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T.J. Davies Retention Knobs Maximize Cutting Tool Life

Custom-made retention knobs are sized to fit the machine tool and spindle or toolholder to extend the life of existing machine tool assets.

Chris Pasion

Managing Editor, Modern Machine Shop | Production Machining

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Retention knobs
Photo Credit: T. J. Davies Co. Inc.

T.J. Davies Co. Inc. makes custom retention knobs, pull bolts and other workholding components and accessories to fit older or obsolete machinery. All dimensions of the knobs can be customized, including length, diameter, thickness of collars, dimensions between collar and knob end, thread size and more. Additionally, customers can specify a coolant hole, taper style and whether O rings are required. Custom-made retention knobs are sized to fit the machine tool and spindle or toolholder to maximize the toolholders performance and cutting tool life, and extend the life of existing machine tool assets.

All T.J. Davies custom retention knobs are manufactured from American-made 8620 alloy steel, which has a high-tensile strength to withstand strong centrifugal force, high load force, high feed rate and difficult-to-machine material. All knobs are machined in-house with single-point threading to imperial (Class 2A UNC) or metric (Class G6) standards. After threading is completed, each component is heat treated to 58-62 HRC 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 it is designed for.

According to the company, the use of 8620 ensures that the components will harden over time, rather than becoming brittle, as is the case with the use of 9310 alloy steel. Single-point threading ensures that the threads are balanced (lead-in/lead-out at 180 degrees) which is very difficult to achieve when rolling threads. Full depth is also attained for each thread. Because all machining is done with a single setup, concentricity is achieved.

Each component is heat treated to a case depth of 0.020 to 0.030. No carb is applied to coolant through hole to ensure there is no shrinkage. Core hardness of 40HRC is standard. All retention knob surfaces (not just mating surfaces) have a precision finish of 32 RMA micro or better, ISO grade 6N. Certifications are maintained for each step and each batch to ensure traceability and quality control.

T.J. Davies provides recommended torque guidelines with each retention knob. Sockets for the proper installation of retention knobs are available, individually or as a complete set of four.

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