Performance Evaluation of a Prototype Machine Tool for Machining Meso-scaled Parts Brad Damazo, Alkan Donmez, Michael McGlauflin and Johannes Soons National Institute of Standards and Technology S. Chad Bryant, University of North Carolina Charlotte Jaime Werkmeister and Alexander Slocum, Massachusetts Institute of Technology Abstract With the increased prevalence of meso-scaled products and feature sizes, new tools are needed to bridge the gap between fabrication processes tailored for micrometer sized features and those for millimeter sized features [1-4]. Compared to its traditional counterpart, a small machine tool designed for meso-scale parts has the advantages of: ease of use, smaller footprint, smaller structural loop, shorter distances between the workpiece and the machine’s metrology devices, opportunities for improved machine metrology, and easier environmental control. At the same time, the small work volume presents a challenge when measuring the machine’s geometric errors, as traditional machine tool metrology instruments (i.e. lasers, ballbars, levels, etc.) are difficult if not impossible to use in very small work volumes. This paper describes a prototype three-axis meso-scale machine tool that has been built and is configured for rotary milling applications. In addition, preliminary performance evaluation results for this machine will be presented. The project’s is focused on developing new metrology tools and methods for meso-scale machine tools with small work volumes. This prototype machine is one of three meso-scale machine tools under development within the Machine Tool Metrology Group at the National Institute of Standards and Technology (NIST). Machine Design and Configuration The machine tool implementation described in this paper is that of a prototype three axis meso-scale mill configured for rotary milling applications (e.g. production of camera zoom lens bodies). This machine is a partial realization of a five axis machine design [5]. The prototype machine is designed for a 25 mm cubed work volume. The workpiece is supported by a THK * ballscrew-spline that is driven by a DC brushless motor coupled by a cable- capstan drive transmission. This configuration provides 60 mm of linear motion and 340 degrees of rotary motion of the workpiece. In addition, the prototype machine includes a high speed spindle which has 10 mm of linear motion along the spindle axis of rotation. A voice coil actuator with a linear encoder is used to close the servo loop that positions the end mill tool mounted in the spindle. The spindle is orthogonal to the ballscrew-spline shaft (and its linear motion) as shown in Figure 1 (a) and (b). The prototype machine is unique in the use of a ballscrew-spline to support and position a workpiece in place of slideways used on traditional machine tools. For the meso-mill application, the ballscrew-spline shaft resembles a large lead ballscrew shaft with additional linear ball grooves ground along the length of the shaft. Located on the shaft are two ball nuts (one ballscrew nut and one ball-spline nut) whose outside flanges are bolted to opposite ends of a precision ground rectangular cast iron fixture. As the ball screw nut is rotated, with the ball spline nut fixed, the shaft translates linearly. As the ball-spline nut is rotated, with the ballscrew nut fixed, the shaft both rotates and translates. By coordinating the rotary motions of both nuts, it is possible to obtain only rotary motion or only pure linear motion of the shaft. This coordination is achieved through the use of the coordinate system capabilities on the motion control board. This enables the user to program the machine using traditional linear and rotary program statements. The ball nut is fixed within the mounting flange through ball bearings captured in two opposing angular contact ball bearing raceways. The outside diameter of the ball nut has opposing angular contact bearing raceways machined on itself and the inside diameter of the mounting flange has corresponding bearing raceways machined in its internal diameter. In order to drive the nuts, a 305 mm machined drum is bolted to each of the ball nut end faces. Two * Commercial equipment, instruments, or materials are identified in this report in order to specify adequately certain procedures. In no case does such identification imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the material or equipment identified is necessarily the best available for the purpose.