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You’ve designed a mold cavity with a perfectly square internal corner. Your CNC mill sighs — because a round cutter can only ever leave a round corner. The smaller the tool, the closer you get, but you’ll never hit a true sharp corner. That’s the dirty secret of subtractive machining.
Wire EDM doesn’t have that problem. Because the “tool” is a thin wire that erodes rather than cuts, it can hold tolerances around ±0.001 mm and carve internal corners a mill can only dream about. Let’s look at why, and what it means for your next part.
What Tolerance Can Wire EDM Actually Hold?
- ±0.001 mm as standard. That’s roughly one-fiftieth of a human hair — comfortable production territory for most wire EDM shops.
- Down to ±0.0001 inch on precision jobs. Multi-pass “skim cuts” (a rough pass followed by several finishing passes) push accuracy even further, to about 0.0025 mm.
- Internal corner radius near zero. Where a mill is stuck with its cutter radius, a wire can approach a true 0° corner — commonly down to about 0.05 mm, with some shops quoting internal corner radii as small as R.008 inch.
- Repeatability, part to part. Because there’s no tool wear, the 5,000th part matches the first.
Why Sharp Internal Corners Are a Big Deal
A rounded corner isn’t just a cosmetic miss. In real parts it causes real headaches:
- Mold & die cavities — a fillet traps material and ruins the molded part’s edge.
- Extrusion and punch profiles — the corner radius becomes the product’s corner radius, whether you want it or not.
- Snap-fit and locating features — a looser corner means a looser, rattly assembly.
Wire EDM lets you put the corner exactly where your drawing says — no “as-milled” compromise.
Wire EDM vs Milling — The Precision Table
| Feature | CNC Milling | Wire EDM |
|---|---|---|
| Contact method | Physical cutting | Electrical erosion (no touch) |
| Material limit | Most materials | Conductive only |
| Typical precision | High | Ultra-high (±0.001 mm) |
| Internal corners | Rounded (cutter radius) | Sharp (0° radius possible) |
| Tool wear | Yes | None (constant wire feed) |
| Surface finish | May need finishing | Often smooth & burr-free |
Design Tips for Tight-Tolerance Wire EDM
- Leave stock for skim passes. Rough first, finish last — don’t expect one pass to do both.
- Specify your corner radius realistically. We can get close to zero, but telling us the target helps us pick the wire and passes.
- Avoid super-thin unsupported ribs. Zero force helps, but a 0.1 mm rib between two deep slots can still be fragile to handle — design for it.
The Honest Limitations
- Slower than milling for roughing. Wire EDM wins on finish and detail, not on material removal rate.
- Conductive materials only. No plastic, wood, or glass.
- Setup time. Programming complex contours takes care — but it pays off in the part.
FAQ
How tight a tolerance can wire EDM hold?
Typical production tolerance is around ±0.001 mm, and multi-pass skim cuts on precision jobs can reach roughly ±0.0001 inch (about 0.0025 mm).What’s the smallest internal corner radius wire EDM can cut?Is wire EDM more accurate than CNC milling?
How tight a tolerance can wire EDM hold?
Precision hardware & non-standard manufacturing specialists based in Dongcheng, Dongguan, China. Wire EDM, CNC machining, forging & die casting, and sheet metal — built to your drawing, not a catalog.
What’s the smallest internal corner radius wire EDM can cut?
Because the wire has no rotating cutter radius, internal corners can approach a true sharp corner — commonly down to about 0.05 mm, with some shops quoting internal corner radii as small as R.008 inch.
Is wire EDM more accurate than CNC milling?
For fine features and sharp internal corners, yes. Milling is limited by cutter radius and tool pressure; wire EDM removes material without contact, so it holds tighter tolerances on delicate and hard-to-reach geometry.
So, Is Tight-Tolerance Wire EDM Right for Your Project?
If your part lives or dies on its corner radius and its tenth-of-a-millimeter accuracy, wire EDM is the process. At Changye we hold ±0.005 mm as our standard wire EDM tolerance and push tighter on request — built to your drawing, not a catalog limit.
