Touch probes for machine tools are amazingly flexible tools, offering a range of application possibilities that are often only limited by a user’s knowledge and imagination. The most common uses are for part and fixture setting, but increasingly due to enhanced designs and ever more powerful software they are being used to verify the dimensions of machined parts, before removal from the machine tool.
In a recent post, we mentioned the new ‘Ask the expert’ initiative from the US-based magazine Modern Machine Shop, where its readers can pose questions on-line to Renishaw’s US-based teams on a range of measurement and calibration issues. A recent question about the use of machine tool touch probes is quite common, so we thought it would make sense to share the response of Dave Bozich, our US machine tool business manager.
Q: I am interested in using our machining center’s Renishaw probe both for inspecting parts, as well as for crash prevention by locating bolts or clamps. Do you have any advice?
A: Using a probe for post process inspection is possible, but it’s a challenging issue. We generally suggest that customers keep their machines calibrated and properly aligned by using a laser interferometer, telescoping ballbar and other alignment equipment. We also suggest using strain gauge probes (such as Renishaw’s RMP600) vs. conventional kinematic probes. Strain gauge probes provide sub-micron repeatability. In addition, the use of a machine-resident artifact allows for correlation between the actual measurements taken from the part and the known dimensions of the artifact. PC-based data analysis software (Renishaw has OMV-Pro and CNC Reporter) may also be part of the solution.
Regarding using a probe for crash prevention, that is much simpler. You will first need to determine if you are using Renishaw macro software or something provided by the machine tool builder. Renishaw’s Inspection+ software provides a "Protected Positioning" cycle. This is a canned cycle used when positioning from feature to feature within a probing cycle. If the probe is inadvertently tripped as a result of interference with a clamp, machine motion is stopped and an error is raised. If you are not using this software, see if the machine tool builder’s software offers a similar routine.