Sinker EDM vs. CNC Milling: Which One Should You Choose?
Key differences between sinker EDM and CNC milling: materials, geometry, speed and cost. A technical guide for manufacturing engineers.
Sinker EDM or CNC Milling? It Depends on the Part
When a part has deep cavities, sharp internal corners or is made of hardened steel, choosing the right process sets the cost, lead time and final quality. CNC milling and sinker EDM do not compete: each solves different problems, and many projects use both.
What Is CNC Milling?
CNC milling removes material with a rotating cutting tool while the machine moves along several axes following a CAM program. It is the most versatile process for prismatic parts, plates, blocks, brackets and complex profiles in aluminum, steels, stainless steel and engineering plastics.
What Is Sinker EDM?
Sinker EDM uses an electrode, usually graphite or copper, shaped like the form to be produced. Thousands of controlled electrical sparks between the electrode and the part, both submerged in dielectric fluid, erode the metal with no physical contact and no cutting forces. It works on any conductive material, regardless of hardness.
Key Differences Between EDM and CNC Milling
Material hardness: EDM machines hardened steels and carbide as easily as soft steel; milling loses efficiency and wears tools in very hard materials.
Geometry: EDM produces sharp internal corners, narrow slots and deep cavities; in milling, the minimum internal radius depends on the tool diameter.
Speed: CNC milling removes volume much faster, so it is the natural choice for roughing.
Forces on the part: EDM applies no cutting pressure, ideal for thin walls and delicate details.
Cost: milling is usually cheaper; EDM adds the design and machining of the electrode.
When Should You Use EDM?
Mold cavities with fine details, ribs or textures.
90° internal corners a cutter cannot reach.
Parts already hardened that need modifications or repairs.
Deep, narrow forms where a long tool would vibrate or break.
When Should You Use CNC Milling?
Prismatic parts, plates, bases, brackets and housings.
Parts in aluminum, unhardened steel, stainless steel or technical plastics.
Prototypes and short runs where lead time is the priority.
When the geometry allows internal radii and there is a lot of material to remove.
The Best of Both: Combining Processes
In molds, dies and tooling, it is common to rough with CNC milling, heat treat, and finish with EDM the details the cutter cannot reach. Combining processes shortens total lead time and keeps precision in the critical areas.
Not Sure Which Process Your Part Needs?
At Precision Meteoro we have more than 25 years of experience in precision machining, with CNC milling, turning and sinker EDM under one roof in Desamparados, San José, serving manufacturers and free trade zone companies. We review your drawing or sample and recommend the most efficient route, including mold making.
Have a part in mind? Send us your drawing and get a technical review and quote.
