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68 MMS April 2017 mmsonline.com CNC TECH TALK Columnist adjustment affects them all. Pick and identify the most critical of them (per adjustment) for measur- ing, and specify it in the process documentation. 4. Specify the gage needed for each mea- surement. For variable gages like micrometers and calipers, it may be enough to simply specify the gage name (a 0-1-inch micrometer, for instance). For special fixed gages, be sure to also specify the gage number. If special or unusual gaging tech- niques are required, be sure to document them. Depending on the skill level of your workers, it can help to include additional measuring instructions, perhaps incorporating a photograph or video. 5. Specify measurement frequency. Be sure to prescribe how often inspections must be done, usually in terms of number of completed workpieces. 6. Trend information. Cer tain workpiece attributes, and especially those machined by single-point cutting tools on turning centers, will grow or shrink during the cutting tool's life (due to tool wear). With trending workpiece attributes, be sure to specify the action point. It should take into consideration the measurement frequency so as not to allow workpieces to trend out of tolerance between measurements. Say, for example, you specify the action point at 20 percent of the over- all tolerance. When a workpiece attribute having an overall tolerance of 0.004 inch grows or shrinks within 0.0008 inch of a tolerance limit, the opera- tor is expected to make a sizing adjustment. 7. Specify the adjustment method. Be sure to tie each workpiece attribute requiring an adjust- ment to the manner by which the adjustment must be made. If a cutting tool must be physically adjusted (like a boring bar used on a machining center), be sure to specify as much. If a CNC offset adjustment is required, specify the offset number and type. For example, if a turned diameter attri- bute is being machined by a finish turning tool using offset number 3, specify that it is the X-wear register for of fset number 3 that provides the adjustment. This will keep workers from having to know/remember which cutting tool machines each workpiece attribute.