Microhardness tester

Abstract

A microhardness tester comprises a turret capable of holding a plurality of load rod assemblies such that, when the optical objective elements mounted on the turret have been properly aligned with respect to the indenter of one load rod assembly desired to impinge upon a specimen to test for microhardness and it subsequently becomes desirable to use a second load rod assembly to change scales for the testing, it is only necessary to properly align the indenter of the second load rod assembly and not the objective elements with the test specimen. The load rod assembly of the microhardness tester free falls in its testing mode, and a spring is provided for retaining the load rod in a home position spaced away from the test specimen. Thus, the load weights applied to the load rod as carried to the test specimen are not affected by spring load tolerances such that weight calibration can be completed during the weight manufacturing process. Likewise, the weight stack constituting the additional load is guided on a vertical shaft impinging on the load rod so as to provide for actual weights without the need for calibrating spring gradients. The load rod assembly can also be removed from a tester without the necessity of internal disconnection. A threaded anti-rotation collar provides for easy adjustment of the gap between the load rod assembly indenter and the test specimen. The microhardness tester also comprises an elevating unit having a sprocket arrangement providing a rapid focus feature for moving a test specimen into the desired fine focus in minimal time. Still further, a standard dwell time is provided for the tester, with such dwell time factory preset.