When you’re 3D printing parts—whether for prototypes or functional components—getting the right size matters. Even a tiny dimensional error can break a product, delay a project, or waste money. That’s where 3D printing tolerances come in. This guide breaks down what tolerances are, the key factors that affect them, how different 3D printing technologies stack up, and practical tips to ensure your parts meet your specs. We’ll use real data from industry leaders like Zemi Technology to keep things grounded.
What Are 3D Printing Tolerances?
Let’s start with the basics: tolerance in 3D printing is the allowed difference between the dimensions of your CAD model (what you design) and the physical part (what you print). For example, if you design a 100mm bolt, a tolerance of ±0.2mm means the printed bolt can be between 99.8mm and 100.2mm and still work.
Unlike CNC machining, which has clear international tolerance standards, 3D printing has no global rules as of 2021. This makes understanding what drives tolerances even more important—because it lets you predict and fix issues before they happen.
Every 3D printed part has some tolerance variation. The goal isn’t zero tolerance (which is impossible and expensive) but to match the tolerance to your project’s needs. A toy prototype might need looser tolerances than a medical device component, for instance.
Key Factors That Affect 3D Printing Tolerances
Four main factors determine how accurate your 3D printed parts will be. Let’s break each one down with examples and data to show their real impact.
1. Material Shrinkage
All 3D printing materials—from thermoplastic filaments to metal powders—shrink as they cool or cure. This shrinkage changes the part’s final size, and uneven shrinkage can cause warping (twisted or bent parts).
- Why it happens: Polymers (plastics) naturally shrink when they go from liquid/molten to solid. Metals shrink too, but at different rates than plastics.
- Real-world example: A PLA filament part might shrink 1-2% during cooling, while a metal like Stainless Steel 17.4 could shrink 5-7% in SLM printing. If you design a 200mm plastic bracket, 2% shrinkage would make it 196mm—too small for a tight fit.
- Warping risks: Parts with thick geometries (like a 10mm solid block) or uneven wall thicknesses (e.g., 2mm in one area, 5mm in another) are more likely to warp. Cheap, low-quality plastics also have unpredictable shrinkage, making them bad for precise parts.
2. Layer Thickness (Resolution)
Layer thickness is the height of each layer the printer adds—think of it as the “pixels” of 3D printing. It directly affects tolerance, especially in the Z-axis (vertical direction).
- How it impacts accuracy: Thinner layers (e.g., 0.02mm) mean smoother surfaces and tighter tolerances, but they take longer to print. Thicker layers (e.g., 0.3mm) are faster but can create “stepped” edges on curved parts (called the layer staircasing effect), which deviate from your design.
- Technology differences:
- FDM and SLA printers: Layer thickness is adjustable, so you can trade speed for accuracy. A desktop FDM printer might have inconsistent layer heights (leading to size errors), while industrial FDM printers (like those from Stratasys) maintain tighter control.
- SLS and DMLS printers: Layer thickness is often preset by the manufacturer (e.g., 0.08mm for SLS), so tolerance is more consistent.
3. Minimum Feature Size
Minimum feature size is the smallest detail the printer can reliably print—like a tiny hole, a thin wall, or small text. If your design has features smaller than this, the part will have tolerance issues.
- What drives it:
- FDM: Nozzle diameter (e.g., a 0.4mm nozzle can print walls as thin as 0.4mm, but 0.8mm is safer for accuracy).
- SLA/SLS/DMLS: Laser beam diameter (e.g., a 0.05mm laser can print finer details than a 0.1mm laser).
- Example: If you design a 0.3mm hole in an FDM part with a 0.4mm nozzle, the printer will likely fill the hole or make it too big—ruining the part’s function (like a missing screw hole).
4. Build Size
Build size is the maximum size of the part the printer can handle. Larger parts have looser tolerances because they take longer to cool/cure, leading to more shrinkage and warping.
- Cooling time effect: A 500mm aerospace bracket in FDM printing might take 8+ hours to print. During that time, the bottom layers cool completely while the top layers are still molten—creating stress that warps the part.
- Support structure impact: Large parts need more support (e.g., a tall 300mm column needs support to stay upright). Removing supports can scratch the part or remove material, changing its dimensions. For example, a supported edge might lose 0.5mm of material when supports are peeled off.
Tolerances by 3D Printing Technology
Not all 3D printing technologies have the same tolerances. Below is a detailed table of key specs for the most common technologies, using data from Zemi Technology. This will help you choose the right tech for your tolerance needs.
| Technology | Tolerance Range | Build Volume (Max) | Layer Thickness | Minimum Feature Size | Best For |
| HP Nylon Multi-Jet Fusion (MJF) | ±0.3% (±0.2mm per 100mm) | 380 x 284 x 380mm (recommended: 356 x 280 x 356mm) | ~0.08mm | Min: 0.5mm; Recommended: 0.7mm | Functional plastic parts (e.g., gears, enclosures) |
| Laser Sintering (SLS) | ±0.3% (±0.3mm per 100mm) | 350 x 350 x 400mm | ~0.1mm (1.5mm for waterproof parts) | Min: 0.6mm; Recommended: 1.0mm | Durable prototypes, low-volume production |
| Resin Light Curing (SLA) | ±0.2% (±0.2mm per 100mm) | 736 x 635 x 533mm (varies by material) | ~0.02mm | Min: 0.5mm; Recommended: 0.8mm | High-precision parts (e.g., jewelry, dental models) |
| FDM (Thermoplastic) | ±0.3% (±0.3mm per 100mm) | 914 x 610 x 914mm (varies by material) | 0.05–0.3mm | Min: 0.4mm; Recommended: 0.8mm | Large parts, mechanical components (e.g., brackets) |
| Metal Laser Sintering (SLM) | ±0.2% (±0.1–0.2mm per 100mm) | 276 x 276 x 350mm | 0.02–0.08mm (varies by material) | Exterior: 0.75mm; Structural: 1.5mm | High-strength metal parts (e.g., aerospace components) |
Example: Choosing Tech for Tolerance Needs
If you need a 200mm medical part with a tolerance of ±0.3mm:
- SLA (±0.2mm per 100mm) would give you ±0.4mm for 200mm—close enough.
- FDM (±0.3mm per 100mm) would give you ±0.6mm—too loose.
So SLA is the better choice here.
How Post-Treatment Affects Tolerances
Post-treatment (the steps you take after printing) can either fix or ruin tolerance. Here’s how common processes impact accuracy:
- Support removal: Most technologies (FDM, SLA, SLM) use supports. Removing them with pliers or a knife can scratch the part or leave gaps. For example, an SLA part with supports on its edge might lose 0.2mm of material when supports are cut off.
- Sanding/Polishing: Sanding can smooth surfaces but also remove material. If you sand a 10mm plastic part too much, it might become 9.8mm—out of tolerance.
- Coating/Painting: Coatings (like epoxy) or paint add thickness. A 50mm metal part with a 0.1mm coating becomes 50.2mm—good if you need a tighter fit, but bad if you need precision.
- Heat Treatment (for metals): SLM/DMLS parts often need heat treatment to reduce stress. This can cause slight shrinkage (e.g., 0.5% for AlSiMg Aluminum), so you’ll need to adjust your design to account for it.
Yigu Technology’s Perspective on 3D Printing Tolerances
At Yigu Technology, we know tolerances make or break 3D printing projects. Our advice? Start with “tolerance-first” design: match your material, technology, and post-treatment to your accuracy needs. For example, if you’re printing a high-precision automotive sensor, use SLA (tight tolerance) with a 0.02mm layer thickness and minimal supports. For large industrial brackets, FDM works—just choose a low-shrinkage material like ULTEM 1010. We also recommend testing small prototypes first: a 50mm test part lets you adjust tolerances before printing full-size components. With our network of manufacturers, we help clients balance tolerance, cost, and speed to get parts that work every time.
FAQ:
1. Can I get zero tolerance in 3D printing?
No—zero tolerance (perfectly matching your CAD model) is impossible in 3D printing. Even the best technologies (like SLA or SLM) have small variations. Instead, focus on “functional tolerance”: the tolerance your part needs to work. For example, a toy wheel might need ±1mm, while a medical implant needs ±0.1mm.
2. How do I adjust my design to account for material shrinkage?
Most 3D printing software (like Fusion 360 or Simplify3D) lets you scale your model to offset shrinkage. First, find your material’s shrinkage rate (e.g., 2% for PLA). Then scale your CAD model by 102% (100% + 2%) before printing. For example, a 100mm PLA part scaled to 102mm will shrink to ~100mm after cooling.
3. Which technology is best for tight tolerances (±0.1mm per 100mm)?
SLM (metal) and SLA (resin) are the top choices. SLM has a tolerance of ±0.1–0.2mm per 100mm, making it great for metal parts like aerospace components. SLA has a tolerance of ±0.2mm per 100mm, which is ideal for high-precision plastic parts like dental models. Avoid desktop FDM printers for tight tolerances—they often have inconsistent layer heights and material shrinkage.
