One of the most frustrating aspects of 3d printing is printing defects. We’ve all been there. You’ve got a great design. You’ve sliced it and everything looks good. You start the job, excited to see the results – except the results aren’t so exciting.
Your object didn’t print out the way you thought it would. You’re out the time you spent printing, the material you used to print and all you’re left with are less than stellar results and a feeling of frustration at the whole process.
The good news is that most printing defects are easily solvable once you know where to look and what to do. In this article we’re going to look at three of the most common printing problems – pillowing, stringing and splitting. We’ll talk about what they are, why they occur and the steps that you can take to prevent them from ever happening again.
Image of pillowing, courtesy of Ultimaker's blog
Pillowing occurs on the top surface of an object. It looks like there are gaps in the surface layer, along with little bumps or pillows.
What causes Pillowing?
In general, pillowing is caused by a top layer that is too thin and/or improper cooling of that layer. Under certain circumstances, insufficient infill can also contribute to the problem. Let’s take a look at what you can do to prevent pillowing from happening.
Increase the Thickness of the Top Layer
The easiest way to prevent pillowing is to increase the thickness of the top layer of your object. In most slicer applications, this can be done by going to the advanced settings tab and looking for “Bottom/Top Thickness”. In most cases you want to have a top layer that is at least 6 layers thick.
This means that if you are printing with a 0.1 mm layer height, you want to set your Bottom/Top Thickness to 0.6 mm. If this doesn’t solve the problem, you can increase the Bottom/Top Thickness setting to 0.8 mm. In general, the thinner your layer height, the more top layers you’re going to need to sufficiently cover the infill on your object.
On the subject of infill, the less you have the more difficult it becomes to lay down a top layer. While not a direct cause of pillowing, insufficient infill can contribute to the problem by causing your top player to droop and sag, especially when you add in additional layers. Therefore, it is always a good idea to slightly increase your infill percentage when attempting to prevent pillowing from occurring.
When you’re printing the top layer of your object, it’s very important that you are cooling the print material properly. If the top layer takes too long to cool, it may sag in between the infill layers and curl up where it touches the infill layers. This is especially true when you are using a thin layer height. The result is an uneven surface that becomes bumpy and uneven as the top layers are added.
Make sure that your cooling fans are operating correctly both prior to printing and as the top layer of your object is being laid down. Make sure that the fans are pointed in the right direction and are circulating air in the direction of the object that you are printing.
Perhaps the worst case of stringing we've seen, image courtesy of Zheng3's blog
Sometimes your object will have thin strands of material where no printing should be occurring, usually across spaces where the print head has traveled from one printing point to another. This problem is known as stringing and it can be one of the most annoying defects to deal with.
What causes Stringing?
Stringing is usually caused by the print nozzle oozing print material as it moves from one place to another. The oozed material cools and hardens into thin “strings” – hence the name. Let’s take a look at a couple of adjustments that you can make to combat stringing.
Retraction is a slicer setting that is usually activated by default. When retraction is activated, the printing filament is pulled back or retracted into the print head any time the head moves from one print point to another. So, if you’re seeing stringing on your objects, the first thing to do is to check that the retraction setting is indeed active.
If retraction is activated and stringing is still occurring, you can then use the additional settings tab to incrementally increase retraction distance and speed. This will cause the filament to retract farther into the print head more quickly.
A common cause of persistent stringing is a print temperature that is too high. When the temperature in the print head is too high for the material being used, the filament becomes too viscous and watery and leaks out the print nozzle. If you’re still experiencing stringing after checking your retraction settings, try reducing your print temperature in 5C increments to see if that clears up the problem.
If you have lowered your print temperature to prevent stringing, you will also likely need to reduce your print speed to prevent potential problems from under extrusion from occurring. A lower print temperature means that the print material will flow more slowly. Keeping the print speed where it was can mean that gaps and holes can begin to appear in your object in the places where the extruded material couldn’t keep up with the speed of the print head.
Splitting / Cracking
Sometimes a print job will be progressing nicely with no apparent problems. You leave the room, and when you come back you see that your object has developed a split or crack along one of its sides at a point where everything seemed fine before.
What causes Splitting or Cracking in my print?
As you know, your printer makes an object by laying down layers of print material, one on top of the other. It is imperative that each new layer binds to the previous one.
Splitting occurs when one layer bonds inadequately with another layer. When this happens, as the object cools, a split or crack occurs between the two inadequately bonded layers. Luckily there are a couple of things that you can do to prevent splitting from occurring.
Decrease Layer Height
In order for two layers of print material to bond, the print nozzle needs to apply exactly the right amount of pressure to the layer currently being laid down. Too much pressure and the layer will move off to one side or smear. Too little pressure and the layer can’t adequately meld to the previous print layer. The result is a crack.
In order to make sure that the print nozzle is applying adequate pressure, make sure that your layer height is about 20% smaller than your print nozzle diameter. That ratio insures that the nozzle is pressing down enough on the material being extruded to adequately bond it to the previous layer.
Increase Print Temperature
If your material is being extruded at too cool of a temperature, it cannot easily bond with the material that’s already been laid down. Therefore, as it cools, it will shrink and pull away from the layer below it. The result is a split or crack.
To avoid this from happening, increase you print temperature slightly. The slightly higher temperature will insure that the extruded layer bonds with the previous layer so that both layers essentially cool as one object, thus avoiding the splitting that would otherwise occur.
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