Jan 23 2008
The Talyrond 395 is designed specifically for the measurement of ultra high precision parts such as fuel injectors and Hard Disk Drive bearings. Automated software routines for both measurement and analysis make this system ideal for high volume production applications. The low system noise and high precision movement axes, combined with a dual purpose high resolution gauge have enabled Taylor Hobson to produce the first roundness system with roundness, linear and circumferential roughness.
Roundness Measurement
The Talyrond 395 roundness instrument is similar to the machines that produce the components in the first place. For example, a simple lathe has a rotating spindle, one slide way moving with the axis of the spindle and another slide way for moving across the axis of the spindle. The Talyrond 395 is similarly equipped with a high-precision spindle, a slide way (column) for movement along the spindle axis and another slide way (radial arm) for movement toward or through the spindle axis.
An obvious fundamental difference is that the lathe is cutting the part and the roundness instrument is measuring that part. The forces involved are considerably different, as are the axis speeds. Although the stylus of the measuring device is often following the same path as the cutting tool on the lathe, the Talyrond instrument must have greater positional control of the axes and a much higher level of accuracy in the reference data.
Simply stated the spindle-based Talyrond 395 utilises the best method for measuring rotationally symmetric components that are produced on a spindle based machine tool. The manufacturing process is duplicated, albeit with a higher degree of accuracy. Traditionally, roundness instruments have detected errors of form or geometry, but there is a strong case for doing more, for detecting and evaluating cutting tool effects such as surface finish.
Incorporating Surface Finish Measurement
Since errors of roundness and surface finish occur simultaneously at the manufacturing stage, it seems logical that an inspection instrument should measure roughness and roundness at the same time. As manufacturers have one engineering drawing and one machine tool to produce the component, they would ideally have one instrument to check the finished part.
In the past, this has been difficult, if not impossible. Stylus force, measurement speed, system noise, data point resolution and other factors made the roundness measurement incompatible with the surface finish measurement. However, recent developments have had a direct effect on surface and roundness tolerances. Taylor Hobson have responded with a new wave of higher-accuracy, lower noise roundness systems. These advanced systems not only measure roundness, form and geometry, but surface finish as well.
Roughness characteristics are typically measured either along the axis of the component or around the axis of the component, depending on how the part is produced and how it has been engineered to function. The Talyrond 395 can be used to measure a component circumferentially using a diamond stylus and 72,000 radial data points (0.005º data point spacing) or alternatively in the axial direction of a component with 200,000 data points and a resolution akin to laboratory equipment.
Both linear and circumferential surface roughness have their merits. Basically a defect or scratch in a radial direction cannot be detected with a measurement in the radial direction and likewise a scratch or defect in the axial direction of the component cannot be detected with a trace made in the same axial direction. This mistake is often made on sealing surfaces such as on fuel injection seals whereby a scratch in the axial direction may cause leakage but will not be detected by conventional axial traces; a corrugated surface would look flat if measured along the corrugation.
With automatic centering and levelling of the component the TR395 assures flawless alignment regardless of measurement direction. While 2-D profile information is often sufficient for problem solving, it may be beneficial to create a 3-D map of the surface. This is done by performing a series of straightness traces that are then combined into a 3-D dataset.
Together at Last
Obviously, not all roundness instruments are capable of combining surface finish and roundness measurements. Precision glass scales and precise motion control in all axes, high data density, and low instrument noise are mandatory design elements. Equally important, the dual inspection functions must be seamlessly integrated into a single software package. For true convenience, the gauge head should be dual purpose and ready to use with both diamond- and ball-tipped styli. With all of these elements incorporated properly, the
dual-purpose Talyrond 395 exceeds the capability of many dedicated roughness checkers and offers improved repeatability and reliability. With one instrument and one operator,
manufacturers can inspect components as they are engineered and produced.