How to Control Precision with Object Snap Tools in AutoCAD 2014 - dummies

How to Control Precision with Object Snap Tools in AutoCAD 2014

By Bill Fane, David Byrnes

In AutoCAD 2014, a lack of precision makes editing, hatching, and dimensioning tasks much more difficult and time consuming. Controlling your precision can be a time saver as long as you keep these facts in mind:

  • Small errors in precision in the early stages of creating or editing a drawing often significantly affect productivity and precision later.

  • CAD drawings are often used for much more than giving pictures to someone. If the drawings have been properly created, they can also be queried for factors such as size, area, and quantity.

  • Drawings may guide manufacturing and construction projects; drawing data may drive automatic manufacturing machinery. Huge amounts of money, and even lives, can ride on a drawing’s precision.

In recognition of these facts, a passion for precision permeates the profession. Precision is one characteristic that separates CAD from ordinary illustration-type drawing work. The sooner you get fussy about precision in AutoCAD, the happier everyone is.

Drawing elements precisely refers to using precision techniques and tools to specify points and distances with as much exactness as the program allows. Luckily, AutoCAD provides a comprehensive package of tools for this task.

You can switch the display on status bar buttons between text and icons by right-clicking any of those buttons and selecting or deselecting the Use Icons option.

Technique Status Bar Button Label What It Does
Infer constraints INFER Applies geometric constraints at specific pick points (not in
Snap mode SNAP Forces the crosshairs to move on an imaginary grid of equally
spaced hot spots
PolarSnap Forces the crosshairs to move specific distances along polar
tracking angles
Grid display GRID Displays a nonprinting reference grid of lines or dots arranged
in rows or columns
Ortho mode ORTHO Forces the crosshairs to move horizontally or vertically from
the previous point
Polar tracking POLAR Causes the crosshairs to jump to specified angles
Object snap OSNAP Lets you pick specific points on existing drawing objects
without having to initiate a specific snap mode every time
3D Object snap 3DOSNAP Lets you pick specific points on existing 3D objects multiple
times (not in AutoCAD LT)
Object snap tracking OTRACK Causes the crosshairs to locate new points based on one object
snap point (or more)
Object snap overrides Lets you pick specific points on existing drawing objects one
time only
Coordinate input Lets you type exact X,Y or polar coordinates
Direct distance entry Lets you locate a point by moving the crosshairs to show the
direction and then typing a distance

Precision is especially important when you’re drawing or editing geometry — the lines, arcs, and other elements that make up whatever you’re representing in the CAD drawing. Precision placement usually is less important with notes, leaders, and other annotations that describe, not show.

To use object snap tools, follow these steps:

  1. Make sure all status bar buttons are turned off.

    They should have gray, not blue, backgrounds.

  2. Start the Line command.

  3. Pick three points to draw two sides of a triangle.

  4. Draw the third side of the triangle.

    Pick a point as close as you can to the start of the first line (that is, the first point you picked). Don’t use the Close option.

  5. Press Enter to complete the command.

    Pressing the spacebar is usually faster than pressing Enter.

  6. Right-click the OSNAP button and choose Settings.

  7. Deselect all items except for Endpoint and Object Snap On. Click OK.

    With these two settings, you’re turning on object snap functionality and one of the object snap modes (Endpoint).

  8. Start the Line command again.

  9. Hover the cursor over the first line so that a green square box lights up at the end of the line closest to its starting point. Pick the line at this point.

  10. Repeat Step 9 for the ending point of the third line, and then press Enter.

  11. Enter Zoom Object Last and press Enter.

    AutoCAD zooms in to display a tiny line segment — the last line you drew. The “triangle” now consists of four lines.

  12. Enter Zoom Previous.

  13. Repeat Steps 8–10, but select two lines that form one of the other two vertices of the triangle.

    Look in the command line, where AutoCAD reports that it created a “zero-length line”. Obviously, the two lines now touch perfectly because the last one “snapped” like a magnetic attraction to the endpoint of the first line. (Okay, it was the start point, but we’re sure that you get the point.)

    If you were able to make the first and third lines touch at the limit of AutoCAD’s 16-place accuracy, you should buy every lottery ticket you can find.

If you had tried to use the original three lines to control a computer numerically controlled (CNC) milling machine, you would have had problems at the final apex. You need to draw the triangle using the Close option of the Line command or the endpoint object snap.

Before you draw objects, always check the status bar buttons and set them according to your need for precision.

  • ON: The button looks lit (slightly brighter than its neighbors — typically, a light blue).

  • OFF: The button looks dimmed (typically, dark gray).