How Do You Control Shrinkage in 3D Printing?

Introduction
You design a part to be 100.0 mm long. You print it, and it measures 99.5 mm. This is material shrinkage, and it can ruin your project’s fit and function. Shrinkage is a physical fact in 3D printing. But you can predict it, plan for it, and control it. This guide explains why plastic and resin shrink. It shows you the shrinkage rates for common materials. It gives you a clear plan to get the right size every time. Let’s solve the shrinkage problem.

What Is Material Shrinkage?

Shrinkage is the size reduction of a part as it cools or cures. When you heat plastic to melt it, it expands. When it cools on the print bed, it contracts. The same happens with resin: liquid turns to solid, taking up less space.

What Causes the Shrinkage?

Three main factors drive the change:

1. Thermal Contraction: Hot material takes more space. As it cools, molecules move closer. This causes volume loss.
2. Curing Shrinkage (Resin): UV light links liquid resin molecules into a solid polymer network. This process pulls material inward.
3. Internal Stress: Different parts of your print cool at different speeds. This uneven cooling creates pull forces inside the part, warping edges and changing size.

Key Term: The Coefficient of Thermal Expansion (CTE) measures how much a material grows with heat. A high CTE means more shrinkage as it cools.

Real Case: A team printed a large ABS housing. The room was cold. The bottom layers cooled fast, the top stayed hot longer. This stress made the part warp up at the corners and shrink more than 1% in length. The part did not fit.

How Much Do Common Materials Shrink?

Each material has a typical shrinkage range. Knowing this helps you pick the right one.

What Are the Numbers?

See this table for key data.

Example: A 200 mm long part in ABS could shrink up to 1.6 mm (0.8% of 200 mm). The same part in PLA might only shrink 1.0 mm.

Why Do Resins Shrink More?

Resin shrinkage is mainly chemical, not thermal. Liquid resin molecules are far apart. When UV light cures it, they form tight bonds. This polymerization pulls the structure inward much more than cooling plastic. This is why resin prints need more compensation.

How Can You Predict Shrinkage?

You need to know the exact rate for your material, your printer, and your settings.

Can You Rely on Vendor Data?

Vendor data is a good start, but it’s a range from lab tests. Your real rate depends on your print environment. Always run a calibration test.

How to Run a Shrinkage Test?

Print a simple test cube (e.g., 50 x 50 x 10 mm). Use your normal settings.

1. Let the part cool fully (for 24 hours).
2. Measure each side with calipers.
3. Calculate: Shrinkage % = [(Design Size – Actual Size) / Design Size] x 100.

Do this test for each new spool or resin bottle. Humidity and age change material behavior.

Pro Tip: Print the test part flat on the bed. Do not use a raft. This gives the most true size reading.

What Are the Main Control Methods?

You have four powerful tools to fight shrinkage: Design, Material Choice, Print Settings, and Post-Process.

Can Design Fix Shrinkage?

Yes. Use shrinkage compensation (scaling) in your slicer or CAD model.

• If your test shows 0.6% shrinkage, scale the model up by 1.006x (100.6%).
• For resin, you may need to scale by 1.02x to 1.035x.

Important: Scaling works best for simple, solid shapes. For very complex parts with thin walls, scaling can distort details. Test on a small section first.

How Does Material Choice Help?

Pick a material with low inherent shrinkage for critical dimensions.

• For FDM, PLA is the most stable. Use it when size is key.
• For resin, choose low-shrink or “engineering” resins. They cost more but change less.

Case Study: A watch designer needed a precise casing prototype for fit check. They first used standard resin. Shrinkage was 3%, ruining the tolerance. They switched to a low-shrink dental model resin (1.2% shrinkage). The next print fit perfectly.

What Print Settings Reduce Shrinkage?

Tune your machine to promote even, slow cooling.

For FDM Printers:

• Lower Nozzle Temp: Use the lowest temperature that gives good layer bond. High temp means more expansion, then more contraction.
• Use a Heated Bed & Enclosure: Keep the part warm as it builds. This reduces the temperature gradient. For ABS, use a bed at 100-110°C inside a closed chamber.
• Slower Print Speed: This allows more even cooling between layers.
• Optimize Infill: High infill (80-100%) has more material to shrink, causing more pull. Use the minimum infill your part needs for strength. 20-40% is often enough.

For Resin Printers:

• Post-Cure Slowly: Do not cure a wet part under strong UV right away. Let it dry fully, then cure in warm water (30-40°C). This reduces stress.
• Orient Parts Smartly: Place the part at an angle. This spreads shrinkage forces, preventing big warp on one side.

Does Post-Processing Help?

Yes, you can fix small errors after printing.

• Heat Treatment (Annealing): For FDM parts (PLA, ABS, Nylon). Bake the part in an oven at a set temperature (e.g., 80°C for PLA). This relaxes internal stress and can make size more stable. Warning: Annealing can also cause new shrinkage of 1-2%. You must test and compensate for this too.
• Conditioning: For Nylon, storing the part in a dry box for a few days lets it reach a stable size.

What About Warping and Cracking?

Shrinkage does not just make parts smaller. It causes warping, layer splitting, and cracks.

Why Do Corners Lift?

The bottom layer cools fast and sticks to the bed. The top layers are hot. As they cool, they contract and pull the edges up. This is classic warping.

Solutions:

• Use a brim (5-10mm wide) around the part. It holds edges down.
• Apply adhesive like glue stick or hairspray on the bed for better grip.
• Ensure your first layer is perfectly squished and flat.

What Causes Cracks Between Layers?

If one layer cools and shrinks fast, it pulls away from the hot layer above. This creates a weak bond or crack.

Solutions:

• Increase printing temperature slightly for better layer fusion.
• Use an enclosure to keep the whole part warm during the print.
• Choose a material with lower shrinkage, like PETG over ABS for large parts.

Is Shrinkage Always Bad?

Not always. In some cases, you can use it. Press-fit and snap-fit joints rely on a tiny bit of shrinkage for a tight grip. Design the joint with a 0.2-0.5 mm interference. The shrinkage will make the final fit perfect.

Example: A snap clip was designed with 0.3 mm extra width. After PLA shrinkage, the clip fit snugly onto a 10.0 mm rod without being loose.

How Do You Create a Reliable Process?

Follow this step-by-step plan for any new project.

1. Define Your Tolerance: How precise does the part need to be? ±0.1 mm? ±1 mm?
2. Pick Your Material: Choose based on your tolerance and part function. Use the shrinkage table.
3. Run Calibration Tests: Print a test cube with your chosen material and settings. Measure and calculate the real shrinkage rate.
4. Compensate in Your Model: Scale your final design in the slicer by your measured rate.
5. Optimize Print Settings: Set the right temperatures, use an enclosure, add a brim.
6. Post-Process if Needed: Anneal the part if required for stability. Measure again after.
7. Document Everything: Keep a log of material, settings, and results. This builds your own knowledge base.

Conclusion

Shrinkage in 3D printing is a predictable force, not a random error. PLA and low-shrink resins offer the most size stability. You can control shrinkage through smart design scaling, careful material choice, and controlled print settings. Always run a real-world calibration test for critical dimensions. Remember that post-processing like annealing can also change size. By understanding and planning for shrinkage, you move from failed prints to precise, reliable parts every time.

FAQ

Can I just scale up every model to fix shrinkage?
Scaling is a good tool, but not perfect. It works best for simple, solid shapes. For complex parts with holes and thin walls, scaling can distort them. Always test a small sample with your exact settings first.

Does a heated bed stop shrinkage?
A heated bed reduces warping and uneven shrinkage by keeping the bottom layers warm. It helps a lot, but it does not stop the overall size change from cooling. You still need to compensate for the total shrinkage.

Why does my part shrink more in one direction?
This is anisotropic shrinkage. In FDM, layers bond is weaker in the Z-axis (vertical). The part may shrink more across layers (X/Y) than between layers (Z). In resin, light sources can cause uneven cure. To fix, run tests in all three axes and compensate differently if needed.

How long should I wait to measure a part?
Wait at least 24 hours for FDM parts to fully cool and stabilize. For resin, wait until it is fully dry and post-cured. Measuring too soon gives wrong numbers.

Is there a material with zero shrinkage?
No. All materials change size with temperature or phase change. Some filled materials (like carbon-fiber PLA) shrink less because the fibers resist contraction. But zero shrinkage is not physically possible with current 3D printing tech.

Discuss Your Projects with Yigu Rapid Prototyping

At Yigu, we tackle dimensional accuracy daily. Our process starts with material characterization: we test every filament and resin batch to know its exact shrinkage under our print conditions. We then apply custom scaling factors in our pre-production workflow. For a client needing a set of interlocking gears, we used this method to achieve a fit tolerance of ±0.05 mm across ten parts. We also offer precision annealing services for FDM parts to lock in final dimensions. If your project demands exact sizes, let’s discuss how to build predictability into your 3D printing process from the start.