Inverse Kinematics Preferences

On the Inverse Kinematics panel of the Preference Settings dialog, you set options for both applied and interactive inverse kinematics.

Standard menu: Customize menu > Preferences > Preference Settings dialog > Inverse Kinematics tab
Enhanced menu: Customize menu > Customization > Preferences > Preference Settings dialog > Inverse Kinematics tab

Procedures

To prevent transforming unlinked objects while working in IK mode:

Open the Preference Settings dialog to the Inverse Kinematics panel.
On the Inverse Kinematics panel, turn off the option labeled Always Transform Children Of The World.
Single, unlinked objects are hierarchies of one object. An unlinked object is its own root and also a child of the world, so turning off Always Transform Children Of The World prevents you from transforming single objects in IK mode.

Interface

Applied IK and Interactive IK groups

The threshold and iterations settings are a trade-off between accuracy and speed. With the two groups of settings you can individually tune the behavior of Interactive IK and Applied IK. Interactive IK provides fast, real-time response, so you should set Interactive IK preferences for speed. Applied IK provides the IK solution to match the follow objects very closely. You should set applied IK preferences for accuracy.

Position: Sets how close the end effector has to get to the follow object or cursor position for the object to be considered a valid solution. The value represents a distance in the current display unit system. Small values increase accuracy but take longer to solve.
Rotation: Sets how accurately the end effector has to match the orientation of the follow object to be considered a valid solution. The value represents a rotation angle in degrees. Small values increase accuracy but take longer to solve.
Iterations: Sets the maximum number of times 3ds Max repeats the IK calculations to find a valid solution. A high iterations value increases the chance that 3ds Max can calculate a valid IK solution, but the calculation takes longer to complete.

Use Secondary Threshold: Compares the second derivative of the end effector to a very small threshold. If the derivative is within the threshold, IK is terminated.
Always Transform Children Of The World: Applies in both move and rotate modes when IK is on. It affects only an object that is a direct child of the world when the object is selected.
For example, if the root of an IK chain is a child of the world, and you're manipulating an object at the end of the chain (the root object itself isn't selected), 3ds Max observes any constraints set for the root object. However, if you select the root object and try to move it, its constraints will be ignored.