Why is my PLA cracking?

Cracking in your PLA (polylactic acid) prints can be a frustrating issue, often caused by improper printing temperatures, insufficient bed adhesion, or environmental factors like drafts. Addressing these elements is key to achieving smooth, durable PLA prints.

Why Is My PLA Print Cracking? Understanding the Causes

Experiencing cracking PLA prints is a common challenge for 3D printing enthusiasts. This phenomenon can stem from a variety of factors, ranging from the settings on your 3D printer to the environment in which you’re printing. Understanding these root causes is the first step toward achieving successful prints.

Temperature Troubles: The Impact of Printing Heat

One of the most frequent culprits behind cracking is incorrect printing temperature. PLA, while relatively easy to print, has specific temperature requirements that must be met. If the nozzle temperature is too low, the plastic won’t melt sufficiently, leading to poor layer adhesion. Conversely, if it’s too high, the material can degrade.

Nozzle Temperature: Aim for the manufacturer’s recommended range, typically between 190-220°C.
Bed Temperature: While PLA doesn’t strictly require a heated bed, a temperature of 50-60°C can significantly improve adhesion and prevent warping, which can lead to cracks.

Bed Adhesion Blues: When Prints Don’t Stick

A strong first layer is crucial for any 3D print. If your PLA print isn’t adhering well to the print bed, it can lift and warp, creating stress points that eventually lead to cracking. This is especially common on larger prints.

Clean Print Surface: Ensure your print bed is free of dust and oils. Isopropyl alcohol is excellent for cleaning.
Leveling: A properly leveled bed ensures consistent contact across the entire surface.
Adhesion Aids: Consider using a glue stick, hairspray, or specialized build surface adhesives if you’re having persistent adhesion issues.

Environmental Factors: The Unseen Influences

The environment where your 3D printer operates plays a surprisingly significant role. Sudden temperature changes or drafts can cause rapid cooling of the printed layers, leading to shrinkage and stress.

Drafts: Avoid placing your printer near open windows, fans, or air conditioning vents.
Enclosures: Using an enclosure can help maintain a stable, warm printing environment, reducing the risk of thermal shock and cracking. This is particularly beneficial in cooler rooms.

Material Quality and Storage: The Filament’s Story

Not all PLA is created equal. The quality of the filament itself, and how it’s stored, can impact printability.

Moisture Absorption: PLA is hygroscopic, meaning it absorbs moisture from the air. Wet filament can cause popping and sizzling during printing, leading to weaker layers and potential cracks. Always store PLA in a dry environment, ideally in a sealed bag with desiccant.
Filament Quality: Lower-quality PLA might have inconsistent diameter or impurities, which can lead to extrusion problems and weaker prints.

Troubleshooting Common PLA Cracking Scenarios

Let’s look at some specific situations and how to address them.

Scenario 1: Cracks Appearing on the First Few Layers

If your print cracks very early on, it’s almost certainly an issue with bed adhesion or warping.

Action: Re-level your bed, clean the surface thoroughly, and consider using an adhesion aid. Ensure your initial layer is printing slowly and at the correct temperature.

Scenario 2: Cracks Developing on Tall, Thin Prints

Tall prints are susceptible to cooling too quickly. The upper layers cool faster than the lower ones, causing shrinkage and stress.

Action: Reduce your part cooling fan speed, especially for the initial layers. Consider using an enclosure to maintain ambient temperature. Printing slower can also help.

Scenario 3: Cracks Appearing After the Print is Complete

This can sometimes be due to internal stresses built up during printing, or post-print handling. If the print is removed from a heated bed too quickly while still warm, it can warp and crack.

Action: Allow the print to cool completely on the bed before removal. Ensure your printing temperatures were within the optimal range throughout the entire print.

Optimizing Your Settings for Crack-Free PLA Prints

Fine-tuning your slicer settings is paramount. These adjustments directly influence how your PLA behaves during the printing process.

Key Slicer Settings to Check:

Printing Temperature: As mentioned, stay within the recommended 190-220°C range.
Bed Temperature: 50-60°C is generally sufficient for PLA.
Print Speed: Slower speeds, especially for the first layer (around 20-30 mm/s), improve adhesion.
Part Cooling Fan Speed: Start with the fan off for the first layer or two, then gradually increase to about 50-80% for subsequent layers.
Retraction Settings: Properly tuned retraction prevents stringing, which can sometimes interfere with layer adhesion.

Understanding Layer Adhesion

Good layer adhesion is the foundation of a strong PLA print. It occurs when the molten plastic from the current layer fuses effectively with the layer below it. When this fusion is weak, cracks can form between layers.

Temperature: Adequate nozzle temperature ensures the plastic is fluid enough to bond.
Cooling: Excessive cooling prevents proper fusion.
Print Speed: Printing too fast doesn’t give the layers enough time to bond.

Setting	Recommended Range for PLA	Impact on Cracking
Nozzle Temperature	190-220°C	Too low = poor adhesion; too high = degradation
Bed Temperature	50-60°C	Improves adhesion, reduces warping
Print Speed	40-80 mm/s	Slower speeds enhance layer bonding
Part Cooling Fan	50-80% (after first layers)	Too high = shrinkage/cracking; too low = sagging
First Layer Speed	20-30 mm/s	Crucial for strong bed adhesion