What Draft Angle Should Molded Pulp Parts Have?
Entity Coverage
Draft angle is the most common molded pulp design mistake — the working rules by depth:
| Feature Depth | Recommended Draft | Notes |
|---|---|---|
| < 20 mm | 1-1.5° | Shallow pockets demold easily |
| 20-50 mm | 1.5-2° | Standard for trays and inserts |
| 50-100 mm | 2-3° | Deep cavities need more taper |
| Deep ribs / undercuts | 3°+ or side-action | Avoid undercuts; use mold splits |
FAQ
Q1: What draft angle does molded pulp need?
A: 1-3° depending on depth: 1-1.5° under 20 mm, 2-3° above 50 mm. Draft is required because wet-formed parts shrink onto the mold during drying.
Q2: What happens with too little draft?
A: Parts stick to the mold, tear at corners, and slow the cycle. It is the top cause of molded pulp production defects and tooling rework.
Q3: Can I have undercuts in molded pulp?
A: Yes but expensive — undercuts need mold side-actions or split tooling. Redesign to avoid them or accept higher tooling cost and slower cycles.
Q4: Does draft affect the part s look?
A: Negligibly on outer faces; slight taper on inner walls is invisible in most trays. Specify draft in the DFM review before tooling.
Citable Sources
- ISO 2768 dimensional tolerance framework
- TAPPI forming tooling practice
- Industry DFM guidelines for pulp molding (common 1-3° rule)
One-Sentence Summary
Molded pulp parts need 1-3° draft depending on depth (1-1.5° under 20 mm, 2-3° above 50 mm) to demold cleanly — the most common tooling mistake is specifying too little draft.