5 Common 3D Printing Mistakes (And How to Avoid Them)

3D printing has become incredibly accessible, but there's still a learning curve. Whether you're printing at home or ordering parts from a service, understanding these common pitfalls will save you time, money, and frustration. Here are five mistakes we see regularly — and how to avoid them.

1. Poor Bed Adhesion (The Print Comes Loose Mid-Print)

Nothing is more frustrating than coming back to your printer and finding a tangled mess of spaghetti plastic where your print should be. Poor bed adhesion is the number one cause of failed prints, and it's almost always preventable.

Common causes:

• Bed not level: If the nozzle is too far from the bed, the first layer won't squish down and stick. Too close and the filament gets scraped off. Get the first layer right and most prints will succeed.
• Bed temperature too low: Different filaments need different bed temperatures. PLA can print on a cold bed, but PETG and ABS absolutely need heat.
• Dirty build plate: Fingerprints, dust, and residue from previous prints reduce adhesion. Clean your bed regularly with isopropyl alcohol (IPA).
• No adhesion aid: For tricky materials, use a glue stick, hairspray, or a textured PEI sheet. These provide a grip surface for the first layer.

The fix:

Level your bed carefully, use the correct temperature for your filament, keep the surface clean, and use a brim or raft for parts with small contact areas. A good first layer is the foundation of every successful print.

2. Choosing the Wrong Infill Percentage

Infill is the internal structure of a 3D print — the grid or pattern inside the solid outer walls. New users often default to high infill (50–100%) thinking it makes parts stronger, or very low infill (5–10%) to save time. Both extremes cause problems.

The issue:

• Too high (50–100%): Wastes filament, dramatically increases print time, and doesn't improve strength as much as you'd expect. Most of a part's strength comes from its wall thickness, not infill.
• Too low (0–10%): Top layers can sag or show through (called "pillowing"), and the part may be too weak for any functional use.

The fix:

For most parts, 15–25% infill with 3–4 wall layers is the sweet spot. This gives good strength, reasonable print times, and clean surfaces. If you need more strength, increase wall count before increasing infill — walls contribute far more to structural integrity than infill does.

For purely decorative parts (vases, display models), you can use as little as 10%. For functional load-bearing parts, 30–40% with extra walls is usually plenty.

3. Forgetting About Supports (Or Using Them When You Don't Need Them)

3D printers build layer by layer from the bottom up. This means any part of your design that overhangs beyond about 45 degrees needs support material beneath it — otherwise you're printing into thin air and the filament will droop.

Common mistakes:

• No supports on obvious overhangs: Bridges and overhangs past 45° will droop, sag, or fail completely.
• Supports everywhere: Automatic support generation can add supports in places they're not needed, wasting material and leaving ugly marks where they're removed.
• Not considering print orientation: Often you can rotate a part so it needs fewer or no supports. A bracket printed on its side might need zero supports, while printing it upright might need support everywhere.

The fix:

Before hitting print, preview the sliced model and check where supports are placed. Consider rotating the part — the best orientation minimises supports while keeping critical surfaces facing up or outward. Use tree supports (available in most slicers) for organic shapes — they're easier to remove and leave cleaner surfaces.

When designing parts for 3D printing, try to avoid overhangs greater than 45° where possible. Chamfers instead of fillets on bottom edges, self-supporting angles, and strategic part orientation can eliminate the need for supports entirely.

4. Ignoring Layer Height Trade-offs

Layer height is one of the most impactful settings in your slicer, and choosing the wrong value for your application wastes either time or quality.

The trade-off:

• Fine layers (0.08–0.12mm): Smooth surfaces, near-invisible layer lines, but extremely slow. A part that takes 2 hours at 0.2mm might take 6–8 hours at 0.1mm.
• Standard layers (0.2mm): Good balance of speed and quality. Visible layer lines but generally acceptable for functional parts.
• Thick layers (0.28–0.32mm): Fast but rough. Visible stair-stepping on curved surfaces. Fine for internal parts or rough prototypes.

The fix:

Match the layer height to the purpose:

• Display models, miniatures, cosplay: 0.08–0.12mm for smooth surfaces
• General purpose, functional parts: 0.16–0.20mm (the best all-round choice)
• Rough prototypes, internal brackets, test fits: 0.24–0.32mm for speed

Many slicers also support variable layer height — using fine layers on curved surfaces and thick layers on straight walls. This gives you the best of both worlds.

5. Not Doing a Test Print

This one sounds obvious, but it catches people out constantly — especially when ordering parts from a printing service or when a design will be reproduced in quantity.

What goes wrong:

• Tolerances are off: Holes are too tight, snap-fits don't snap, parts that should fit together don't. 3D printers have dimensional tolerances of ±0.2–0.5mm, and this matters for assembly.
• The design doesn't print well: Thin walls break, overhangs sag, or the part warps. What looks fine in CAD doesn't always survive the printing process.
• Scale issues: The model was designed in inches but sliced in millimetres (or vice versa). The resulting print is either tiny or enormous.

The fix:

Always print a single test piece before committing to a full batch. For parts that need to fit together, print the mating surfaces first as a quick test — you don't need to print the entire part. Add 0.2–0.3mm of clearance to any holes or slots that need to accept another part.

If you're ordering from a service like RBZ 3D, we'll flag potential issues before printing. But it's always worth ordering a single prototype first, verifying the fit, and then ordering the full batch.

Summary

Most 3D printing failures come down to a few preventable mistakes:

1. Get your first layer right — clean bed, correct temperature, proper levelling
2. Use 15–25% infill with extra walls instead of high infill
3. Think about orientation and supports before slicing
4. Match layer height to the purpose of the part
5. Always test before committing to a batch

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