Single Point Threading Adds Strength to Retention Knobs
April 1, 2025
Retention knobs are subject to a lot of stress and force when in use, and the threads play a key role in keeping the workpiece firmly gripped. T.J. Davies forms its retention knob threads using single point threading to Imperial (Class 2A UNC) or Metric (Class G6) standards. This helps ensure that the threads are balanced (lead-in/lead-out at 180°) and that full depth is attained for each thread. Attaining full depth provides them with a firmer grip, which holds the tooling securely without vibration.
"Rolling is an alternate means of forming threads; this effectively squashes the steel to form the threads, but only to a shallower depth," said a company spokesperson. "This shallow depth introduces some play between the retention knobs and the holder, thus transmitting vibration through the knob, which weakens it. In addition to vibration, rolled threads can cause wobbling and misalignment, which can damage the spindle. With enough spindle damage they can snap, causing damage to the workpiece and potentially harming employees. Single point threading eliminates these potential problems and extends the service life of the retention knob. T.J. Davies manufactures the industry's broadest line of retention knobs, with many available for same day shipment."
T.J. Davies manufactures every retention knob using American-made 8620 alloy steel that is then machined in-house in a single set-up to help ensure concentricity. The use of 8620 means that the components will work harden over time, rather than becoming brittle as is the case with retention knobs machined from 9310 alloy steel.
After threading is completed, each component is heat treated to 58-62 HRC and then treated with hot black oxide to military specifications for protection against corrosion. Each retention knob is magnetic particle tested and then pull tested to 2.5x the pulling force of the drawbar for which it is designed. Certifications maintained for each step and each batch provide traceability and quality control.
In addition to the 500 plus styles available, T.J. Davies has an in-house engineer who can make custom knobs for older machines that are no longer made.
For more information contact:
T.J. Davies Co., Inc.
11823 Ohio Route 44
Mantua, OH 44255
440-248-5510
sales@tjdavies.com
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