Introduction
If you’re designing parts for injection molding, you’ve likely heard of draft angles. These are small tapers added to vertical walls of a part to help it release from the mold.
But what if your part is really small—say, 6 mm or less? Do the same rules still apply?
This post explains how draft angles work for tiny parts. You’ll see why they matter, when they can be adjusted, and what to watch out for—based on real industry input.
The Basics: Why Draft Angles Matter
What Is a Draft Angle?
A draft angle is a slight slope—usually starting at 1° per side—built into the vertical walls of a part.
Why it’s important:
Plastic parts shrink as they cool. Without draft, the part may grip the mold tightly. This can lead to damage, delays, or tool wear during ejection.
Risks of Skipping Draft
Too little draft can lead to:
- Drag marks or scuffing
- Parts getting stuck in the mold
- Broken features during ejection
- Wear on the mold
- Longer cycle times
The 1-Degree Rule
A common rule is to start with at least 1° of draft per side. This helps avoid ejection issues and keeps production smooth.
Tiny Parts, Special Considerations
Why Small Parts Raise Questions
If your part is tiny—under 6 mm—should you still use a full degree of draft?
In past projects, a few clients have asked the same question. One of them said, “For parts this small… do I really need draft?” The concern makes sense—tight spaces leave very little room for angled features.
What Matters Most
When deciding on draft for small parts, think about:
- Material type – Some plastics, like polystyrene (PS), shrink less and may not need much draft.
- Mold surface finish – A polished core can reduce sticking, allowing for less draft.
- Part shape – Simple shapes release easier. Sharp corners or deep ribs may need more draft.
- Tooling and ejection system – Precise molds and strong ejectors matter more when space is tight.
Is Less Than 1° Possible?
Yes, in certain cases. We’ve successfully achieved draft angles as low as 0.25° for our clients, especially when:
- The part only contacts one side of the mold
- The mold has a smooth, polished finish
- Ejection is supported by features like ejector pins or sleeves
- The geometry is simple
At an industry event where we shared our success cases, a fellow professional commented, “0.25° can work, but everything else has to be just right.”
Why It’s Still Safer to Stick to Standards
Trying lower draft angles can work, but it increases risk. You may see:
- More rejects
- Tool damage
- Extra tooling costs
Using 1° per side is more forgiving. It works with more materials and surface finishes, and helps make production reliable and repeatable.
Best Practices for Small Part Design
To design tiny molded parts successfully:
- Use draft whenever possible
- Start with 1°, but go lower only when supported by mold finish, part shape, and material
- Polish mold surfaces to help with part release
- Choose materials carefully, based on shrink and friction
- Talk with your mold maker early—their input is key
Conclusion
Draft angles matter, even for small parts. The general rule—1° per side—is a solid starting point.
Yes, lower angles like 0.25° can work on very small parts, but only under the right conditions. You’ll need the right material, tooling, surface finish, and expert guidance.
When in doubt, follow standard practices. They’re standard for a reason.
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