Rectangular Shank Ejector Blades

Rectangular shank provides two critical advantages: (1) Zero-rotation guarantee — the rectangular profile physically cannot rotate in a matching rectangular bore, eliminating the need for set screws, anti-rotation pins, or other secondary locking mechanisms. This is essential for blades ejecting features with specific orientation requirements (e.g., asymmetric ribs, text embossing). (2) Higher lateral load capacity — the rectangular shank distributes lateral forces across flat contact surfaces rather than point/line contact, increasing resistance to side-loading by 30–50% compared to round-shank blades. The tradeoff is higher plate machining cost (rectangular bore requires EDM or wire-cut).

Yes — this is the primary reason for choosing rectangular shank. The rectangular bore-to-shank interface provides a form-fit anti-rotation lock with zero backlash. This is mechanically superior to round-shank anti-rotation methods (set screws, keyways, D-flats) which all have some clearance and can loosen over time. For applications where blade orientation must be maintained within ±0.5° over millions of cycles, rectangular shank is the only reliable solution. The bore-shank clearance on rectangular profiles is typically 0.01–0.02mm per side (H7/h6 fit), which prevents rotation while allowing smooth axial sliding during the ejection stroke.

Rectangular shank blades require a matching rectangular bore in the ejector plate, typically produced by wire-EDM or sinker-EDM. The bore must have: (1) H7 tolerance on width and thickness (e.g., +0.012/0 for a 4mm dimension), (2) corner radii matching the shank corner radii (typically R0.1–R0.3mm — sharp internal corners are not achievable with EDM), (3) surface finish Ra ≤ 1.6μm on all four walls for smooth sliding. EDM machining time is approximately 30–45 minutes per bore, compared to 5 minutes for a round bore. This higher preparation cost is the main tradeoff — justified only when anti-rotation reliability is mission-critical.