Ask any seasoned mold designer, and they’ll tell you that a bad CAD file is like a ticking time bomb. It might look great on your monitor, but the moment it leaves the comfort of your desktop and steps into the real world of steel, tooling, and production—it detonates.
Suddenly, you’re facing delays, budget overruns, and features that defy physics. At H&H Molds, we’ve been handed our fair share of digital disasters—so if your part’s future depends on a mold, please read on.
This simple guide will help you steer clear of the most common CAD catastrophes we’ve encountered through many decades in the plastic molding industry.
The “Near Enough” Geometry
Sometimes, parts arrive looking like a geometry student’s group project—close but nowhere near production-ready. We see faces that almost touch, edges that should align but don’t, and fillets that seem to exist for decoration rather than function. These gaps might not be visible on your screen, but they can become massive headaches when steel meets plastic. Mold flow analysis gets thrown off. Tool paths become unpredictable. Worst case? A tool gets built around bad geometry, and now you’re burning time (and money) on rework.
Pro Tip: Don’t rely on visual inspection alone. Use mating part references, double-check tangencies, and validate tolerances against real-world fit. When in doubt, loop in your mold shop before finalizing the design.
Features That Can’t Be Milled (Without Magic)
It’s incredible how many CAD files we receive that assume our tooling department moonlights at Hogwarts. Deep, blind-side undercuts. Needle-thin ribs with no draft. Floating islands of geometry that have no clear shutoff or tooling path. Sure, it looks sleek in SolidWorks—but when we try to fixture or cut that shape into hardened steel, physics has the final say.
Pro Tip: Know your limits. The more complex the geometry, the more likely it is to require additional mold actions (and costs). A brief DFM review early on can highlight features that are either cost drivers or outright showstoppers.
Metric Mayhem Meets Imperial Insanity
You wouldn’t install a speedometer in kilometers and set the cruise control in miles per hour—but somehow, we still get files with that level of confusion. It’s not just a rookie mistake, either. Even seasoned engineers slip into unit chaos: modeling in mm, dimensioning in inches, and leaving the shop floor to sort it out. If your vendor has to guess what you meant, you’ve already lost control.
Pro Tip: Choose a unit system and adhere to it consistently throughout your model, drawings, and tolerances. Include a detailed drawing package with material specs, surface finish requirements, and wall thicknesses. It saves questions—and saves face.
Unclear Revision History
Nothing burns goodwill faster than this: we quote off Rev B, build to Rev C, and then receive an email stating that Rev D was approved yesterday. Without a clear audit trail, your project quickly turns into detective work. That’s not just annoying—it’s dangerous. Changes to wall thickness, radii, or hole positions—if undocumented—can destroy timelines and confidence.
Pro Tip: Keep revision control tight. Always label file versions clearly, include a changelog, and avoid renaming files like “final_final_2.STEP.” Your mold shop should never have to guess which version is the correct file to build to.
Missing Draft Angles—Again
We shouldn’t even need to say this anymore. Yet here we are—reviewing models with vertical walls that pretend gravity doesn’t exist. No draft = no eject. Even one or two degrees of taper can mean the difference between smooth ejection and a part that clings like static.
Pro Tip: Every vertical face needs a draft. The amount depends on the resin and surface finish, but zero is never the correct number. If you’re unsure, we’ll provide you with the exact requirements for your application.
Why Any of This Matters
Every bad CAD file has a cost—and it’s rarely just time. It’s almost always going to mean a rework. Missed deadlines. Frustrated teams. Damaged trust. Fixing those issues after the steel is cut? That’s the most expensive lesson in the business.
That’s why H&H Molds offers complimentary DFM reviews upfront. We’ve already seen the worst—so you don’t have to learn the hard way.
Want your next part to get off to a strong start? Please send us your latest CAD using our Free Quote form. We’ll make sure your file isn’t destined for the “hall of shame.”
Want to keep reading? We found an interesting article from PlasticsTechnology magazine about the most challenging CAD designs that injection molders have encountered.
