AutoCAD

Autodesk's AutoCAD is a 2D and 3D computer-aided drafting application that is used across a wide range of industries by architects, engineers and designers. As of 2015, AutoCAD is in its twenty-ninth iteration and is the most widely used CAD program throughout most of the world.

AutoCAD may be different from any application you have used in the past. Instead of dragging-and-dropping, you will use the command line to create your drawings.


Image from Omura, George; Graham, Richard (Rick) (2010-11-09). Mastering AutoCAD for Mac (Kindle Location 669). Wiley. Kindle Edition.

All objects drawn in AutoCAD are placed on a simple X,Y coordinate system. In AutoCAD this is known as the World Coordinate System (WCS).

AutoCAD uses coordinates (x,y) to determine where an object is located. A line to the right of the the first point is on the positive X-axis. A line straight up from the first point is on the positive Y-axis.

A line has two points, a start point and an end point. AutoCAD works with the points to display the line on the screen.

Most of the time you will not have an indication of where the origin is. Often you will draw a new line starting from the endpoint of an existing line. To do this you use relative points. In order to tell AutoCAD that the next point is relative to the the previous point, you need to use the @ symbol (shift+2).

ABSOLUTE POINTS are exact points on the drawing space.
RELATIVE POINTS are relative to an object in the drawing space.



It's a simple system, but mastering it is the key to working with AutoCAD.

Angles are another important aspect to AutoCAD. But watch out, AutoCAD measures angles in a particular way:




In order to figure out the angle, you need to know that

• 0° is at the 3 o'clock position.
• 180° is at the 9 o'clock position.
• The angle between 180° and the line you want to draw is 150°.
• The length of the line you want to draw is 3 segments long.

With this information, you can figure out what angle you need.
Here's how:

1. Start at the 0° position and measure counter-clockwise (+) to 180°.
2. From 180°, measure clockwise 150° (-)
3. Consider that you just went +180-150 and use that as an equation: +180-150=30
4. Now you can draw your line by first creating a start point and then using relative positioning for the second point (polar coordinates):

   @segment_length<angle value
   

   or

   @3<30
   

You can specify points directly on the command line using three different systems:

1. ABSOLUTE COORDINATES—Using this method, you specify the points as they relate to the origin of the WCS. To specify a point just specify in the exact point as X,Y. So if you wanted to start the line 5 units to the right of the origin and 10 units up, you would type 5,10 and press <RETURN>
2. RELATIVE COORDINATES—This allows you to specify points in relation to the first point you have entered. After you've entered one point, the next would be entered as @X,Y. This means that AutoCAD will draw a line from the first point to another point X units over and Y units up relative to the previous point.
3. POLAR COORDINATES—You can use this system if you know that you want to draw a line a certain distance at a particular angle. You would specify this as @D<A, where D is the distance and A is the angle. Example: @10<90 will draw a line 10 units straight up from the first point.

Remember that X is always before Y. Don't forget the @ symbol when you are specifying relative points. Any typing error or omission will give you results you don't want. If you make a mistake and need to see what you typed, press F2 to bring up the command screen and check your typing. (press F2 to get back to your drawing.) If you want to undo the last point, type u and press <RETURN>

Basic AutoCAD Terminology

World Coordinate System (WCS)	This is the common X-Y coordinate system that is the default. If it is modified, it becomes a User Coordinate System (UCS)
Absolute coordinates	A way of inputting points based on AutoCAD's origin.
Relative coordinates	A way of inputting points based on a starting point.
Polar coordinates	A way of inputting points based on distance and angle.
acad.dwt	This is the default template that automatically loads whenever you start a drawing session. It can be customized to suit your needs. Templates are files that contains preset values for frequently used settings. The file extension is DWT.
Crosshair	This is your cursor when it is in the drawing space.
Extents	The outer boundaries of the objects you have drawn.
Grid	This is the pattern of dots displayed on the screen to guide you. It can be toggled on and off by pressing the F7 key.
Grips	Small 'handles' on objects that allow for quick editing.
Layer	All objects are drawn on a layer. You can group objects on a single layer or create multiple layers in order to better organize your drawing.
Linetype	All objects are drawn with a particular linetype. Examples would be solid, center, dashed, etc.
Object	Any item that is in the AutoCAD database. Also known as an entity. An AutoCAD drawing file is actually one large database containing all the information needed to reproduce the objects when the file is opened. Information for layers and linetypes, are stored in this manner.
Origin	The (0,0) point of your current coordinate system.
Orthographic mode	This is a drawing mode that allows you to draw only perpendicular lines. It is toggled on and off by pressing the F8 key.
Osnap - Object Snap	This is a method of 'snapping' to certain, precise points on an object. This might become your best friend.
Pan	To move around the drawing by dragging the drawing area around your screen.
Panel	A grouping of commands on the ribbon. The Ribbon runs across the top of the drawing space and contains panels - each panel has a group of associated tools. Switch to different panels by clicking on the tabs at the top of the ribbon. (PC only).
Selection set	The current group of objects selected for modifying.
Units	The basic drawing unit set for your drawing. You can use inches or millimeters depending on your needs, but if you are modeling for Desktop 3D priting you should only use millimeters. You can also set the precision that you want displayed.
View	A particular area of your drawing.

AutoCAD does have a tool palette, but you will find that with practice using just the command line will allow you to work much faster.

AutoCad Setup

When using the Command Line, AutoCAD expects you provide information in a very particular order. As you enter information you will see that the command line will provide prompts for the information that the program requires to continue. Watch the command line and follow the prompts.

You do not have to place the cursor in the command line field. Just start typing and the text will appear in the field. If you need to get out of a command, press ESC.

1. Launch AutoCAD.
2. Create a new drawing. Select File>New Drawing:
   
3. Select acad3D.dwt template file and press the Open button to continue to the drawing screen.
   
4. Find the commandline.
   
   
   
   If it is not present you should be able to open it it by selecting Window> Command Line
   
   
   Other ways to display the command line are:
   • Pressing Command+3 on Mac, CTRL+9 on Windows.
   • Pressing F2
   •Typing COMMANDLINE or CLI
5. You want to set your units to millimeters. Type UN and select UN (UNITS):
   
   
   or select Format>Units from the top menu to bring up the Units Dialog box.
   
   Set your units to millimeters:
   .
6. You want to create a resolution appropriate for 3D printing. Type FACETRES and set it to 10.
7. Make sure your profiles are not deleted after you use them. Type DELOBJ. Set the value to 0.
8. In the top left corner set the Custom Visual style to Wireframe or Shaded with Edges.
9. Autodesk, like Photoshop has layers. Type LAYER (LA) to initiate the command
   or select Window>Layers or press Command+4 (Mac):
   
   
   This will bring up the Layer Properties Manager Palette:
   
10. Click the New Layer Button.
    
11. Name the new layer center hub (press <RETURN> after typing the name in the field).
12. Type Properties or PR to open the Properties Inspector
    or select Window>Properties Inspector or press Command +5 (Mac)
    
13. In the Properties Inspector make the layer's color white:
    
14. To move objects to a particular layer, select your object or objects or drag a box around them (if you drag from left to right (→), your selection must include every line. If you you drag from right to left (←) you just need to include part of every segment). Look for the Layer Properties Manager Palette. There is a drop-list there with your layer names. With your objects selected, change the layer to object.
    
    
    Press the ESC key. If all went well, your object will now be on the selected layer.
    
15. To close the Properties Inspector type PROPERTIESCLOSE.
16. To save your drawing type SAVEAS and save your drawing either in your work folder or on the desktop. Make sure to name your drawing so that you can find it later.

OSNAPs

If you want to draw a line from the CENTER of a circle to the middle of a vertical line, AutoCAD has a feature that makes this very easy. The feature is called Object Snaps (or Osnaps pronounced "Oh-Snaps").


Image from onikage108.deviantart.com ©2011-2015 katarnlunney


There are a few ways to enable OSNAPS. First you can type OS and press <RETURN>. You will see a dialog box:


You may select whichever points you want to 'snap' on an object.

Another way is to enable OSNAPS is using the status bar. CTRL+click on the Object Snap icon and then select the OSNAP/OSNAPS you want to enable.
.

OSNAPS are on when the icon is enabled:
.

Another way is to press F3 for 2D OSNAPS and F4 for Object Snap Tracking . Object Snap Tracking works with OSNAP and POLAR to help align new points with existing locations in your drawing.

You can also select the OSNAP using the command line.

Export

1. Type EXPORT and press RETURN.
2. Select STL as the type of export.
3. Name the STL file.
4. Click on your model when prompted to select solids or watertight meshes.