The Tier-1 Playbook: Plastic Part Design for Injection Molding

Designing parts for the injection molding process can be an intimidating and complex task. My years of product development experience showed me how quickly a simple oversight turns into a prohibitively expensive rework. From experience designing everything from Class-A painted exteriors, structural components, multi-material overmolds, complex assemblies spanning multiple tools and materials, and more, I found that design errors dominate as the reason for failed products, derailed programs, and massive budget overruns.

Being a manufacturing and design engineer with a lifetime of extensive hands-on experience across high-volume, high-stakes production environments in the automotive and defense sectors, I have seen the pitfalls and consequences of haphazard design practices. High-volume manufacturing has a knack for amplifying even simple design oversights into five or six-figure errors overnight. Having designed for nearly every major manufacturing process, the pattern became clear: the same core principles apply everywhere (high-volume or not) - robust geometry, disciplined tolerances, thoughtful material selection, and a relentless focus on manufacturability. In other words, smooth manufacturing and product launches only show up when the design respects the process.

This guide is the distilled result of that experience: 99 pages of practical rules, tables, and ratios with simple explanations of why they work. No academic theory, no endless standards, no unnecessary bloat: just the design practices that consistently deliver first-shot approval and eliminate expensive rework.

My goal is simple: Give designers, engineers, founders, and teams the guidelines to ship flawless parts without having to learn the hard (and excessively expensive) way. The rules in this guide were forged and tested in the crucible of high-volume manufacturing, a brutal proving ground, and became the gold standard for headache-free plastic part design. They will serve you well across every industry and application.

More Guesswork = More Rework | Design with Confidence

Who this is for:

This guide is for anyone who designs, reviews, or approves injection-molded plastic parts, regardless of industry or experience level.

• Entry-level designers and recent graduates: Get clear "what to do and why" explanations, tables, and rules to avoid common mistakes and build confidence fast.
• Experienced engineers: Use the printable reference tables for quick checks on walls, ribs, draft, tolerances, and features during design reviews.
• Startup founders and product developers: Avoid $50k–$200k mold rework on your first (or only) tooling run.
• Freelancers and consultants: Deliver Tier-1 quality to clients and justify your rates with proven rules.
• Procurement and program managers: Understand DFM to push back on risky designs and keep programs on schedule/budget.
• Teams in any industry: Automotive, medical devices, consumer electronics, industrial equipment; The rules were tested in high-volume environments, so they work reliably everywhere.

If you touch plastic parts and want to ship them flawless, first shot, this guide is your shortcut.

What you'll get:

• The 14 most common resins and their properties / use-cases
• Nominal wall, rib, boss, and gusset ratios that eliminate sink and warp
• Draft tables by texture depth
• Gate selection and vestige rules for cosmetic surfaces
• Commercial block tolerances per ISO 20457/DIN 16901
• Common design features with dimensions that pass first-shot sampling
• Steel-safe philosophy that prevents most post-tooling nightmares
• Printable reference tables for daily use
• Peace of mind when sending off your tooling kick-off package
• And much more...

Engineers, designers, startup founders, and procurement teams, from entry-level to senior, will find this reference invaluable.

Lifetime updates included. Instant download.

If you've ever lost sleep over a mold rework or hesitated to press send on your tooling kick-off package, this guide is your shortcut to confidence.

-The Tier-1 Engineer