In casting design, one feature is often overlooked—yet without it, production is impossible. Draft angle is the slight taper applied to vertical surfaces, allowing patterns to be removed from molds without damaging the sand. At Juize Machinery, we understand that proper draft design balances manufacturability against final geometry. As a Gold Verified Supplier on Alibaba, our castings reflect this practical knowledge.
What Is Draft Angle?
Draft is a gradual taper (typically 1–3 degrees per side) on surfaces parallel to the parting line. The pattern tapers inward toward the parting line, so it slides out of the sand without scraping or tearing the mold.
Why Draft Is Essential
Without draft:
Patterns cannot be withdrawn without damaging the mold cavity
Damaged molds produce misshapen castings with sand inclusions
Repairing molds adds time and cost
With proper draft:
Smooth pattern extraction, even on deep vertical surfaces
Clean mold cavities produce accurate castings
Faster production cycles
How Much Draft Is Needed?
Draft angle depends on several factors:
Casting Height: Taller surfaces need less angle per side (1° may suffice), but total taper on diameter increases with height.
Sand Type: Resin-bonded sand retains shape better than green sand, allowing slightly lower draft.
Pattern Material: Metal patterns withstand more extraction force than wood patterns, permitting lower draft.
Surface Finish Requirement: Higher finish demands cast-in as-cast surfaces may need slightly more draft to avoid drag marks.
Alloy: Low-draft designs are more feasible with high-fluidity alloys like gray iron or aluminum.
Typical Draft Guidelines
| Process | External Surfaces | Internal Surfaces (in cavities) |
| Green Sand | 1.5° – 3° | 3° – 10° |
| Resin Sand | 1° – 2° | 2° – 5° |
| Investment Casting | 0.5° – 1° | 1° – 2° |
| Die Casting | 0.5° – 2° | 2° – 5° |
Internal surfaces require more draft because the sand core must be withdrawn from the cavity.
Designing With Draft
Our engineering team advises on draft placement to minimize impact:
Add draft to non-critical surfaces where geometry must be maintained
Use parting line placement to hide draft on unseen faces
Consider alternative processes (investment casting or machining) for zero-draft features
Draft and Machining
If draft cannot be tolerated on a functional surface, we add machining stock. The as-cast surface includes draft; final machining removes the taper, leaving a straight wall.
