The following describes utilization of a non-contact force actuator to drive a machine-tool with a train of impulsive forces having a known, time-varying frequency to identify the speeds least likely to produce chatter (regenerative vibrations). It was prepared and written by J. P. Snyder of the University of North Carolina at Charlotte, M. A. Davies at the National Institute of Standards and Technology, J. R. Pratt at the National Institute of Standards and Technology, and S. Smith of the University of North Carolina at Charlotte.

The purpose of the device described here is to provide a simple, low-cost method for rapidly determining the most stable spindle speeds for a particular cutting tool/machine combination with no need for cutting tests. The simplicity of the device is possible because it does not attempt to determine the stable depth/width of cut; this must be determined by the machinist through trial and error. However, because of its simplicity, it can remain on the machine tool and should be comparable to a tool-length sensor in terms of ease of use. For this reason it is extremely suitable for use in smaller job shops where tool configurations (such as overhang) and hence stable speeds are changed to suit each new job.

As the market for high-speed machining grows the need for devices for stable speed determination will grow commensurately. A device such as this one would be extremely useful on machines since many of the modes of common machine/tool combinations have frequencies such that large stable regions are attainable with spindle speeds of 10 thousand rpm or more (for example, a two flute tool with a modal frequency of 1500 Hz produces stable large speeds at 11250 rpm, 15000 rpm, 22500 rpm, and 45000 rpm).

We estimate that with dedicated electronics, the device could be produced for less than five hundred dollars and could probably be marketed as an integrated option on a CNC machining center at a cost of two thousand five hundred dollars. It is likely that a relatively low-cost and robust sensor such as a microphone could be used in the device in place of the capacitance probe used in the prototype device.

The market for such a device could potentially be as large as that for other simple devices like tool-length sensors that are regularly sold on modern CNC machining centers. (References and details can be found on the full version located on the Internet per below.)

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