Radial & Axial Runout Explained

In machining, runout refers to inaccuracies in a tool or piece of equipment that cause it to spin off its ideal axis. Spindle runout occurs when a spindle no longer rotates on its intended axis, which can result in:

  • Inaccurate machine registration
  • Issues with tolerance control
  • Excessive chip load
  • Poor part finishes
  • Insufficient tool life

Because of these risks, it’s recommended that you test your spindles for runout regularly and obtain necessary repairs as soon as possible.

There are two types of spindle runout: radial and axial. Both can lead to similar issues.

What Is Radial Runout?

Radial runout occurs when the axis of rotation deviates from the centerline axis of the spindle, but remains parallel. The amount of radial runout will measure the same along the length of the centerline axis.

What Is Axial Runout?

Axial runout occurs when the axis of rotation is tilted to some degree from the main axis of the spindle, so that the axis of rotation is no longer parallel to the main axis. The amount of axial runout will vary depending on where it is measured relative to the base.

How to Measure Runout

Spindles can be measured for runout while stationary (static) or operating (dynamic). In general, static tests are easier and less expensive to perform, but dynamic tests will give slightly more accurate readings while accounting for heat, vibration and centrifugal force. Both stationary and dynamic tests can be performed using multiple methods, which are detailed in the American Society of Mechanical Engineers’ Axes of Rotation standards (ASME B89.3.4-2010).

Using either a dial indicator or a non-contact sensor, technicians can measure both circular and total runout.

What is T.I.R.?

T.I.R. stands for total indicated runout. This is the difference between the maximum and minimum values measured across the entire rotating surface around a reference axis. T.I.R. can be measured using a dial indicator.

Be aware that there will always be a measure of runout present in any rotating tool, however minimal. Absolute alignment is not possible, but experienced technicians can return a spindle to its ideal alignment.

Correct Your Spindle Runout Today

If a piece of your equipment produces an uneven chip load or excessive tool chatter, you may be experiencing a degree of radial or axial runout.

The dedicated spindle repair technicians at Northland Tool can assess your spindle’s condition and rebuild it to the manufacturer’s tolerances. Send us a message or request a quote today, and we can get your spindle back up and running.

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