Ejector Pin Tip Shapes: Flat, Radius, Chamfer — Application Guide
Tip Processing Types Compared
| Tip Type | Processing | Best Application | Lead Time Impact |
|---|---|---|---|
| As-Ground (no processing) | None — factory finish Ra 1.6μm | Non-cosmetic surfaces, structural parts | Standard (1–3 days) |
| Flat Grind | 0.05mm removed from tip face | General cosmetic surfaces, eliminating ring marks | +2–3 days |
| Radius | R0.5–R2.0 convex profile | Contoured part surfaces, preventing edge-catch | +2–3 days |
| Chamfer | C0.2–C0.5 at 45° | Guided bore entry, simplifying mold assembly | +2–3 days |
| Z-Groove | Cross-groove 0.02–0.05mm deep | Gas venting at pin-bore interface | +3–5 days |
When to Choose Each Type
Flat Grind — The Universal Upgrade
Standard ejector pins leave a slight recessed ring mark on the part surface where the pin-bore clearance gap creates a step. Flat grinding removes this step by machining 0.05mm from the tip, creating a perfectly flush surface. Cost premium: approximately $0.50 per pin. According to Moldmaking Technology, flat-ground tips reduce visible ejection marks by 80% compared to as-ground tips.
Radius — For Contoured Surfaces
When the part surface at the ejection point is curved (e.g., inside of a cylindrical housing), a flat tip creates edge-catch during ejection. A radius tip (R0.5–R2.0) matches the part curvature, distributing ejection force smoothly. Select the radius to match the part surface curvature within ±20%.
Z-Groove — Hidden Gas Venting
Z-groove tips provide micro-venting (0.02–0.05mm deep cross-groove) at the pin-bore interface without the complexity of full gas release pins. Suitable for mild gas trapping — not a replacement for dedicated gas release ejector pins in severe venting applications.