Injection Molding Draft Angle Rules for Device Housings

Concept render

Most molder guides start at 0.5 degrees on vertical faces and 1 to 2 degrees for most walls, plus about 1 degree per inch of cavity depth. Textured faces need more: Protolabs requires 3 degrees for a light texture and 5 or more for a heavy one. Ribs, bosses, snap fits and shutoffs need draft too.

Draft is the small taper on every face that runs parallel to the direction the mold opens. It lets the part slide off the core without drag marks, sticking or warping. Small device housings get it wrong in predictable places: textured outer shells, short inner walls, screw bosses and snap fits. This guide collects the numbers that public molder design guides publish, shows where they disagree, and turns them into a review you can run before the tool is cut.

Every guideline comes from the Protolabs, Fictiv and Xometry pages in the sources, read on November 5, 2026. Each is that company's guideline for its own process. The offset table and one ratio conversion are our arithmetic. Your molder's DFM report has the final say. This article contains no Duobay price and no test result.

What injection molding draft angle does a small device housing need?

For a smooth wall on a small housing, the guides agree on a starting range of 1° to 2°. Protolabs adds a floor of 0.5° on all vertical faces. If your walls are well under 1 inch tall, the 1° per inch depth rule rarely pushes the number up. The finish does. Protolabs asks for 3° on a light bead-blast texture and 5° or more on a heavy one, and that is the number that changes your industrial design.

Agree on the pull direction and the parting line with the molder before you add draft. A face drafted the wrong way acts like an undercut.

What do molder draft angle guidelines say?

Here are the published draft angle guidelines side by side, as of November 2026. Where two sources give different numbers, both are shown.

The resin changes the number too. Fictiv publishes a minimum and a recommended draft for common materials, as of November 2026. If your housing is polycarbonate, note that Fictiv puts PC at the strict end of its table. ABS and PC/ABS are not in the table, so ask your molder for those.

Source: Fictiv, Draft Angle Guidelines for Injection Molding (page dated January 19, 2024), as of November 2026.

How much extra draft does a textured surface need?

Texture adds tiny peaks and pits to the mold wall. The part has to slide past them on ejection, so a textured face needs more taper than a smooth one. The guides tie the extra draft to texture depth, and they do not agree on the ratio.

Sources: Fictiv draft guide, Xometry, An Overview of Injection Molded Surface Finishes (updated May 14, 2025), Protolabs, Mold Texture Standards and Finishes, all as of November 2026. The per-0.001 in conversion of the Protolabs ratio is our arithmetic.

The spread matters on a 0.002 in texture: 3° by one rule, close to 4° by the other. Pick the texture first, then take the draft from the chart of the shop that will texture the tool. Write that number and its source on the drawing next to the finish callout.

How do you turn a draft angle into a dimension?

Draft moves each face by the wall height times the tangent of the angle. The table below is plain trigonometry. It shows how far one side moves in from the base to the top of the wall.

On a 10 mm tall wall with a 5° textured finish, each side moves about 0.87 mm. A housing with two drafted sides loses about 1.75 mm of width across its height. If the inner wall follows the outer one, the cavity shrinks by the same amount. That can clip a battery corner or PCB edge that fit in the undrafted CAD.

Protolabs suggests keeping the inner and outer walls of an enclosure parallel and using a core-cavity layout, so wall thickness stays even (Protolabs draft tips, as of November 2026).

Where do designers forget draft?

Outer walls rarely get missed. The small features inside the shell do.

Ribs and gussets

Fictiv says all vertical features, including ribs and bosses, need adequate draft. Protolabs warns that tall ribs and thick standoffs are problem areas and may need up to 3° or more to avoid ejection trouble (Protolabs complex features, as of November 2026).

Screw bosses

Protolabs says a boss needs draft on both its inside and outside walls, from 0.5° to 3° depending on height. It also suggests boss walls of 40 to 60 percent of the wall they rise from, and tying a boss to a nearby wall with ribs instead of filling the gap solid (Protolabs boss design, as of November 2026). Draft on the inner bore changes the diameter along its depth, so dimension the pilot hole at a stated depth and check screw engagement there.

Snap fits and clips

Protolabs says snaps are best made with a sliding shutoff, which needs the feature aligned with the direction of mold opening, a relief hole at the base of the clip, and possibly extra draft (Protolabs complex features, as of November 2026). On a small device that hole may land on a cosmetic face. Decide early whether you accept it or pay for a slide in the tool. Our guide to undercuts and snap fit design compares slides, lifters and design-out options.

Shutoffs, holes and openings

Where metal slides on metal in the tool, a shutoff, Protolabs sets 3° as the minimum. Fictiv says designers typically apply 5° to 7° to shut-off surfaces where the parting line steps (Fictiv draft guide, as of November 2026). Ask the molder which openings, such as button holes and port cutouts, will be formed by a shutoff, and check those alongside the IP and seal design. Our guide to IP67 and IP68 tracker enclosures covers the seal side.

Press-fit holes

Draft that helps ejection can loosen a press fit. Protolabs suggests a drafted hole with three or more undrafted crush ribs along its length, which give a tight fit and good alignment (Protolabs crush ribs, as of November 2026). This suits light pipes, magnets and alignment pins in small housings.

How should you review draft before the tool is cut?

Draft is cheap to fix in CAD and slow to fix in a cut tool. Run this review at the end of the enclosure design, before you release files for tooling. For where this sits in the build stages, see what you get at EVT, DVT and PVT.

Prototype tools need their own check. Protolabs says an aluminum mold may need extra draft and wall thickness because of the end mills used to cut it (Protolabs draft tips, as of November 2026). If your first small batch comes from an aluminum tool, ask the molder whether the draft that suits steel also suits that tool.

What should you ask your hardware team about draft?

Take this list to your mechanical engineer and to the molder that quotes the tool.

• Which way does the mold open, and has the molder confirmed it?
• What draft did we target for each finish, and where did each number come from?
• Which texture is on each outer face, and what does its chart require?
• Did we check PCB, battery and display clearance at the narrow end of each pocket?
• Which faces have less than 0.5°, and who signed off on them?
• Which snaps need a slide, and is the hole under each snap acceptable on the cosmetic side?
• Will the prototype tool be aluminum, and does it need extra draft?

To see how mechanical design, tooling and test fit into the wider build, read how the mechanical work is organized.

What else do teams ask about draft angles?

If you want your housing reviewed for draft, texture and tooling before you commit to a mold, tell us about your device.

Sources

All pages accessed November 5, 2026. Confirm with your molder before you rely on any figure.

• Protolabs, Draft Angle Guidelines for Injection Molding
• Protolabs, Plastic Injection Molding Design Guidelines
• Protolabs, Mold Texture Standards and Finishes
• Protolabs, Plastic Boss Design on Molded Parts
• Protolabs, 5 Ways to Master Complex Features in Injection-Molded Parts
• Protolabs, Adding crush ribs to molded parts
• Fictiv, Draft Angle Guidelines for Injection Molding
• Xometry, An Overview of Injection Molded Surface Finishes