Print gaps in layers are among the most common 3D printing defects. They occur for a variety of reasons, ranging from the slicer and printer choice to the user experience – and anything in-between.
The most common causes of 3D printing layer gaps are under-extrusion, an incorrectly set Z-offset, and poor quality filament. Of all, the harder to diagnose is under-extrusion, which can happen for a variety of reasons. First layer gaps can also occur due to incorrect bed leveling.
11 Reasons For Gaps In 3D Printed Layers
Gaps in 3D printing are one of the main causes of time and material loss. Finding out why they occur can help you correct these issues.
1. Clogs In Hot or Cold End
A frequent cause of gaps in printed layers is the presence of clogs in the extruder’s hot or cold end – depending on your printer model.
Clogs in the hot end are typically found in the nozzle. They can start as a small accumulation of material that is not cleaned promptly.
New filament clings to the clog and builds up, creating a partial blockage. Hence, the printer will extrude a smaller amount of material that will negatively impact adhesion.
In Bowden style printers, clogs are also common in the Bowden tube. Some printers are more prone to problems than others, the Ender 3 models being notorious for this issue.
2. Spool Knots
Spool knots can happen regardless of the filament you’re using and the printer you have, but are more common in soft filament types.
These kinks can prevent the extruder from pushing the filament into the hot end, or only a smaller quantity of filament might be fed.
The situation becomes similar to that of clogs, where the printer doesn’t feed sufficient material through the nozzle, leading to gaps in the nozzle.
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3. Low Print Temperature
Another culprit of inconsistent or under-extrusion is a too low print temperature.
There are various issues that could arise from a low temperature. On the one hand, the filament is harder to push through the nozzle. On the other hand, the layers won’t adhere to one another because the filament is not hot enough.
Depending on the actual temperature, you might end up with tiny holes in an otherwise decent model or a pile of loosely-joined threads.
4. Too Much Retraction
Correct printer calibration is key to successful 3D printing, and this is demonstrated by the retraction setting.
During non-extrusion movements, the printer pulls the filament higher up in the nozzle to prevent oozing.
If it pulls it too high up, it might not be able to push out a sufficient quantity of filament when extrusion movements resume. This usually leads to warping.
Alongside warping, too much retraction can also cause the same section of the filament thread to pass over the driver gear more than once.
The gear’s teeth can wear off the material, leading to filament stripping. Filament stripping is another cause of inconsistent extrusion and potential gaps in your layers.
5. Incorrect Filament Diameter
The first thing to learn when 3D printing is that the diameter of your filament must always match the settings in your slicer and the diameter of the nozzle.
If you’ve sliced the project for a lower size filament but switch to a larger diameter without reslicing – or if you pair a larger diameter filament with a smaller nozzle – the printer won’t be able to feed an adequate amount of it.
Like the factors above, this mistake leads to under-extrusion and can be the cause of gaps in your layers.
6. Fast Print Speed
If you’ve got the extrusion right but still end up with gaps, it might be worth it to investigate the feed rate and speed.
When you’re printing at a too fast speed, the extruded material doesn’t have the time to form a bond with the substrate (build plate or lower layer) before new filament is extruded.
Too fast printing can lead to a variety of issues ranging from layer separation to holes and gaps in the top layer.
7. Unleveled Bed
Gaps can happen at any moment during printing, including when printing the first layer of your project.
One reason for gaps in the first layer is an unlevel bed. If the nozzle gets too close to the build surface, it won’t have enough space to extrude filament properly. Your first layer may look wavy, or portions of it might miss completely.
An easy fix is to level the bed before each print.
8. Wrong Z-Offset
The other reason for gaps in the first layer is a wrong Z-offset. In this case, the nozzle gets too close to the build surface even if you’ve leveled the bed.
A low Z-offset appears as an improperly extruded line, whereas a high Z-offset can lead to problems like elephant foot and stringing.
9. Too Fast Cooling
If the printer extrudes sufficient filament, the bed is leveled, and the Z-offset is right, layer gaps can happen due to too fast cooling.
The cold air doesn’t give filament enough time to form a bond with the substrate, leading to layer separation. Delamination manifests as wavy gaps between the layers.
Complete layer separation could also occur, in which case your object will simply split into two or more parts.
10. Wet Filament
Beyond calibration problems, gaps can form when you’re printing with wet filament. That’s because the water inside the filament evaporates when the material passes through the hot end.
Vapors can sometimes get trapped in the material, so you’ll see air bubbles in the extruded filament.
These bubbles prevent proper adhesion and can lead to layer separation. This is why you should only print with dry filament.
11. Poor Filament Quality
Another filament-related problem involves the quality of the material. Poor quality filaments can trap moisture and dust faster than high-quality ones.
The thread diameter might also be inconsistent between various parts of the spool. All these issues can lead to print gaps in layers.
How To Fix Gaps In Layers
Knowing the reasons why layer gaps happen can help you pinpoint the cause. Once you do, follow the steps below to fix it.
1. Proper Printer Calibration
When it comes to it, the most common reasons for layer gaps are related to calibration. A few things to do include:
Raise hot end temperature
When setting the hot end temperature, it is often recommended to start from the lowest temperature for the material you’re printing with.
This prevents over-extrusion and an array of related issues. However, you should raise it in small increments at a time (around 5°C) until you get proper adhesion. Test the temperature with miniatures or small test prints.
Reduce retraction
Proper retraction is essential to avoid under-extrusion and prevent oozing. For most rigid filaments (PLA, ABS, PETG), a retraction between 0.5mm and 3mm should suffice.
You can adjust up to 4mm, but if you’re still experiencing oozing, you might be printing with poor quality filament or something else is wrong. Flexible filaments like TPU require a retraction distance up to 2mm, in general.
Abrasive and specialty filaments, such as PLA wood, typically require longer retractions up to 5mm to 7mm.
Reduce print speed
Another setting you should get right for quality prints is the print speed. A too low speed can lead to deformed layers.
A too high speed can lead to layer separation and gaps. Like the temperature and retraction, each material comes with a recommended print speed.
Start from one end of the range and decrease or increase in small increments at a time until you find the sweet spot for the specific filament you’re using.
Measure filament diameter
One important setting that even experienced users often overlook is the filament diameter. If it is too large for the nozzle – or different than the size input in the slicer – there might be gaps.
Always measure the filament diameter with a caliper and check the settings in your slicer. Adjust accordingly and slice again if necessary to ensure print quality.
Reduce fan speed
As explained, speedy cooling is a reason for layer separation. Hence, you should reduce the fan speed to the lowest possible setting for the material you’re using.
If the filament requires the fan to be 100%, make sure the room temperature is constant and above 77°C (but lower than 86°F) and that the printer is located away from open doors and windows.
Using an enclosure might help with particularly stubborn filaments like ABS – which is notorious for warping.
Adjust Z-offset
Lastly, make sure to adjust the Z-offset.
As a rule of thumb, the offset matches the filament diameter – another reason why measuring the filament with a caliper is crucial.
2. Bed Leveling
The simplest way to prevent adhesion issues and gaps in the first layers is to level the bed. You can do that manually:
- Clean the bed properly and wipe it with isopropyl alcohol.
- Preheat the bed and nozzle to the normal operating temperature for the material you want to print with.
- Home the printhead by taking it to the 0,0,0 position.
- Select Bed Leveling from your printer’s menu. This setting might have a different name on your hardware, such as Bad Tramming or Level Corners.
- Slide the printhead to one corner of the build plate and slip a piece of paper under it. Adjust the nozzle height until it barely touches the paper. Repeat for all corners and the center of the plate.
- Run a test and check if the first layer is printed properly.
3. Dry Filament Before Use
Another way to prevent layer separation and adhesion issues is by printing with dry filament. The simplest way to dry the material is with a filament dryer.
Alternatively, you can use the kitchen oven, a food dehydrator, the heated bed of the printer, and even the freezer for PETG.
4. Keep Nozzle Clean
Clogs and dirty nozzles can negatively impact your print, so keeping them clean is crucial. Wipe the part with a damp cloth after each use and remove filament residues with a wire brush.
If you’re dealing with stubborn clogs, a needle or solvent could help get rid of them.
5. Use Quality Filament
Lastly, don’t forget to check the quality of the filament you’re using.
Hatchbox, Prusament, and other big brand names are usually better bets than no-name materials.
Tips To Fill Layer Gaps In 3D Prints
If gaps happened but they are rather tiny, you might not have to discard the model.
Here’s how to fix it.
1. Use 3D Print Filler
3D print filler is a type of epoxy resin developed specifically for 3D printing filaments. It is generally compatible with all filament types and hardens quickly, allowing you to fill the gaps before finishing the project.
Simply follow the instructions on the filler’s label – these could vary from brand to brand. Use a spatula to apply resin to the gaps and smooth it as best as possible. Let it dry properly before continuing with post-processing.
2. Sand and Polish
If the gaps are few and superficial, you might not have to use a filler at all. Sand the entire surface with sandpaper, insisting on the spots where gaps occur.
Shave off sufficient material to mask the gap, then polish it with a paint product. Instead of polish, you could use colored paint.
3. Try Vapor Polishing
Vapor polishing is a chemical process achieved with acetone. The solvent doesn’t actually touch the surface, but you should place the object in a closed chamber or container where it can be surrounded by solvent vapors.
For a miniature, for instance, you should place a support inside a Tupperware and coat the container with paper towels soaked in 99% to 100% acetone (nail polish won’t work).
Place the item on the support and close the Tupperware with the lid. It can take several hours for the surface to smooth out, but this process can help get rid of superficial gaps and ridges or bumps.
4. Fill Gap in Cura
For gaps occurring between the walls or to filter out tiny gaps, you can use Cura’s fill gap setting. Slice the model again and start the print so that the printer can fill them.
Once done, sand and polish the model with your preferred method.
Final Thoughts
Layer gaps in 3D printing can happen for a variety of reasons, but more often than not, they are the result of improper calibration. Poor quality or wet filament can also impact the results, and sometimes, it could be a clog or other hardware glitch.
No matter what it is, we hope this guide can help you pinpoint and fix the issue.
