Video: Retention Knob Tightening And Toolholder Deflection

This footage illustrates how the toolholder taper is measured in a test designed to capture the retention knob’s effect on the shape of the toolholder taper.

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In a tapered toolholder, tightening the retention knob can produce deformation of the toolholder that can prevent the holder from seating properly in the spindle. J&M Machine offers a “high-torque” retention knob design that attempts to address this problem. This knob has threads that grip deeper into the holder, where the holder has more mass to resist deformation. This video, which the company produced, shows the toolholder deformation being measured for the high-torque and standard knob designs. The article under “Editor Picks” at right provides more detail.

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The Knob Problem

The retention knob is an unmistakably critical component of the machining process. However, the tightening of the knob itself can lead to the toolholder not seating securely in the machine. You may be losing tool life to knob tightness without even knowing it.