Modern Machine Shop

JAN 2017

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68 MMS January 2017 CNC TECH TALK Columnist path, and if the planned cutter size is used, the initial offset setting will be zero. CAM systems can generate either cutter center line path or work surface path; it is simply the programmer's choice. On the other hand, manual programmers writ- ing with G code usually find it more difficult to program the cutter's center line path and tend to program work surface path instead. Since the initial adjustment is easier when programming the center line path (zero, if the planned cutter size is used), this is our recommended method if a CAM system is used to create the CNC program. Sizing adjustments are done in the same manner regard- less of which programming method is chosen. Tool-length compensation offset specifi- cation (cutting tool length vs. distance from tooltip to Z-axis program zero surface). This decision is based on lot sizes, cycle times, how often the same cutting tools are used from job to job and the availability of support personnel. The more time there is during one job to get ready for the next job, the more important it is to use the cutting tool's length as the offset value. The tool length is the distance from the tooltip to the spindle nose, a positive value. This length can be measured either on the machine or offline, it will remain consistent from one job to the next, and it will even remain consistent among multiple machines. For these reasons, we recommend using the cutting tool's length as the tool-length compensation offset value. With this method, the Z-axis program zero assignment value, the work coordinate system offset Z register value, will be the distance from the spindle nose to the Z-axis program zero surface (a large, negative value). Even if there is limited preparation time and cutting tool lengths must be measured during setup, it is just as easy to measure a cutting tool's length on the machine as it is to measure the dis- tance from the tooltip to the Z-axis program zero surface. If cutting tools are often used from job to job, using the cutting tool length as the tool-length compensation offset value will save the duplicated effort required for measuring. DEBURR ANY CROSSHOLE

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