Advanced guide to printing PETG Filament

Author: Matt Tyson/Monday, 20 May 2019/Categories: How To

Advanced guide to printing PETG Filament

Combining excellent printability and balanced mechanical properties, PETG is a popular material due to its improved mechanical and thermal properties when compared to regular PLA.

Contents:

What is PET / PETG?
  PETG
  Nano-reinforced PETG

Printing Requirements
  Recommendations

Printer Setup
  Loading & Unloading Filament
  Bed and Printing Surface
  Bed Leveling & Nozzle Height
  Enclosure
  Filament Storage

Printer Settings
  Nozzle Temperature
  Bed Temperature
  Pre-heating
  Enclosure Temperature
  Cooling
  Rafts
  Supports

Post Printing
  Removing a print after completion
  Removing Layer Lines
  Painting
  Joining

Trouble Shooting
  Blocked Nozzle / Filament Jam
  Heat Creep
  Stringing / Oozing
  Warping
  Poor Layer Adhesion
  Difficult to remove prints


What is PETG?


PETG

PETG is a glycol-modified variant of PET (Polyethylene Terephthalate) and the most popular material in the PET family of plastics. The glycol in PETG offers improved printability and toughness compared to other PET copolyesters making it the most suitable variant for 3D printing. Due to the benefits and popularity of PETG, it is uncommon to print pure PET filaments.

Compared to regular PLA, PETG offers improved mechanical and thermal properties while maintaining excellent printability and reliability. Although not a direct replacement for ABS, PETG is a great choice for users who experience difficulty printing ABS due to warping or cracking and require improved mechanical properties to PLA with excellent dimensional stability.

PETG exhibits a low chemical resistance and moderate temperature resistance, softening at 80°C (Glass Transition and Vicat temperature).

Nano-reinforced PETG (PolyMax™)

PolyMax™ PETG is a nano-reinforced PETG material exhibiting superior impact resistance and ductility when compared with regular PETG, PLA and ABS filaments. Combining superior performance and printability, PolyMax™ PETG is an excellent material for a wide range of functional applications requiring durability, ductility, stiffness and near-zero warping on a wide range of printers.

PolyMax™ PETG exhibits the same chemical resistance and temperature resistance as quality PETG filaments.

Recommended settings are the same as regular PETG and we use the same settings for both PolyMax PETG and regular PETG.


printing requirements 


Recommendations

Before we start lets double check your printer is capable of printing PETG, of course this is only a brief run down.

Material: We recommend only printing with a quality PETG filament.

Minimum Extruder Temperature: 230°C minimum is recommended (This of course can vary on brand)

Heated Bed: Yes, 70°C minimum is recommended.

Part Cooling Fan: The ability to control the cooling fan is recommended.

Enclosure: PETG has great dimensional stability but an enclosure will certainly help when printing larger parts.

Feeding / Spooling: No specific requirements. 

Other Notes: N/A


Printer Setup


Loading and Unloading Filament

Changing between two PETG materials:
If the printer is currently loaded with a different PETG material, unload that material at 230-240°C and extrude your PETG filament at the same temperature. Stop extruding the PETG filament after the previous colour is completely purged.

Changing from a higher temperature material:
If the printer is currently loaded with a higher temperature material (for example ABS), unload that material at its recommended printing temperature, and then load and extrude your PETG filament at that same higher temperature. It is important to load the PETG at this higher temperature so the previous material can be pushed out. Stop extruding the PETG filament after the previous material has been completely purged.

Changing from a lower temperature material:
If the printer is currently loaded with a different lower temperature material, unload that material at its recommended printing temperature, and then load and extrude your PETG filament at 230-240°C. Stop extruding the PETG filament after the previous material has been completely purged.

Bed and Printing Surface

For PETG printing there are a variety of optimal print surfaces but with some surfaces there are some important details to take note of.

Glass Bed (with glue)
Many users print PETG straight onto a heated glass bed. We recommend applying a layer of glue stick which acts as a ‘release agent’ when removing the finished print.

Printing PETG straight onto glass can chip or break the glass build plate.

Printing PETG on glass with glue stick gives the bottom of your prints an incredibly smooth and shiny finish.

Once the 3D Print is completed, it must be removed from the build plate when the temperature is high. Removing a print after the bed has cooled may cause the glass to break because the print may shrink more rapidly than the glass plate.

Printing Sheets (Buildtak, FlashForge etc.)

These surfaces are an adhesive backed sheet designed to stick onto your printers bed or removable platform. These sheets are great when printing PETG due to their compatibility with other 3D printing materials.

In our experience we have found the FlashForge sheets are better than BuildTak™ for PETG printing as the sheets are more durable and the adhesive helps to prevent the sheets lifting when the heated bed is set for PETG temperatures.

It is possible to slice or damage these sheets however if you remove the parts gently and set your nozzle height correctly, these sheets can last longer than other surfaces.

Perforated / Textured Boards
Some printers are designed with a perforated or textured bed. During printing, the extruded PETG plastic sticks through the perforated holes, gripping the plastic to the board. 3D Printing on perforated boards will require a raft to ensure the final part has a smooth bottom surface.

Success with perforated beds and PETG will depend on the plastic the perforated board is manufactured with.

Bed Leveling & Nozzle Height

It is important when printing PETG that your first layer adheres to the printing bed. To achieve this you must ensure your bed is perfectly leveled and your nozzle height is set correctly.

Since PETG will require a heated bed when printing, preheat the heated bed (70 - 80°C) before calibrating your nozzle height or leveling 

The ideal nozzle height when printing most materials (including PETG) is a distance of 0.1mm, this is the thickness of two pieces of paper. When changing between bed surfaces, it is important to adjust the nozzle height again to compensate for the added thickness of the bed surface.

Enclosure

An enclosure is not required when printing PETG.

Printing PETG on an enclosed printer can still be beneficial as the enclosure protects the print from drafts and external temperature changes, important when printing large parts.

Filament Storage

Like many other plastics, PETG is a hygroscopic material, absorbing moisture from its surrounding environment. When the filament passes through the hot end the moisture rapidly expands creating bubbles in between layers, poor layer adhesion, inconsistent extrusion due to material expansion and thus poor surface quality.

PETG will typically absorb moisture over a period of months however in environments with high humidity (evaporative air-conditioning) this process can take days.

Preventing Moisture Absorption:
It is important to store and print your PETG materials in their optimum environment (below 20% humidity) to prevent moisture absorption, as excessive drying will degrade the filament. We recommend storing filaments in a resealable bag with desiccant when not in use and we recommend using a filament dry box like the PolyBox™ when printing. The PolyBox™ is a spool holder / dry box which stores filament in an environment below 20% relative humidity while printing, preventing moisture absorption.

Removing Moisture:

If your filament has absorbed moisture it can be dried in a convection oven. Visit our 'starters guide to moisture, drying and filament storage' for recommended drying times.


Printer Settings


Nozzle Temperature

PETG is considered a medium temperature material, typically printing between 230°C - 245°C.
Of course the printing temperature range of PETG filaments will vary depending on which printer and filament brand you use.

Higher extrusion temperatures will typically result in better flow and layer adhesion, ideal for printing mechanical parts whereas lower extrusion temperatures allow the plastic to cool and solidify faster, beneficial for users interested in overhang surface quality and easier support removal.

When starting we recommend trying a temperature right in the middle of the manufacturer’s suggested settings. If the manufacturer recommends 230°C - 240°C, printing at 235°C is a good starting point. If your extruder can not reach the highest recommended temperature, try printing at the lower temperature. Based on the quality of the print we suggest adjusting ± 5°C at a time.

Troubleshooting Nozzle Temperature

If the nozzle temperature is too hot, you may experience nozzle jams, wisps / stringing on the surface of the print, difficult to remove and fused support material, sagging or poor surface quality on overhangs.

If the nozzle temperature isn't hot enough, you may experience compromised mechanical properties due to the poor layer adhesion, under-extrusion (uneven / rough surface quality) and if the filament is not melting fast enough; nozzle blockages.

Bed Temperature

Printing PETG requires a heated bed at 70°C - 80°C.

We generally don't recommend heating your heated bed above the glass transition temperature of PETG (80°C ). 

Pre-Heating

When printing PETG, pre-heating the heated bed before the print is optional but not required.

Heated Chamber

A heated chamber is not required to successfully print parts in PETG. If your printer has a heated chamber we recommend printing PETG without chamber heating.

Cooling

When printing PETG you can print with the part cooling fan ON or OFF. The best results will vary depending on your printer.

If you are interested in maximizing layer adhesion and strength, we recommend printing with the cooling fan OFF.

Printing with the cooling fan ON will improve surface quality and reduce stringing.

If you can control the power of your cooling fan, even setting the fan speed to 20% can help to improve the quality of overhangs and reduce sagging.

Rafts

A raft is not required when printing PETG materials however if the printing bed is not perfectly leveled, a raft can be used to compensate and improve bed adhesion while minimizing warping.

A raft can also be useful to stabilize tall or fine support structures.

Supports

Self-support (SINGLE EXTRUSION)
When printing both the supports and model in PETG, supports can be broken away by hand.

Multi-material Supports (DUAL / MULTI EXTRUSION)
There are currently no support materials that perfectly interface with PETG.

In some cases PolyDissolve™ S1 will successfully bond to PETG, this success is geometry dependent. PolyDissolve™ S1 is a water soluble support material.

Other Notes
If supports are fusing to the model, try decreasing the printing temperature by -5°C adjustments or increase the distance between the model and supports.

If your supports are failing / collapsing during the print, try increasing support density and printing with a raft , this will improve adhesion for the supports.


Post 3D Printing


Removing a print after completion

Once your 3D Print has completed, it can be removed from the build plate. The best method to remove your PETG 3D Prints will depend on your build platform with some of these methods specific to removing PETG prints. 

Rigid Build Platform
On rigid build platforms like glass or aluminium, a sharp paint scraper can be used to easily remove the model.

When printing on glass, the PETG print should be removed from the glass platform when the temperature is high. Removing a print after the bed has cooled may cause the glass to break because the print may shrink more rapidly than the glass plate.

Some printers are designed so the platform can be removed from the bed while other printers the build platform may be fixed in the printer. If the platform is fixed, we recommend supporting the platform with your second hand to prevent uneven pressure on the bed which could affect your bed leveling.

Flexible Build Platform
Some printers on the market print on flexible build plates. With these platforms users can flex the plate to remove prints.

Removing Layer Lines

PETG like other materials can be post-processed after printing to remove layer lines and achieve a smooth surface.

PETG is considerably easy to sand for professional applications and the process is easier when compared to sanding PLA. In addition printing with finer resolutions and using a filler primer can drastically cut down on sanding / post-processing time.

PETG also be chemically smoothed however the chemicals required are heavily regulated and bring significant health risks.

The process of chemically smoothing PETG is not recommended by 3D Printing Solutions and should only be investigated by industrial users who are prepared to follow all strict safety precautions at their own risk. 

Painting

To paint PETG we recommend printing your part with a plastic primer. After priming, PETG plastics can be painted with acrylic and enamel based paints. For the best results we recommend removing layer lines from your print before painting.

Joining

Parts printed in PETG can be joined together however there are less options when compared to some other plastics.

Glue
To glue parts in PETG we recommend starting with CA glue. We recommend sanding contact surfaces with a coarse sandpaper to increase the surface area for the glue, this will result in a stronger join.


Trouble Shooting


Blocked Nozzle / Filament Jam

When 3D Printing it is possible to encounter filament jams or nozzle blockages, these blockages can be caused due to a variety of reasons.

Causes and Steps to Prevent Nozzle Blockage and filament jams.
In all of these cases if the filament cannot pass through the extruder, the extruder gear will continue to try push the filament and will eventually 'chew out' the filament. If you hear a clicking or clunking sound coming from the extruder, this is a good sign that the filament is jammed or will be if ignored. 

  • If your extruder temperature is too low during printing, the PETG filament will not flow and will have difficulty extruding. Printing with the correct nozzle temperature will solve this issue.
  • If the filament is softening in the hot end, the extruder will 'chew out' the filament, causing a nozzle jam. This issue is known as heat creep, click here to learn more about this issue.
  • If there is too much friction on the filament, the extruder may have difficulties feeding the plastic. Try feeding the filament with a spool holder in different positions (above, beside, behind the printer).
  • If the nozzle height is set too close to the bed, the filament will have difficulty feeding through the nozzle eventually causing a filament jam. When printing at finer layer heights (0.1 and 0.05mm) the correct nozzle height is even more important. To prevent this issue it is important to print with the bed leveled and the correct nozzle height.
  • If the part is warping or lifting off the bed, the part will be pushing against the nozzle limiting extrusion and material flow, in this case it is important to prevent the part from warping.
  • Nozzle Blockages can occur more commonly with finer nozzles. The majority of 3D Printers are equipped with 0.4mm nozzles, it is important when printing or experimenting with a smaller nozzle (0.2mm) to adjust printing speed and extrusion settings 
  • If the filament is of poor quality, is oval shaped or is manufactured with an inconsistent diameter, this can cause the filament to jam in the extruder. The industry standard for filament tolerance is ± 0.05 mm. If the filament is 1.75mm an acceptable diameter variance would be between 1.70 - 1.80mm. Premium and higher quality brands can offer ± 0.02 mm tolerance. If you have difficulties printing PETG with only specific brands of filament this could signify issue with their quality control or could also be related to heat creep or printing with the wrong settings.

Cleaning a PETG Nozzle Blockage
If the nozzle is blocked with PETG one of the most successful solutions is to feed a tougher / harder and higher temperature material (for example PolyMax™ PC) through the extruder. In most cases, the properties of the tougher material and its higher printing temperature help to purge and remove the clogged PETG plastic. It is important to feed the tougher material at its required printing temperature, for PolyCarbonate (PC) this is 250°C and to push the filament into the extruder during this process.

If you cannot remove the blockage of PETG plastic from the nozzle, we recommend swapping to a spare nozzle.

Heat Creep

What is heat creep?

Some users have difficulty printing PETG due to a problem known as heat creep. In essence this issue is caused when heat creeps up the extruder to the extruder gear and softens the filament. Rather than the gear gripping and pushing the filament through the hot end, it will chew the filament out.

Heat creep affects lower temperature materials like PETG due to their low softening temperature of 80°C and the issue is more prominent on printers designed to print high temperature materials, dual extruder printers where a section of filament sits idle for long times or cheap 3D printers with poorly designed extruders.

Solutions to preventing heat creep.

The first step is to make sure the extruder fan is cooling the extruder as intended. If the printer is enclosed, printing with all front doors and top hatches open may help to cool and prevent the filament from softening near the extruder gear. Printing on the lower end of the materials extrusion temperature can also help reduce heat creep in some cases.

Heat creep will be more common when printing parts with retraction. The filament will feed past the extruder gear multiple times with each retraction, this makes it far easier for the extruder gear to ‘chew out’ the filament. Printing simple parts with little or no retraction are more likely to be successful as the filament will only be passing the gear once.

Stringing / Oozing

Compared to other materials like PLA, PETG can tend to flow more easily which can lead to stringing left behind as the extruder moves between points. By controlling the flow of the material we can minimize and prevent oozing and stringing.

Minimizing and preventing stringing.

  • Printing with a cooler nozzle temperature will in many cases help to reduce unwanted oozing as the plastic will flow and solidify at a different rate.
  • By increasing the retraction length or retraction speed in your slicer settings, the extruder will withdraw a short distance filament from the nozzle, helping to prevent oozing when the extruder travels between points.
  • If the spool has absorbed moisture, the moisture will affect the flow rate and viscosity of the material causing unwanted stringing and wisps.

Warping

PETG materials can typically be printed easily on most machines with excellent dimensional stability. In some cases it is possible for PETG materials to warp or lift, lets look at what can cause PETG prints to warp or lift off the bed.

Preventing warping.

  • The most common reason for PETG parts to warp or lift during the print is due to insufficient bed adhesion or an incorrect nozzle height. If the first layer of extruded plastic is not sticking to the bed, a small amount of small residual stress will be enough to lift the part off the bed. It is important to ensure your nozzle height and bed is leveled correctly and that you are using the correct printing surfaces for PETG.
  • Drafts, cool air from air conditioners and low environmental temperatures in winter can cause the material to behave differently and will print with more internal stress. An enclosure with a closed front door can help to maintain the right printing environment.
  • Printing with the heated bed at 80°C will help to heat up the surrounding environment and improve bed adhesion and printing consistency. Depending on the thickness of the bed, some printers will accurately heat the bed to 80°C but in reality the surface of the bed may only be reaching 70°C, with some machines it may be required to set the bed to 90°C.

Poor Layer Adhesion

Causes and steps to improve poor layer adhesion.

  • To improve the layer adhesion of your model you can try printing with a higher nozzle temperature to improve flow and turn off the part cooling fan which will improve the bond between layers.
  • If the filament is under-extruding during printing there will be inconsistencies and gaps between each layer, compromising mechanical strength and layer adhesion. It is important to ensure you are printing the PETG filament at the right nozzle temperature to ensure consistent flow, check your nozzle isn't blocked and to minimize drag or tension which may prevent the filament from feeding.
  • Poor layer adhesion can also be caused when printing a spool of PETG spoiled with moisture. When the filament passes through the hot end, the moisture erupts creating bubbles in the extruded plastic, compromising the parts mechanical properties. If a spool of filament has absorbed moisture, it can be dried however it is important to store the PETG correctly and prevent this issue from occurring.

Parts difficult to remove from platform

To print a successful print excellent adhesion between your first layer and the the bed is critical, but in some cases it can be difficult to remove models if your adhesion is too good.

Causes and steps to improve print removal experience

  • Some print surfaces specifically manufactured for PETG materials are designed to maintain adhesion with the part when the bed is heated and self-release when the part is cool. Try removing the models when the heated bed is hot or cold to see what method best suits your printing surface.

If you are printing on glass however, please always remove the part when the glass bed is HOT.

  • Your heated bed may be operating too hot or your nozzle temperature may be too close to the bed. You can try making slight adjustments to the heated bed temperature or nozzle height if this improves your user experience. Of course this is a fine balance as adhesion between the print and platform is important to achieve successful prints.
  • Some users will use Glue stick on top of their print surface to act as a release agent for part removal.

Filament Links


PolyLite™ PETG Introduction
Buy PolyLite™ PETG

PolyMax™ PETG Introduction
Buy PolyMax™ PETG

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