Design for EDM

Wire EDM Design Principles

Wire EDM cuts profiles, not cavities. Think of it as a bandsaw that can cut any shape, in any material, to extreme precision — but it has to enter from an edge or a pre-drilled start hole, and it cuts all the way through the workpiece.

Inside corners are free. One of EDM's greatest advantages over milling. Wire EDM cuts sharp inside corners with a radius equal to wire diameter — typically 0.004"–0.006". On a mill, inside corner radius equals the cutter radius, so you're limited to 0.0625" or larger. If your design has sharp internal corners, EDM is likely your process.

Taper is possible but adds cost. Most machines cut tapered profiles up to ±30° by offsetting upper and lower wire guides independently. Taper cutting runs significantly slower than straight cuts. If you can design with zero taper, you save money.

Start holes matter. Every closed internal profile requires a start hole — typically 0.020"–0.040" diameter, drilled conventionally or by small-hole EDM. Fifteen internal features means fifteen start holes means fifteen positioning cycles. Consolidate internal features or design with edge access where possible.

Workpiece thickness affects everything. Thicker material = slower cutting, more wire consumed, higher risk of wire breakage. A 6" tall part costs significantly more per inch of profile than a 1" tall part. If tolerances allow, consider splitting tall parts into thinner sections cut separately.

Sinker EDM Design Principles

Electrode complexity drives cost. Someone has to machine the electrode first — usually by milling graphite or copper. Complex electrode geometry means complex (expensive) electrode machining. Simple cavity shapes with generous radii are cheaper.

Draft angles help but aren't required. Unlike injection molding, sinker EDM doesn't need draft for electrode retraction. But adding 0.5° per side improves flushing, reduces electrode wear, and improves surface finish.

Depth-to-width ratio matters. Deep, narrow cavities are hard to flush — dielectric can't circulate effectively. Ratios above 4:1 start getting problematic. Above 8:1, expect significant cost increases and longer lead times.

Rib and detail features need electrode changes. Each distinct depth or feature typically requires a separate electrode or adjustment. A cavity with three depth levels might need three electrodes. Design with the fewest distinct depth levels practical.