Understanding AutoCAD Mechanical Object Snap Settings



February 12, 2013

From: John Hackney



IMAGINiT Tricks Tutorial: Have you ever felt like your instant items were possessed? If you encounter strange behavior while using them, this trick may help you.

Editor’s note: This tutorial is courtesy of IMAGINiT Technologies.

AutoCAD Mechanical has a truly wonderful set of commands and settings that make it a superior tool for CAD work. There are times when some of these settings can confuse the best of us, unless we understand the program’s option settings. In the image below, you can see that I haven’t enabled object snaps and haven’t selected any.

When I launch the Line command and move between objects on the screen, I see object snap markers. At this point, two possible thoughts arise: “I did something wrong in the configuration of the program” or “The program is not working correctly”.

AutoCAD Mechanical provides two methods for assigning snaps to objects: system settings and user settings. If you are experiencing strange behavior when using object snaps, the system is probably set to the system settings method. The Line command is configured in this method by the program to automatically impose certain object snaps. The good news is that you can configure these system object snap controls, and you can revert to full user control if you want. Once you figure them out, you’ll probably configure them to your liking and leave the system settings enabled.

To find out which setting is used for AutoCAD Mechanical object snaps, open the Options dialog box. My favorite way to access this dialog is to right-click on the command line. Once there, navigate to the last tab on the right, which is titled AM: Preferences. In the Snap Settings drop-down menu, you’ll see which method is currently in use and how to change it. At this point, make sure it’s in the system settings so we can see where the “automatic” object snaps are coming from.

The next selection will make a lot of users uncomfortable, because the settings are in the code rather than in a user-friendly dialog. Take a deep breath and select the System button, which is below the Snap Settings drop-down menu we just used. In the resulting dialog box, expand the two levels shown and highlight the [email protected] entry. You’ve probably guessed already that this section controls which object snaps are assigned to various program commands.

I need to present a short refresher lesson on how object snaps are assigned using the OSMODE system variable. If you type Sysvdlg on the command line, you will see the System Variables dialog box. Select the OSMODE variable to display possible numeric setting information. Please pay particular attention to the text described in the graphic below on the method for assigning multiple snap modes to objects. We will use these numbers to configure which object snaps are active when an AutoCAD Mechanical command is executed.

AutoCAD Mechanical has three unique Power Snap parameters, shown below with their assigned system variable values.

Then, back in the System Editor, scroll down to the Line command on the Osmode4Cmds entry. The entry in my example is +39|4 but yours will probably be different. I think a fresh install of AutoCAD Mechanical has a value of -39.

The format of this value is as follows: Sign opt ACADSNAPMODES opt DELIMITER opt MCADSNAPMODES

  • Sign: The minus or plus sign. A minus sign activates snap modes set by ACADSNAPMODES or MCADSNAPMODES and those set in the Drafting Settings dialog and the Power Snap Settings dialog, when using the corresponding AutoCAD command. A plus sign enables snap modes defined by ACADSNAPMODES or MCADSNAPMODES and disables them in the Drafting Settings dialog box and the Advanced Snap Settings dialog box.
  • Opt: You can omit the following section.
  • ACADSNAPMODES: AutoCAD object snap mode value code based on the AutoCAD “OSMODE” system variable.
  • DELIMITER: The pipe sign “|”
  • MCADSNAPMODES: Value code for AutoCAD Mechanical object snap modes: Radial Arc (1), Tangent Arc (2), and Mirror (4).

The value is changed by right-clicking the key value and selecting Edit.

Using the rules above, the object snap settings (which automatically turn on when you run the Line command) will be Endpoint (1), Midpoint (2), Center (4), and Intersection (32) from ACADSNAPMODES (39) and MCADSNAPMODES Symmetry Power Takeoff (4). The most preceding the number will disable all other object snaps set during the command and re-enable them when the command completes.

A final setting will help you monitor which object snaps are enabled when executing various commands. In the Power Snap Settings dialog, check the “Show snap in status line” option for all four Power Snap configurations.

As you select various commands, automatically or manually assigned object snaps appear in the status line.