3D printing is a rather intricate process as it requires a long list of parts to work as intended to produce a good result. The mechanical parts of the 3D printer, the filament, the printer software, and the printer files all have a significant role, and even if just one of them fails, the result is often not satisfying.
Due to the long list of things that can go wrong, imperfections in the final product can be disappointing, mainly because the problem will keep happening until you find a way to fix it.
One of such problems is the appearance of blobs and stringing on your print, which is especially common with PETG filaments. As these blobs and strings can easily ruin the look of your 3D prints, it’s a problem that you can’t ignore.
So, how can you prevent PETG blobs and stringing?
As PETG blobs and stringing are often related to the settings of your 3D printer, configuring your printer with the correct values will prevent these issues from happening again.
Below are the printer settings you can configure, alongside some experimental features you can use as a last resort.
- Retraction speed
- Retraction distance
- Retraction minimum travel
- Travel speed
- Nozzle temperature
- Print speed
Optimizing these settings can be challenging due to both the knowledge and the amount of trial and error needed to get right, especially if you are new in the 3D printing space.
In the next section, we will be going into detail about each of these settings and share tips and tricks that will make it much easier for you to configure your printer in a way where PETG blobs and stringing won’t trouble you anymore.
Preventing PETG Blobs and Stringing
When the 3D printer extrudes filaments in areas where it shouldn’t, blobs and stringing occur depending on whether the extruder is moving or not.
Even though blobs and stringing look different from the outside, they are caused by the shared problem of over-extrusion. So, if you solve the over-extrusion problem, you would be preventing both blobs and stringing from troubling you again.
As over-extrusion is usually caused by incorrect printer configuration, you will need to correct these settings to solve the issue.
Without further ado, let’s get into the settings.
The retraction speed setting configures how quickly the extruder retracts the filament.
When the retraction speed is too low, the extruder takes a long time to retract the filament back in, which often causes over-extrusion as the filament keeps coming out of the nozzle before the extruder can fully retract it.
On the other hand, a retraction speed that is too high will cause the extruder to retract the filament way too much, producing a long period of delay where the extruder will have to wait for the filament to come back down.
A low retraction speed is one of the primary causes of PETG blobs and stringing, as it directly causes over-extrusion by causing the filament to stay on the nozzle when it shouldn’t.
While the exact location depends on your slicer, you can most likely find the retraction speed setting in the menu that contains retraction settings.
To correct the retraction speed setting, you can start by increasing the retraction speed by increments of 5 millimeters/second. If adjusting the retraction speed made the situation better, you can use smaller increments for fine-tuning.
As the optimal retraction speed changes from printer to printer, the configuration requires trial and error.
Bonus Tip: Bowden extruders often require higher retraction speeds compared to direct drive extruders, so feel free to start increasing the retraction speed in larger increments to see quicker results.
The retraction distance setting configures how far back the extruder retracts the filament.
When the retraction distance is too low, the filament stays very close to the tip of the nozzle after retraction. As you may expect, this can cause over-extrusion due to the filament being in a spot where it can easily come out of the nozzle.
On the other hand, if you set the retraction distance to a number that is too high, you will experience extended delays after each retraction as the filament will have to come back down to the nozzle. In some cases, a retraction distance that is too high can even cause the extruder to clog.
Just as low retraction speed, low retraction distance is one of the most common reasons behind PETG oozing and stringing.
Even if the retraction speed is optimal, a low retraction distance can easily cause over-extrusion as the filament would have nowhere to go.
You should be able to find the retraction distance setting in the retraction settings of your slicer. If you have already found the retraction speed setting, there is a good chance that this setting is right next to it.
To correct the retraction distance setting, start increasing retraction distance by increments of 1 millimeter. Just as you have done with the retraction speed setting, you can fine-tune with smaller increments after seeing improvements.
While the correct retraction distance depends on your printer, the physical length of the nozzle can serve as a maximum length for this setting.
For instance, if the length of the nozzle is 12mm, setting the retraction distance to anything higher can cause delays and clogging issues.
Retraction Minimum Travel
The retraction minimum travel setting configures the minimum extruder travel distance required to trigger retraction.
When the retraction minimum travel setting is set to a number that is too high, retraction may never take place depending on the model you are printing. As a result, the filament always stays at the tip of the nozzle, which may lead to over-extrusion.
On the other hand, if you set the retraction minimum travel setting to a number that is too low, you may experience filament grinding due to back-to-back retractions all the time.
While a high retraction minimum travel value is recommended to prevent the risk of filament grinding (which can cause the print to fail), reducing it for models where the travel distances are too low can be quite helpful to prevent PETG blobs and stringing.
As the paths your extruder takes are highly dependent on the model you print, the best course of action is to adjust this setting on a print-by-print basis.
The retraction minimum travel setting is located in the retraction settings of your slicer alongside retraction speed and retraction distance.
To correct the retraction minimum travel setting, start increasing the retraction minimum travel value by increments of 5 millimeters.
Set the retraction minimum travel setting to the highest possible value where you don’t experience blobs and stringing to lower the risk of filament grinding.
Test prints are especially useful for configuring this setting due to the setting’s dependency on the model you are printing.
The travel speed setting configures how quickly the extruder moves between points while not extruding the filament.
A low travel speed setting causes the extruder to move way too slowly between points, which may cause the PETG on the tip of the nozzle to ooze, causing blobs and stringing.
On the other hand, setting the travel speed to a value that is too high can cause problems such as ghosting (also known as ringing, rippling, or echoing), where artifacts start appearing on your print.
As a low travel speed can cause blobs and stringing, and a high travel speed can cause ghosting, it’s significant to find a balanced value where you won’t be facing either of these issues.
The travel speed setting is usually located in the speed settings of your slicer alongside other speed-related settings such as print speed, which should be fairly easy to find.
To correct the travel speed setting, increase the travel speed value by increments of 5-10 millimeters/second until you find a balanced value where you don’t experience any blobs, stringing, or ghosting.
As finding the optimal value can take a few tries, test prints can once again be helpful to see the differences between different speeds.
The nozzle temperature setting configures the temperature the filament is heated to by the printer.
A nozzle temperature value that is too high can cause the filament to be heated way too much, which results in it melting faster than it should. When the filament gets over-melted, it starts flowing out of the extruder uncontrollably, which can cause blobs and stringing.
On the flip side, a nozzle temperature value that is too low won’t melt the filament as intended. Filament that hasn’t melted enough won’t flow from the nozzle, causing print faults.
As the melting point of a filament depends on the material it’s made of and its brand, you will need to set the nozzle temperature to a level that works for the filament you use.
While a nozzle temperature range of 230 degrees Celsius to 260 degrees Celsius is recommended for PETG filament, you can often find the exact temperature suggested by the filament manufacturer on the packaging.
Nozzle temperature is also called printing temperature by some slicers, so make sure to look for both of these alternatives to find this setting. For instance, in Cura, you will find this setting under the material section with the name printing temperature.
To correct the nozzle temperature setting, input the temperature that the manufacturer of your filament recommends.
If there is no recommended temperature, try testing different temperatures between 230 and 260 degrees Celsius by 5-degree increments until you get the desired results.
As filaments of the same material can also show a difference in melting temperature, it’s a good idea to double-check this setting whenever you buy a new spool of filament, especially if it’s a different brand.
The print speed setting configures the overall speed the printer moves at while it’s printing your model.
If the print speed is set to a value that is too low, blobs may occur as a result of the nozzle staying in the same place while the filament keeps melting.
On the other hand, a high print speed usually causes under-extrusion due to the filament not having enough time to melt. Alongside under-extrusion, you may face issues such as weak layer adhesion, ghosting (ringing), and misaligned layers with print speeds that are too high.
You can find the print speed setting in the speed section of your slicer, along with other print speed-related settings such as infill speed, wall speed, and top/bottom speeds.
To correct the print speed setting, increase the print speed value by increments of 5-10 millimeters/second until you push it to the highest value where you don’t experience any problems.
We highly recommend configuring the settings listed above (especially the ones that are retraction-related) in the best way you can before moving on to the experimental features we will be talking about next, as these features are meant to be used as a last-ditch effort most of the time.
Coasting is an experimental feature that is found in some slicers such as Cura.
When enabled, the coasting feature replaces the last few millimeters of extrusion with a travel move where the printer stops extruding. As a result, the chance of blobs and stringing is reduced.
If you are still having problems with PETG blobs and stringing after configuring all of the other settings, enabling coasting may be able to fix the problem.
As too much coasting can cause under-extrusion problems, you may need to tinker with coasting-related parameters such as coasting volume and coasting speed to get the maximum efficiency from this feature.
While coasting speed often doesn’t need too much adjustment, you can configure the coasting volume by increments of 0.01 cubic millimeters until you get the desired results.
Wiping is another optional, experimental feature that you can find in some slicers such as Cura.
When enabled, the wiping feature causes the nozzle to move over the outer layer of the model to wipe any remaining filament off. As a result, the nozzle is free of any leftover filament that may cause blobs or stringing.
Enabling wiping can be a very simple way of preventing blobs and stringing, especially when you use it in conjunction with coasting.
Similar to coasting, the wiping feature also has a parameter you can adjust, called wipe distance. You can configure this value by increments of 0.01 millimeters until you get the desired results.
Combing (Travel Path Adjustment)
The paths generated by your slicer that your extruder will follow while printing a model are called travel paths.
As travel paths where the extruder has to move over empty areas can cause stringing (even though they shouldn’t with the correct settings), a last-resort solution is to adjust the travel paths in a way where the extruder never leaves the boundaries of the print.
You can find a feature called combing in some slicers and enabling it causes the travel paths to be re-calculated in a way where the extruder always stays over the print, even if it means that the travel distances will be greater.
If you are using Cura, you can find the combing setting in the Travel menu of your slicer.
Keeping the travel paths on the boundaries of the print reduces the need for retraction and can help prevent the filament from stringing.
Vertical Lift (Z-Hop)
Vertical lift (z-hop) is a feature that causes the nozzle to move up by a slight margin (or causes the plate to move down) after a retraction.
When enabled, this feature can help prevent PETG from blobbing as the extruder won’t be able to leave leftover filament on the print due to the distance created.
If you are using Cura, you can find the Z-hop setting with the label “Z-hop when retracted” in the Travel menu.
That being said, there are a lot of mixed opinions about this setting in the 3D printing community, as some people have reported that it actually made the stringing and the blobbing issues even worse.
As a result, we recommend experimenting with this feature only if nothing else has solved your problems with blobs or stringing.
Can Moisture Cause Blobs and Stringing?
If configuring all of the settings we have listed above wasn’t enough to prevent your PETG filament from stringing and blobbing, the problem may be related to the filament itself.
Moisture can cause the filament to blob and string, and it usually brings other issues such as cracking sounds, weak layer adhesion, uneven extrusion, and fuzzy surfaces on the prints.
As it’s almost impossible to understand if the filament is moist just by looking at it, the symptoms that arise during printing are pretty much the only time where you will be to tell that moisture has indeed made its way into your filament.
If you think that your filament has been exposed to moisture, you will need to dry it before you use it again.
While experiencing blobbing and stringing with your PETG filament can certainly be a nightmare, correctly configuring your printer solves these issues more often than not.
Even though configuring these settings can take a significant amount of time (especially if it’s your first time), there isn’t a whole lot of technical complexity associated with the process, leaving it down to patience for the most part.
Remember that troubleshooting is a vital part of 3D printing, and think of resolving these issues as a learning experience that allowed you to be more knowledgeable about configuring your printer.