Wire EDM Sharp Corners: When Milling Can't Get There
Wire EDM sharp corners reach about 0.006" (0.15 mm) radius with standard wire, far tighter than an end mill. When EDM pays off, and when a fillet wins.
An end mill is round. Every inside corner it cuts has at least its radius, and no amount of programming changes that. Wire EDM sharp corners are the usual way around it.
How Do You Machine a Truly Sharp Inside Corner?
On a through profile in conductive metal, wire EDM gets much closer to sharp than a cutter can. In a blind pocket, ask first whether you really need sharp, because the answer is usually a small radius.
An r/Machinists user asked how to get a sharp inside corner where a boss meets a round diameter, on a 3-axis mill. The top reply suggested surfacing it with a nearly flat end mill with a .005 or .010" corner radius, and pointed out that even aerospace standards call "sharp" .000 to .005". Another described turning the part, then milling the tab and blending away the leftover cutter radius in .001" Z steps. One reply just said wire EDM. Another asked the better question: why does it need to be sharp at all?
How tight wire EDM sharp corners get
NORAMARK's wire EDM guide puts the minimum internal corner at the wire radius plus the spark gap. That's about 0.15 mm (0.006") with standard 0.25 mm wire. Thinner wire goes tighter but costs more.
It also lists the catches. Wire EDM only cuts through profiles, every internal profile needs a start hole, and non-conductive materials can't be cut at all. It's slow, too. NORAMARK says a 25 mm thick steel part roughs at a few millimeters a minute.
Hardness doesn't matter to the wire. NORAMARK says parts can be hardened first and cut finished, with no heat-treat distortion to correct afterwards.
When to skip it
Blind pockets are out, since the wire has to pass through. A milled radius is the usual answer there. Plastics like Delrin can't be EDM'd either.
Most of the time a fillet is the cheap answer. Size it a bit over a standard end mill, as our internal fillet radius post explains, and the part gets faster to make. Small cutters reaching deep into corners are where chatter on new end mills and stalls in tougher metals start showing up.
Where DigiForge fits
The CNC capability page lists a Sodick VN600Q, described as "wire EDM for hard metals and features milling cannot reach". It doesn't list sinker EDM. If a corner has to be sharp, mark it on the drawing and say why. For which materials and thicknesses suit the wire, ask us when you quote.
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