Prevent PETG Blobbing. Detailed 3D Printing Guide!

by Mike Brooks | Last Updated: March 5, 2022

3D printing professionals and hobbyists look forward to printing excellent objects designed in the printer software.

However, the 3D printing process is a complex one. Achieving high-class results depend on getting it suitable with all parts of the process.

Significantly, printer parts, software, and files must all work well; otherwise, any failure from any of these components results in low print quality.

One manifestation of poor quality print is the appearance of blobs and stringing in 3D printed objects.

What is a PETG blobbing or stringing? A blob or stringing in 3D printing refers to small lumps or hangings seen on the surface of a 3D final product.

It happens when a layered print finishes on the build plate, yet the filament is still under pressure in the print head. It results in a burst of over extrusion that can occur at the start or within a print layer.

It would help prevent blobs and stringings to ensure 3D print products have an excellent finish surface. The article, well researched, serves as a guide to avoiding PETG blobs in 3D printing.

Main Causes of PETG Blobbing

PETG is an abbreviation of Polyethylene terephthalate. It improves PET with the additional “G” representing glycol. Glycol stands for the molecular property that gives PETG a shiny glass-like surface on objects.

Blobs are a common problem with PETG filaments. Still, blobs happen when you get your printer settings and configuration values wrong.

The common issues that result in blobs and stringings in PETG plastics:

Excessive Printing Temperature

PETG prints at a heated bed temperature of 220-265 degrees Celsius. Also, some printer hot ends fitted with PTFE tubes are a common feature in 3D printers using PETG filament.

Meaning if you print with temperatures above the stipulated hardware requirements, you will experience blobs in your 3D prints.

Alternating Printing Speeds

The nozzle printing speed affects direct-drive extruders. If your printing speed keeps alternating, the print layers on the heated bed will finish before the hot end extrudes subsequent filament causing stringings.

Over Extrusion

Over extrusion is a common cause of blobs. Whenever molten plastic extrudes on your first layer, it causes eventual stringing. The fast rate of filament extrusion does not allow for the layers to take their designated shape, and as a result, it blobs.

Improper Extruder Pathing

Your 3D printer nozzle follows a specific path to print. When printing, the nozzle extrudes molten filament following this predetermined path as stipulated by the print settings.

The print blobs appear whenever the print nozzle deviates from the path because of wrong settings or printer mechanical parts malfunction.

How Do I Stop PETG Blobbing?

Some of the leading causes of PETG blobs include:

• Unlimited nozzle stops
• Backpressure
• Humidity
• Dirty nozzle

Therefore, if you want to stop PETG filament blobs, you need to:

Adjust Printing Temperature

Naturally, melted PETG filament freely flows from the print nozzle. Thus, the excess temperature can worsen by causing severe oozing and PETG blobs on the print part surface.

Many PETG plastics have print temperatures capped at 230-250 degrees Celsius. Remember, 3D printing at high temperatures improves the tensile strength of a 3D print.

However, it is the primary source of increased stringing in 3D printed objects.

Layer Adhesion

Proper layer adhesion on your build plate enables the first layer to stabilize on the same spot.

It also allows the printer nozzle that extrudes following a predetermined path to be effective as the initial layers of the object as the adhesion restricts in the same place.

Clean the Printer Nozzle

Often double-check and clean out your printer nozzle. Moreover, hot and molten PETG plastic is pretty sticky, so dirt particles can make it move out of the nozzle unexpectedly.

Anytime molten PETG plastic comes out of the nozzle before extrusion, it causes stringings and blobs. Therefore, it will be helpful if you clean the nozzle using a clean cotton cloth or a brush. Do it cautiously to avoid damaging the nozzle.

Get It Right With Retraction Settings

The capacity of the printer to retract filament back to the nozzle is vital as it prevents PETG filament from flowing. However, you need to be extra careful when adjusting the printer retraction settings.

Why? Because the retraction settings impact the final print quality.

Moreover, different extruders have different retraction settings, so you need to check out appropriate settings before making any adjustments.

How to Prevent PETG Blobs and Stringing

Extruding filaments in places you shouldn’t cause blobs on the print surface. However, it will depend on whether the printer extruder is moving or not. Over extrusion remains the most significant cause of most PETG stringings and blobs.

To prevent PETG blobs and stringings work on the following 3D printer settings:

• 3D printer retraction speed
• The nozzle retraction distance
• 3D printer nozzle temperature
• The 3D printing speed
• Configuration of travel speed

Effective Ways to Get Rid of PETG Blobbing

Stringings and blobs are the causes of unsightly final print surface appearance. For this reason, you need to do everything to eliminate the problem.

Use Dry Filaments

PETG Filament tends to absorb water, and the moisture is not suitable for 3D printing. Always dry your PETG plastic before printing. Moist filaments cause oozing and stringings that make for poor-quality final prints.

Additionally, wet filament causes cracking sounds during printing and causes weak layer adhesion.

Calibrate Feed Rate

Consider a situation when you are printing two separate objects close to each other in the build plate. You need to calibrate the extruder feed rate as the extruder will need to stop extruding molten filament on movement between the two objects.

If the feed rate settings are wrong, excess feed rate will cause stringings as the extruder will extrude filament even in the space between the objects.

Use Good Quality Filament

Filaments may differ in diameter size. It’s a quality that can significantly change your feed rate. You need to use a high-quality filament to avoid blobs on print surfaces.

Also, an abrupt increase in feed rate is a vital cause of blobs and stringings; Only good quality filament will help you avoid this problem.

Does PETG Need More Retraction?

PETG filament doesn’t need a high retraction speed. It thrives in low retraction speed.

Therefore, if you set your PETG retraction speed and find that at that value, it still causes blobs, keeps reducing it, and stringing will stop.

Notably, the ideal PETG retraction speed is 25mm per second.

Conclusion

Every 3D printer user’s dream is to create a high-quality print with a highly pleasing appearance. It’s an achievable dream that many 3D hobbyists readily achieve.

However, the 3D printing process faces numerous challenges as the printer’s mechanical parts, software, files, and filaments must all work efficiently.

Otherwise, challenges such as PETG blobs and stringings occur due to malfunction extruders or wrong printer settings.

This article guides you skillfully on preventing PETG 3D printing blobs and stringings for better print quality.

Michael Brooks is the founder of M3DZone.com. He sees a very bright future for 3D printing that's why his mission is to try and make this easy for everyone. Discover your hidden talent and creativity. You can follow here: Facebook, Twitter & Pinterest.