PRECISION MOLDMAKING & SINKER EDM
Die Sinking EDM Electrode & Spark Gap Vector Guide
Die sinking (ram/cavity) electrical discharge machining (EDM) uses shaped graphite or copper electrodes immersed in dielectric hydrocarbon oil to burn complex, intricate 3D cavities into hardened tool steels (H13, S7, D2, 60+ HRC) that cannot be machined by conventional rotary endmills. Because electrical sparks jump across a microscopic spark gap ($0.02 - 0.25\text{mm}$) before the electrode makes physical contact, the physical electrode must be manufactured undersized in CAD/CAM by the exact spark overcut plus the planetary CNC orbit radius.
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1. Electrode Spark Overcut & Orbiting Math
Total per-side dimensional reduction ($\Delta_{ ext{side}}$) required in the electrode 3D CAD model:
2. Graphite Grade Selection for CNC Electrode Milling
| Graphite Grade | Average Grain Size | Target Application | Corner Wear Resistance |
|---|---|---|---|
| Ultra-Fine (POCO EDM-3 / TTK-4) | $< 5\,\mu ext{m}$ | Complex injection mold cavities, textured logo details | High resistance, sharp edge retention |
| Micro-Fine (EDM-1 / TTK-50) | $10 - 15\,\mu ext{m}$ | General roughing and semi-finishing mold dies | Moderate corner radius rounding |
| Tellurium Copper | Solid alloy | Stamping dies requiring mirror polish without orbiting | Zero chip dusting, high thermal stability |
3. Vector Prepress Rules for Sinker EDM
- Draft Angles: Always include minimum $1.0^\circ - 2.5^\circ$ draft on vertical cavity ribs in the vector model to facilitate molded plastic part ejection and dielectric flushing.
- Flushing Holes: Incorporate internal $ arnothing 1.0 - 2.0\text{mm}$ through-hole vectors for pressure flushing channels to prevent carbon buildup and localized arcing.
Convert Scans to Precision Tooling DXF
Upload legacy die drawings, stamp logos, or mold core profiles. SpotItLive produces high-accuracy vector DXF/SVG files calibrated for CNC electrode milling.
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