3D Printing, Product Development
5 Design Rules That Make or Break Your 3D Print
Category: 3D Printing, Product Development
We review hundreds of 3D print files every year. The same design mistakes show up again and again — and they’re almost always fixable with a few simple rules.
Whether you’re designing your own part in SolidWorks or sending us a file from another engineer, these five rules will save you time, money, and failed prints.
Rule 1: Respect Minimum Wall Thickness
Every 3D printing process has a minimum feature size. Go thinner and the part either won’t print or will be too fragile to handle.
Minimum wall thicknesses at PartSnap:
- FDM (ABS, PC-ISO, ULTEM): 0.045″ (1.14mm)
- SLA (Formlabs resins): 0.035″ (0.89mm)
- FFF (PLA): 0.040″ (1.02mm)
The common mistake: Designing 0.5mm walls because “it looks fine in CAD.” CAD doesn’t know your manufacturing process. A wall that renders beautifully on screen may be physically impossible to build.
The fix: Design to 1.5mm minimum for general-purpose walls. Go thinner only when you’ve confirmed the process can handle it.
Rule 2: Think About Orientation Before You Model
The orientation of a part on the build platform affects everything — strength, surface finish, support material, and cost. And orientation isn’t always obvious.
Key insight: 3D printed parts are strongest in the XY plane (within a layer) and weakest in Z (between layers). A hook that’s strong printed horizontally may snap when printed vertically.
The common mistake: Designing a part without considering how it will sit on the build platform. Then discovering that the only way to print it requires extensive support material — driving up cost and leaving marks on critical surfaces.
The fix: When you’re designing, ask yourself: “If this were sitting on a table, which face would be down?” Design your part so the most critical surfaces face up or sideways, and flat features face down.
Rule 3: Add Draft and Fillets Generously
Sharp internal corners are stress concentrators in any manufacturing process, but they’re especially problematic in 3D printing where layer adhesion is the weak link.
The common mistake: Sharp 90° internal corners everywhere. The part prints fine but cracks at those corners under load.
The fix: Add fillets to internal corners — even small ones (0.5–1mm radius) dramatically improve strength. External fillets improve surface finish too. If you’re designing for eventual injection molding, you’ll need draft angles anyway — add them now.
Rule 4: Design Clearances for Assembly
If two 3D printed parts need to fit together, the clearance between them matters more than you think. 3D printing has inherent dimensional variation, and parts that are “perfect” in CAD may not slide together in reality.
Recommended clearances:
- Press fit: 0.1–0.2mm interference (test first!)
- Sliding fit: 0.2–0.4mm clearance
- Loose fit / easy assembly: 0.5mm+ clearance
The common mistake: Designing mating features at nominal dimensions with zero clearance. The parts arrive and don’t fit.
The fix: Always add clearance. Start with 0.3mm for a general-purpose fit. Print a test piece before committing to a full build if fit is critical.
Rule 5: Hollow When You Can, Solid When You Must
Solid parts use more material, take longer to print, and cost more. Unless you need the structural mass, hollowing a part saves money without sacrificing function.
The common mistake: Sending a solid block when the design only requires a shell.
The fix: Shell your part in CAD to 2–3mm wall thickness. Add internal ribs for stiffness if needed. This can cut material usage (and cost) by 50–80% on large parts.
Exception: If the part needs to survive impact loading, or if internal geometry makes hollowing impractical, solid is fine. Just know you’re paying for it.
Not Sure If Your Design Is Print-Ready?
Send us your file. We review every submission for printability before quoting — and if something needs to change, we’ll tell you what and why. No charge for the review.
info@partsnap.com · 214.449.1455
PartSnap is a licensed Professional Engineering firm with in-house 3D printing in Dallas / Fort Worth, TX. We don’t just print files — we engineer parts. Learn more →