Draft Angles: The Detail That Makes or Breaks a Molded Part
Supplier asking you to add draft? Draft is the taper that lets a molded or cast part release from the tool. How much you need, where engineers forget it, and what to do when a face can't have any.
If you've ever designed a part for molding or casting and the supplier came back asking you to “add draft,” here's what they meant and why ignoring it will wreck your part. Draft is the small taper on the vertical walls of a molded or cast part that lets it release from the tool. Leave it out and the part either won't come out, comes out scratched, or tears the tool up on the way. It's the single most common DFM miss we see from engineers who design like everything is machined.
Why draft is non-negotiable for tooled parts
Picture pulling a part out of a mold cavity. A perfectly vertical wall drags against the steel the entire way out — friction, scuffing, sticking. Taper that wall even a degree or two and the part breaks free of the steel the instant it starts moving, then slides out clean. No draft means ejector pins fighting a stuck part, drag marks down every wall, and a tool that wears prematurely. This applies to injection molding, die casting, and any process where the part is pulled from a cavity.
How much draft do you need?
It depends on depth, texture, and material, but the rules of thumb shops actually use:
| Surface | Typical draft |
|---|---|
| General molded walls | 1–2° (1° is a safe default) |
| Smooth / polished faces | 0.5–1° can work |
| Light texture | ~1.5° minimum |
| Heavy texture / deep grain | 3° or more — texture needs extra clearance |
| Deep ribs & bosses | More draft the deeper they go |
The deeper the wall, the more draft matters — a 1° taper barely changes a 5 mm wall but meaningfully tapers a 50 mm one. When in doubt, more draft is cheaper than a sticking part. Textured surfaces are the big gotcha: people add a grain for looks, forget to bump the draft, and the texture acts like sandpaper on ejection.
The mistakes that cost a tool revision
- Zero-draft walls. The classic. Looks fine in CAD, fails on the molding floor.
- Forgetting draft on ribs and bosses. Internal features need draft just like outer walls — and they're easy to overlook.
- Texture without extra draft. Add grain, add draft. Every time.
- Draft fighting your tolerances. A tapered wall isn't one dimension top-to-bottom. If a feature must hold a tight size over its full height, draft and tolerance collide — flag it early. This ties into wall thickness and overall moldability.
What if a face truly can't have draft?
Sometimes a sealing surface or a mating face genuinely must be straight. You have options, in rough order of cost: orient the part so that face is on the parting line (no draft needed), use a side-action in the tool (pricier mold), or mold it close and machine the critical face afterward — the same cast-then-machine hybrid we describe in casting vs machining. What you don't do is just delete the draft and hope.
The machining contrast
Here's why machinists-turned-designers trip on this: CNC parts don't need draft at all. There's no cavity to pull from — the tool just cuts straight walls. So a part designed for machining drops straight into a mold with zero draft and immediately fails. If you're moving a proven machined design to molding or casting for volume, a draft pass is the first thing to do, not the last.
Add a degree of draft to your vertical walls before you send the part and you'll save yourself a tool revision and a couple of weeks. Not sure where draft will bite on your specific geometry? Run it through our Design Check or send the CAD — our engineers flag missing draft, thin walls, and un-moldable features for free before any steel gets cut.
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