 3D models and you can use it on polyline, area and so on. It works like this: Draw the section of the 2D graphics and process it into polyline or area, specify the height of extrusion, we can also specify the angle of extrusion.

3. WCS & UCS

Those two concepts are not complex though confusing for many starters. CAD system has provided us a virtual three-dimensional space and this three-dimensional space has a coordinate system as its benchmark and this coordinate system is called WCS (Word Coordinate System). Users can change the coordinates-origin, direction, rotation angle, and position, the coordinate system after all these adjustments is called USC (User Coordinate System). We can define and change UCS, but the WCS is unchangeable.

4. LTSCALE, CELTSCALE & PSLTSCALE

LTSCALE: Line type of all the graphics in the drawing will multiply this figure, for example, if we set the LTSCALE as 100, the line type scale of certain line is 2, then the actual scale is 200. If the drawing file size is very large or small, we can adjust LTSCALE in order to normally display the dashed line.

CELTSCALE: The CELTSCALE in the linetype manager will affect the linetype of all already-created objects but will not affect those that have been created.

PSLTSCALE: Every object has its own linetype and we can modify it in the Properties box.

5. Drawing scale, plot scale & viewport scale

Drawing scale: Drawing scale is to zoom in and out the drawing according to certain scale, for example, if the drawing scale is 1:100, this is to zoom out the graphics 100 times to ensure the drawing can be plotted by 1:1 scale, in this case, we need to dimension according to the actual size and set the scale of dimension.

Plot scale: Drawing by 1:1 can make the drawing very big or small, we’ll always need to zoom in or out by some scale to make it printable, so we need to set the plot scale. Usually, the plot scale has already been set before drawing.

Viewport scale: CAD provides layout space printing. We can use a viewport to display drawings, set the viewport scale, add drawing frame to the viewport, and print by 1:1. Multiple viewports can be set in the layout space and every viewport use a different scale, in this case, we’ll need to adjust the text and standards.

6. Thickness and Elevation

When drawing rectangles, two parameters appear in the Command line: Thickness and Elevation.

Elevation is the flat space where the rectangle is ( other flat spaces parallel to space whose height is 0, and its height shows in its z-coordinate)

Thickness is about the rectangle itself, more specifically the height that forms the cube( we can see this in 3D drawings)

In the following picture, there are three rectangles, the thickness of the red and green rectangle is 0, the yellow one 30, their elevation is respectively: 0, 50 and 100.

Thickness is an attribute of two-dimensional drawing while elevation can be applied to every separate object as well as to viewport as a whole.

Thickness: Open the Properties box with CTRL + 1, we can see that thickness is a basic property. We can set thickness with most two-dimensional graphics such as line, polyline, circle and so on, but spline is an exception.

Elevation: If the z-coordinate of the graphics that you’re drawing is nonzero, it means that your current drawing has elevation. If you open the Properties box without selecting any objects, take a look at the z-coordinate of the viewport. If you can’t modify in the Properties box, you’ll need to enter Elevation command and modify the elevation.

OK, that’s pretty much I’ve concluded and if you have concepts that just drive you crazy and you can’t tell one from another, please leave a comment or email me, I will add them to the list.