Wire EDM vs. Sinker EDM
The most common question buyers ask. The answer is almost always straightforward once you understand what each process can and can't do.
Capability Comparison
| Factor | Wire EDM | Sinker EDM |
|---|---|---|
| Feature Type | Through-cuts and profiles | Cavities, blind holes, 3D shapes |
| Best Tolerance | ±0.0001" | ±0.0002" |
| Best Surface Finish | Ra 8 μin | Ra 8 μin (with orbiting) |
| Inside Corners | Wire radius (0.004"–0.006") | Electrode radius (very small) |
| Setup Cost | Lower (no electrode to make) | Higher (electrode fabrication) |
| Per-Part Cost at Volume | Linear with quantity | Decreasing (electrode amortized) |
| Unattended Operation | Excellent — lights-out capable | Good with tool changer |
| Typical Applications | Die sections, punches, gears, splines, extrusion dies | Mold cavities, forging dies, blind ribs, textures |
When to Use Wire EDM
Your feature is a through-profile — it goes all the way through the workpiece. Die openings, gear teeth, internal splines, extrusion die openings, stripper plate holes. If you can imagine pushing the shape through the block like a cookie cutter, wire EDM is your process.
When to Use Sinker EDM
Your feature is a blind cavity — it doesn't go through. Injection mold cavities, forging die impressions, blind keyways, rib details, textured surfaces. If the feature has a bottom, sinker is your process.
When You Need Both
Many tool and die jobs use both processes on the same workpiece. Wire EDM cuts the through-profiles, then sinker EDM adds the blind cavities and detail features. A shop that runs both processes in-house eliminates a handoff and holds tighter overall tolerances because there's no re-fixturing between shops.
If your project needs both wire and sinker EDM, find one shop that does both. Every time a part ships from one shop to another for additional operations, you lose time, risk damage, and accumulate tolerance stack-up from re-fixturing. A single shop running both processes controls the entire workflow and takes ownership of the final result. The best shops run both processes under one roof for exactly this reason.