A proper answer requires a detailed look at the overall EDM operation. The practice of using a standard electrode reduction amount is very common, but it might not yield the best Accuracy or Machining Speed results.

Pros of using a common electrode undersize:

• Using a common or standard electrode reduction amount for all electrodes will streamline and simplify the programming of electrodes. In many shops, the electrodes are machined by milling, and the mill programmer may have little knowledge of EDM.
• Applying the same electrode reduction to all electrodes prevents EDM setup and tracking confusion. If all electrodes have the same reduction amount, there is no need to mark or measure every electrode during EDM setup.
• Applying the same electrode reduction to all electrodes allows greater EDM process flexibility, as the electrodes can be shuffled around and reused as roughers and finishers when needing to produce multiple cavities of the same contour (for example, cavity #1 finish electrode becomes cavity #2 roughing electrode).

Cons of using a common electrode undersize:

• Using a standard electrode reduction amount can rob a shop of valuable machining time, as too small an electrode reduction will force the EDM operator to use a lower-power discharge setting to maintain proper size. This results in slower machining speeds and increased electrode wear.
• Using different electrode reduction amounts between the roughing and finishing electrodes can improve machining speeds (faster roughing and less orbiting on finishing).
• Using different electrode reduction amounts between the roughing and finishing electrodes can improve form accuracy, as the finishing electrode is machined closer to the final net shape of the desired cavity.
• It is important to establish a reliable identification system when manufacturing electrodes with different reduction amounts, such as a marking or color code system on the electrode holder, for roughing and finishing.

Intelligent review on electrode preparation:

• It is paramount that the EDM operator and electrode milling programmer communicate and discuss a plan for electrode reduction for each job.
• Through proper review and planning, a shop can gain significant efficiencies in its EDM operations by applying the optimal electrode reduction amount that will produce the fastest machining speeds (roughing speed will see the biggest benefits).
• The use of different electrode reduction amounts can be strategically deployed on critical part details that require tighter tolerances.
• For more open tolerance details, a standard electrode reduction size can be established.