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mmsonline.com April 2017 MMS 77 FEATURE a xes can then be adjusted so that the wire is normal to the part surface. This process is slower and less precise than automatic touch-trigger probing, but it offers a less-expensive alternative using a common shop measurement device. • Sinker EDM. As with wire EDM, a sinker machine's electrode can be used as the par t probe. However, it similarly isn't as accurate as more advanced probing options. For example, graphite electrodes could have debris on their sur face s and copper electrode s could have bur r s f rom milling. B oth situ ations c a n limit probing accuracy. That's why it is becoming more common to use a tooling ball system for probing. These sys- tems use two rigid tooling balls, one mounted in the machine's spindle (via a 3R, Erowa, Hirschmann or similar interface) and the other that installs on the machine's table using a simple magnetic base. A low voltage applied to the spindle ball (approx- imately 5 volts) is used to electrically touch-off points on a part. For each new job, a correlation between the position of the center of the spindle ball and the center of the table ball (therefore electrode and part) first must be established. The position of the table ball on the table isn't important. In fact, it often must be moved depending on the size or geometry of the new part to be machined. The spindle ball creates an offset to the part by touching off on the part to establish its actual location on the table. Makino's Hyper I control offers seven canned cycles for this, the four most common of which are plate center, hole center, corner find and measure angle functions. The table ball is used to determine the true electrode size, loc ation a nd of f sets. Common c a nne d cycles for this include plate centering, which is a four-sided pick-up function; hole centering; and three-point centering on the inner or outer diameter of a cylindrical electrode. Users have the option of setting up all electrodes prior to machining a job to establish offsets for each, or the probing routines can be incorporated into the machining program cycle. With this latter method, the machine automatically performs a probing routine to determine the electrode center location as each new electrode is loaded into the machine during program operation. In fact, Mr. Pfluger says Makino offers offline programming software for its sinker EDM equip- ment called EDcam that enables offline probing routine programming using 3D CAD data for the electrodes and workpiece as an alternative to traditional programing at the machine. The soft- ware also automatically calculates the discharge area based on the CAD models to determine the proper EDM power settings. The company is releasing a version of EDcam in April that offers an interface that's similar to the Hyper I control. That way, the inter face for machine setup and A rigid spindle ball is commonly used on sinker EDM units to determine part location and offsets. Similarly, a table ball can quickly determine electrode offsets.