Draft Angle Explained
A draft angle is a slight taper on a vertical wall — a degree or two away from perfectly straight — so a part slides out of a mold, a die, or off a print bed without sticking or tearing. It is one of the simplest design-for-manufacturing rules, and ignoring it is one of the most common reasons a part comes back from a manufacturer as “not feasible.”
What draft angle means
Imagine a cup. The inside walls of a plastic cup are not perfectly vertical — they lean very slightly outward from bottom to top. That lean is the draft angle. Without it, the cup would grip the mold so tightly it would crack being pulled out.
Draft is measured in degrees from vertical. A 1° draft on a 30 mm tall wall adds about 0.5 mm of taper over the full height — barely visible, but enough to release cleanly.
Injection molding
This is where draft is non-negotiable. Parts with zero-draft vertical walls can seize in the tool. Standard: 1–2° for smooth surfaces, 3–5° for textured. Your mold maker will tell you their minimum.
3D printing (FDM)
Mostly optional for FDM — printed parts are removed by hand, not pulled from a steel tool. Draft does help on tall vertical towers that might warp or on lids that press into a housing; it is rarely a hard requirement.
Sand casting / urethane casting
1–3° per side. The rougher the pattern surface, the more draft you need to release it without tearing.
How much draft to add
A starting rule: 1° for every 25 mm of depth for smooth injection-molded surfaces. In practice, most short consumer parts use 1–2° and call it a day.
- 0.5–1° — minimum for polished mold surfaces (mirror finish).
- 1–2° — standard for most injection-molded parts.
- 3–5° — textured surfaces (grain patterns grip the wall).
- 5–10° — deep ribs, threads inside a mold cavity.
For 3D printing, if you do add draft, 1–2° is plenty. Anything more and the dimensional change is noticeable. See our guide on wall thickness for 3D printing for the companion DFM constraint.
When you can skip it
Draft is specifically a release constraint. If the part is:
- CNC machined — the cutter lifts out; no draft required. In fact, vertical walls are preferred (easier to program). See CAD for CNC machining.
- 3D printed for prototyping only — you pull the part off the bed; steep overhangs are the limit, not draft. If it needs supports, that is a different constraint.
- Laser cut or waterjet flat — 2D profile, no depth, no draft at all.
If the part will eventually go into production injection molding, design the draft in from the start. Retro-fitting draft into a mature design is painful — it changes every mating surface.
Add draft angle to your part
Describe the process to PartWork.ai — “add 2-degree draft to the outer walls” — and it will taper the faces. Check the result in the 3D viewer before exporting. For modifying an existing part, the taper operation adjusts the face angle in place. Export as STEP for a machine shop or as STL/3MF for printing — see exporting files.
Start with 2 free AI generations — no card required
Open the studio, describe your part with draft angles, and export for molding or printing. More credits: 100 for $4.99 (~5¢ each).