PETG is one of the most popular 3D printing filaments, but also one of the most challenging to work with. This material is highly hygroscopic and notorious for stringing and blobbing if you can’t manage to get the printing settings just right.
Typically, PETG stringing happens due to incorrect calibration, the use of wet filament, or poor quality material. Adjusting the nozzle temperature, retraction, print speed, travel speed, and cooling can help solve the problem. Enabling combing, coasting, and wiping are other ways to prevent PETG stringing and blobbing.
PETG printing issues can occur on all 3D printers, but the Ender 3 (Pro/V2) and Prusa printers are more likely to cause trouble.
Is PETG Supposed To Be Stringy?
PETG isn’t supposed to be stringy, but it often is because of its high extrusion temperature. This material has a high melting point and requires a nozzle temp between 210°C and 250°C.
When the nozzle temperature isn’t calibrated just right, though, the material could ooze. Oozing is a common cause of stringing, as is too slow cooling.
An incorrect retraction distance can also lead to stringing, as the melted filament in the nozzle sticks to the print.
PETG stringing on Ender 3 Pro or V2 can also happen due to an incorrect travel speed during non-extrusion movements. The same can lead to PETG stringing on Prusa Mini.
If you’ve never used PETG before, the only way to get settings just right is by trial and error.
Set up the printer according to the general recommendations in this article, then run a PETG stringing test to check the results. Fine-tune and adjust until your prints are perfect.
How To Prevent PETG From Stringing
PETG might be a difficult filament, but there are ways to avoid stringing and blobbing.
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The steps below should help you fix the issue.
1. Adjust Nozzle Temperature
The first thing to do if you notice stringing when printing with PETG is to adjust the nozzle temperature.
As mentioned above, this material requires temperatures between 210°C and 250°C. That’s a quite wide interval that gives enough room for fine-tuning but also for endless trials if you don’t know where to start.
An easy way to narrow down your options is to consider the type of printer you have.
Ender 3 users, for instance, might find that the perfect temperature interval for the Pro and V2 printers is between 220°C and 235°C. Prusa suggests a nozzle temperature of 230°C for the first layer and 240°C for all subsequent layers.
Most 3D printer brands provide similar recommendations, so you can simply check on the printer’s website or forums to find the right interval for your hardware.
2. Increase Retraction Speed
When printing with PETG, another factor that can lead to stringing is slow retraction.
When the extruder doesn’t retract the filament quickly enough during non-extrusion movements, the melted filament oozing from the nozzle can stick to the model and create hairline strings as the arm moves.
In this case, more important than the printer model is the type of extruder you have.
Bowden extruders require a retraction speed between 25 and 40 mm/second. The wide interval makes it possible to adjust the speed based on the project type and filament quality.
It is ideal to start from the lower threshold and increase the speed by 5 mm/s at a time, until stringing doesn’t occur anymore.
Direct drive extruders typically require a faster retraction speed of between 35 and 45 mm/second.
3. Increase Retraction Distance
If you’ve adjusted the retraction speed, but stringing still occurs, the next thing to check is the retraction distance.
This parameter defines how much filament is pulled back into the hot end at the end of an extrusion movement.
Once again, the type of extruder determines the optimal retraction distance.
In printers with a Bowden extruder, you should set the retraction distance between 6mm to 14mm. Direct drive printers require a shorter retraction, typically between 0.6mm and 2.8mm.
The actual distance is usually dictated by the printer brand, filament quality, and other printing parameters. For instance, most Ender 3 users may find that a retraction distance of 6mm suits them just fine.
To find the right setting for your machine, start from the lower number and increase by 0.5mm at a time until no stringing occurs.
4. Calibrate Print Speed
Print speed is another factor that influences PETG stringing, and you may find that this is one of the most temperamental filament types.
That’s because slower printing is typically needed to produce high-quality prints.
Yet, PETG oozing from the nozzle can easily stick to the model and result in stringing. Thus, you’ll have to find a compromise between print quality and fast printing.
According to Creality, you should set the print speed between 30 and 50 mm/second.
5. Increase Travel Speed
Travel speed is the speed at which the arm moves during non-extrusion. Once again, a higher velocity can prevent stringing by lowering the risk of oozing.
Similar to the printing speed, adjusting the travel speed for PETG can be challenging, since both slow and fast movements are bad.
The best thing to do is to work from the pre-set travel speed and increase by 5 to 10 mm/second at a time until no blobs have time to form on the hot end during non-extrusion movements.
6. Enable Combing
Combing is a function that alters the extruder’s pathway, so that the arm never has to cross large empty spaces. Through combing, you can minimize travel distance, which is another secret to preventing PETG stringing.
Enabling the combing mode is straightforward in Cura. The setting is found in the Travel menu just beneath the Retraction category.
Tick the box next to it to enable the mode, and your slicer will take care of everything else for you.
Alternatively, you might be able to enable combing directly from the G-code. This function may be found under different names in slicing programs other than Cura.
7. Enable Coasting
Coasting is another method to prevent oozing during non-extrusion movements, but this time the slicer commands the printer to turn off the extruder motor a few seconds before extrusion is stopped.
In this way, the extruder uses the portion of melted filament in the hot end, and no other filament is pushed down until extrusion resumes.
The downside is that, even if costing solves stringing problems, it often results in an under-extrusion line that can affect the quality of your model.
For this reason, coasting is generally only used when stringing is severe.
If you do want to use coasting, you can find the setting in Cura’s experimental section. Tick the box next to Enable Coasting and you’re good to go.
8. Enable Wiping
Like combing and coasting, wiping is a function developed to prevent blobbing and stringing.
However, instead of altering the non-extrusion movements or stopping the motor, the printer “wipes” the nozzle on the last layer before moving the arm to the new extrusion spot.
The nozzle is cleansed of excess material, which is spread over the last row. This solves stringing, but it could smear out the outside wall of your model.
That said, you can enable wiping in Cura from the Walls section in the Expert menu under Print Settings.
9. Adjust Z-Hop Height
Z-hop is a function developed to raise the nozzle higher during retraction (or lower the bed to obtain the same effect).
Its role is to put more distance between the nozzle and the model, to prevent the hot end from bumping into printed parts when moving from one extrusion point to another.
When printing with PETG, a higher Z-hop can prevent the filament blobs from sticking to the last row, reducing stringing.
By default, Cura sets the Z-hop height to 0.2mm, which is the default thickness of layers printed with a 0.4mm nozzle. To prevent stringing, adjust the Z-hop height to at least 0.4mm.
10. Adjust Layer Height
Another thing to adjust when printing with PETG is the layer height (or thickness).
This material doesn’t require any squishing to stick to the bed or for the rows to stick to one another, so you should start with an initial layer height of 0.28mm and work your way from there.
11. Calibrate Fan Speed
A common advice when printing with PETG is to keep the fan speed at 100% at all times.
However, if fast cooling prevents stringing, it can also lead to delamination if the filament is not completely dry – which is much more common than you think, considering its hygroscopic nature.
For this reason, you should turn off the cooling fan for the first few rows, then turn it to 100%. If you’re suspecting the filament is wet, reducing the fan at 50% might help increase print quality.
12. Change Infill Pattern
While not many think of it, the type of infill pattern you’re using can also make or break the deal.
Patterns that require a great deal of non-extrusion movements are the worst, as stringing is more likely to occur – and it could affect the model’s exterior, too.
One of the best infill patterns for PETG is zig-zag, which consists of a continuous line from one end to another. This is also one of the fastest infill patterns, so it’s a win-win.
13. Use High-Quality PETG
Beyond printer and slicer settings, a factor that affects stringing is the quality of the filament. You should always use high-quality materials from known brands.
While these options are more expensive, they’ll save you time, as well as your sanity.
14. Keep Filament Dry
Filament quality aside, you should also make sure the filament is stored properly and preferably in filament boxes.
If you don’t have a filament box and don’t feel like buying one, at least keep the spool in a sealed bag with a few packets of silica gel to absorb moisture.
Before printing, you should also dry PETG in a filament dryer, kitchen oven, or food dehydrator.
PETG Stringing vs. Oozing
Stringing and oozing are often related, but they are two different issues. Let’s find out the differences.
PETG Stringing
PETG stringing is a phenomenon that happens when filament oozing from the nozzle sticks to an already printed part and travels between two parts, creating annoying “hairs.”
This defect can affect the visual value of your printed part and even interfere with its functional role. Moreover, stringing consumes more material.
PETG Oozing
Oozing refers to melted filament coming out of the nozzle during non-extrusion movements. It is a common phenomenon for PETG, which is a material with a high melting point.
However, oozing doesn’t necessarily translate into stringing. The material blob can also result in zits and other printing defects.
With the right settings, stringing and zits can be prevented even if blobs of filament form on the nozzle during non-extrusion.
Frequently Asked Questions
Does PETG string more than PLA?
Yes, PETG strings much more than PLA.
It is also more common to create other printing defects, including elephant foot, blobs, and other over-extrusion defects.
Should I use combing with PETG?
Yes. Combing is one of the best ways to prevent stringing, and the function is easy to enable in the slicer.
Final Thoughts
PETG is a difficult material that can give a variety of printing defects. Stringing is one of the most common, caused by blobs of molten material that stick to the printed parts and create “hairs” on the print.
Proper printer calibration, enabling combing, wiping, and coasting, changing the infill pattern, and using dry, quality filament, are a few ways to get rid of this issue.
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