Production Machining

OCT 2017

Production Machining - Your access to the precision machining industrial buyer.

Issue link:

Contents of this Issue


Page 28 of 59

squares method of calculation, which traditionally has a difficult time processing a circle algorithm if both point and form data sets are insufficient. When taking a closer look at how the number of points affect radius measurement, users will see the circle algorithm is highly dependent on the points encom- passing a large arc segment (more than 45 degrees). Measurement of a short radial segment can cause errors in the size and location issues; repeatability of the form is a key contributor as well. Here are some rules of thumb for measuring radii: • Measure a large arc segment. • Use more than the minimum number of measure- ment points (more than three). Doing so will provide a roundness (form) result. is result is critical to determine if the radius measurement is repeatable and accurate. e larger the form error, the more likely the feature measurement is affected by variability of point data. • To improve radius measurement, increase the number of points, examine the points along the radius measurements for overlapping or expand the measuring of the arc area. Roundness e roundness measurement on a cylindrical part is common with a touch probe measuring system, yet it is a misconception that this is a best practice. While many quality professionals feel that this is the best method for in-process inspection, there are a few rules to consider before using tactile probing methods to guarantee round- ness. Many turned parts have a roundness callout with tight tolerance parameters. Here are considerations for tactile touch probing when evaluating roundness: • Is the roundness tolerance specification more than a quarter of the stated accuracy of the touch probe device/measurement system? If so, system measurement error could account for a large portion of the tolerance zone. is is not recom- mended, as uncertainty error influences may make the system incapable of obtaining the roundness. • Touch probes have a profound effect on round- ness. Mechanical/electrical probes can have an error of many microns and create a triangular shape known as probe lobing. Strain gage touch- trigger probes work in a different method and have a reduced probe lobe effect, which renders them a better choice for improving roundness measurements. :: When measuring a variety of parts with varying tolerances and features, consider a system that incorporates both contact and noncontact measurement methods. :: The size of stylus tip plays an important factor in measurement with a touch probe. The stylus radius should not exceed the radius of the feature to be measured. A spherical stylus is the most common and cost-effective choice. INSPECTION/MEASUREMENT :: 27

Articles in this issue

Links on this page

Archives of this issue

view archives of Production Machining - OCT 2017