Spindle Fretting Repairs

That’s not rust on your tool holder; it’s fretting. Fretting of the spindle taper seat and/or tool holders appears as a rust discoloration. When magnified, you can see the material has been built up and removed in spots.

Spindle fretting occurs due to small, oscillating movements between the tool shank and the taper seat. The heat and vibration of cutting can cause this condition by micro-welding and removing material from the tool and spindle, resulting in fretting.

Conditions that lead to fretting include, but are not limited to, misfit of the tool and the spindle taper, low drawbar pull force, and contamination between the tool shank and spindle. Likewise, the overtightening of pull studs can cause deformation of the small end of the taper shank, creating a misfit for the tool to spindle connection.

Cleaning the tools with Scotch Bright or other abrasives may make the surfaces look better, but it will do little to help the issue and most likely create less contact between the tool and spindle, magnifying the problem.

New or reconditioned tools with a fresh spindle taper seat grind will cure the fretting problem and must be done. However, the underlying cause must be found out and addressed before or after a spindle repair. If the cause is a bad fit between the spindle taper seat and the tool holder taper shank, on-site spindle grinding can fix it. If it were contamination, grinding would fix it, but the cause of the contamination must be found and eliminated. Low draw force may mean the drawbar will need to be repaired. When having a spindle reground, the draw force will need to be checked and reported.

Our machine tool specialists can inspect, grind, and test your drawbar pressure. We can advise you of the probable cause of the fretting and alert you of any further action that should be taken to prevent fretting from returning.