Technical Guide4 min read

Blade Ejection for Narrow Ribs: Minimum Width Guidelines

Key Takeaway: Minimum blade width for reliable ejection: 1.2mm. Below this, the blade becomes too fragile for repeated ejection cycles. For ribs narrower than 1.2mm, use round ejector pins with diameter = rib width.

Minimum Width by Application

Rib Width	Blade Width	Max Blade Length	Notes
3.0mm+	2.8mm	200mm	Standard application, M2 or H13
2.0–3.0mm	1.8mm	150mm	Moderate — use H13 for toughness
1.2–2.0mm	1.0–1.8mm	100mm	Limit case — guide bushing required
<1.2mm	N/A	N/A	Too narrow for blade — use round pin

Force Distribution Analysis

The advantage of blade ejection over round pin ejection for ribs: force is distributed along the full rib length, reducing peak stress by 60–80%. This prevents the rib from cracking or deforming during ejection — especially critical for brittle resins (PS, SAN, PMMA).

Frequently Asked Questions

Can I use a blade wider than the rib?+

No — the blade must be narrower than the rib (by 0.2mm) to fit inside the rib cavity. A blade wider than the rib would interfere with the cavity walls and cause mold damage.

What about ribs with draft angle?+

The blade tip width should match the rib width at the narrowest point (tip of the rib). The blade cross-section is uniform — it does not taper with the rib draft. The clearance between blade and rib wall increases toward the base due to the draft angle.