Measuring spindle runout

Modified on Tue, 18 Jan 2022 at 11:21 AM

Measuring Spindle Runout

Overview

Spindle runout is a factor in machine cutting when the tool bit is not rotating as close to the theoretical axis of rotation as it possibly can. Below are two types of spindle runout:

Figure 1: Angular runout (left) and radial runout (right)

“Dial test indicator” Test

To test for this type of error, a simple test with a “dial test indicator” can be performed. Steps are listed below:

Load a calibration blank (or a broken bit with at least ¾ inch of smooth shank) into a collect and into the spindle. Make sure that the shank is properly mounted and is inserted at least ½ inch inside the collet.
Clean the exposed shank from any debris or dust that may have been accumulated onto it.
Mount a dial test indicator to a secure part of the table and position the ball tip of the indicator as close as possible to the center line of the shank and a bit further away from the spindle head as shown in figure 2.

$C:\Users\CANCAM\Downloads\Spindle straightness 2.JPG$

Figure 2: Mounting the dial test indicator

Adjust the position of the indicator stand until there is about 0.010in (0.025mm) of pre load indicated on the dial

Rotate the collet using your index finger to determine the orientation of the spindle that corresponds to the minimum indicated deflection. Note: the slightest pressure from your finger against the collet nut can give a false indicated deflection so remove it when reading the dial.
When you have identified the point of minimum deflection, rotate the “0” on the dial as close to the indicator needle as possible and mark this position on the collect to reference your starting position.
Rotate the collect nut one facet using your index finger. Remove your finger and read the dial. Continue until your determine the spindle orientation that gives the maximum deflection. Record this amount.

Alternate

The test below is another way to quickly see the runout of a spindle. This method is to obtain a rough picture of the amount of error when cutting.

https://www.youtube.com/watch?v=Sd5Zzy1nr-s

Causes of issues

Arrangement of the components of the tool/collet/spindle system
Uneven material density
Worn out spindle bearings
Poor collet to spindle coupling
Loose tool bits
Spindle motor resonances

References

http://www.precisebits.com/tutorials/spindle_runout.htm

https://www.youtube.com/watch?v=Sd5Zzy1nr-s