The first time I saw a 3D printer working on the internet, I thought to myself, “Wow, There’s a machine that gets my design and prints it!” After years of anticipation, I got my hands on an FDM 3D printer, and the problems came one after another. Blobs, zits, strings, cracks, and warping were the common ones. However, printing PETG and ABS were more challenging than the standard PLA filament. In this article, we will be covering the most effective ways to deal with the PETG blobbing. So:
What Are The Main Causes of PETG Blobbing?
Unwanted nozzle stops, back pressure, humidity, and dirty nozzles are the main reasons for PETG blobbing. Several methods like tuning print settings, drying filament, and cleaning nozzle can usually help you remove blobs. Yet, PETG blobbing may happen due to low-quality filament or environmental effects.
Several factors cause blobs, and many procedures can be done to get rid of them. Hence it’s best to follow a systematic approach, so here we go:
Clean The Nozzle
Before changing any parameters or materials, you should first check out the nozzle. Hot molten PETG is a sticky substance by nature, so small particles such as dirt can hook and draw it out of the nozzle.
If the melted PETG comes out when it shouldn’t, blobs and zits will grow on external walls.
You can use a brush or cotton cloth to clean the nozzle, be careful not to damage the nozzle’s hole, though. A slight deformity on the tip can change its behavior!
It’s good to know that some extruders come with temperature-resistant caps which prevent dust from disturbing the nozzle’s performance.
Sometimes a little bit of cleaning is all you need to do, yet PETG blobbing may have other reasons.
Calibrate Feed Rate
Every extruder movement is either done to lay melted filament on the surface or move to another location. There are situations that extruders should stop feeding when in the move. For example, printing two separate objects close to each other requires lots of displacement between the two. In this case, filament shouldn’t get out of the nozzle when in movement.
On the other hand, excess feed rate when the filament is getting consumed can produce blobs. The reason is that the extra melted filament has nowhere to go, so it adds up and forms zits. Now that we know the reasons behind this, it’s calibration time!
To calibrate your 3D printer, you need to have a caliper, marker, and a computer with slicer software installed on it.
The first step is to heat the nozzle to the printing temperature you are using and load the filament if it already hasn’t been loaded. In our case, PETG usually requires a nozzle temperature between 230 – 250oC.
Connect the 3D printer to your computer and use a slicer capable of sending single line G-codes. Now we can activate extruder relative movement by sending an M83 command to the machine. Details of sending commands are different among various slicers though they aren’t difficult to figure out.
The idea here is to command the printer to extrude 100mm of filament then check if it consumed 100mm. Otherwise, it needs calibration. To do so, use your marker and caliper and mark the filament exactly 150mm before the extruder’s entrance.
The next step is to send the command of G1 E100 F100 and wait until extrusion stops. Once it’s finished, measure the marked point’s distance from the extruder entrance. If it is 50mm, you’re good to go, But any different result makes calibration necessary. In PETG blobbing, the second measured length is below 50mm, and over-extrusion is happening. It would help if you calculated the stepper step/mm ratio.
Use the M503 command to get information through serial communication and read the E value in the M92 line. It’s the current step/mm value. Use the formula below to calculate the correct step/mm ratio:
(correct step/mm) = ( 100 × currrent step/mm ) / ( 150 – remaining fillament length in mm )
Now it’s time to set the correct step/mm in your 3D printer. To do that, you should send a command like M92 E[correct step/mm] and replace the value, then use M500 to save it.
It’s good to double-check if the extruder is consuming the right amount of filament with the caliper.
Find The Best Retraction Settings
Retracting filament back to the nozzle is another cool hack to prevent the melted plastic from flowing. However, be careful not to mess it up because adjusting the retraction setting can affect printing quality.
Different extruders may have different retraction settings. For example, Bowden drive extruders require more retraction distance due to their structure. On the other hand, direct-drive extruders put less tension on the filament string and require less displacement. A retraction of about seven millimeters for Bowden extruder and four millimeters for direct-drive systems can be a good starting point for your adjustments.
You can also change these retraction settings but be careful not to use high speeds; something around 20 to 25 mm/s is an acceptable value.
Hot melted PETG tends to flow and drop from the nozzle by nature. So excess print temperature can decrease its viscosity and result in severe filament oozing and PETG blobbing on external surfaces. As we mentioned earlier, most PETG filament brands have a printing temperature between 230 – 250oC.
It’s good to know that high printing temperatures can improve print strength. yet keep in mind that it also increases the chance of warping, bobbing, stringing, and other printing problems like the elephant foot.
Use Good Quality Filaments
In an ideal situation, 3D printer users only need to adjust filament feed rate, and the machine creates a uniform profile. Yet, real-world filaments don’t have constant diameters, and this characteristic can slightly alter your feed rate. Instant increase in feed rate is one of the main causes of PETG blobbing.
In this situation, all you can do is to buy high-quality products and hope for the best!
Dry The Filament
Polymers like Nylon and ABS tend to absorb water from their environment. If a wet filament goes to the nozzle, this excess humidity starts to boil and blobs and cracking noises appear; in lighter situations, it can decrease your overall print quality.
Unfortunately, PETG filaments also tend to absorb humidity, so there is a chance that moisture is the cause of your blobs.
There are ways to dry your filaments and many more to know about the situation. You can find the in depth instructions here.