Strong, durable, flexible and easy to print with. We are talking about the material PET-G , which is among the popular filaments for 3D printing due to its properties. It can be used by home DIYers, but it is also often used in the industrial sector, for printing cheaper functional parts for machines. 

There are many reasons to edit PET-G filament prints . If you are going to print mechanical parts into machines, it is important that they fit exactly. The surface treatment of the prints will help you with this.

A typical example is various screws, holders or various components where the exact size and shape play an important role. Another example is the various covers, which must fit exactly and you cannot avoid surface treatment.

There are various ways to smooth prints from PET-G , but unfortunately, acetone, which is often used, will not work. The PET-G material is relatively highly resistant to common chemicals that are otherwise used for smoothing filaments. Therefore, it is necessary to reach for other chemicals.

PET-G filament hardly twists during printing, but small deformations can still occur, which disappear thanks to smoothing. And the visibility of layer lines will also decrease. Among the equally important reasons is of course the appearance of the prints, thanks to post-processing you can achieve interesting results.

Types of surface treatment: 

Grinding

Grinding is one of the most popular methods of editing prints from different filaments. By sanding, you can remove excess support elements and smooth the surface beautifully. With PET-G, you can try sanding both wet and dry. The advantage of the wet way, when you need to continuously soak the sandpaper in water, is that it creates less dust. In both cases, it is advisable to grind with an even circular motion. Thanks to this, you will be able to achieve a smooth surface. During grinding, fine plastic dust may be released into the environment, which is not ideal to inhale. You can solve this by using a protective mask, glasses and protective gloves, which will protect the skin of the hands.

Detailed instructions and tips on what and how to grind prints can be found in this article: How to adjust the surface of PLA filament prints . 

Grinding has one disadvantage – for large prints, for which PET-G material is often used, it can be a lengthy process.

Advantages

  • available
  • simple

Disadvantages

  • time consuming
  • fine plastic dust is released and dusted during the process

Polishing

Polishing is actually the next step after grinding. Because in order to be able to polish the print quality and the polishing material to hold well, the print needs to be sanded smooth first. This is achieved by using high-grit sandpaper for sanding. You can sand by hand, using a classic cloth, or you can use an electronic polisher for this.

The process of polishing with a cloth is simple - apply the polishing material to a soft cloth and apply it to the print in a circular motion until it is absorbed. Then run a clean cloth over the entire surface of the print to achieve maximum shine. The disadvantage is that manual polishing can be more physically demanding and sometimes you will probably need to exert more force, so you need to be careful with fragile parts.

An electronic polisher will save your hands, but the question is whether you will use it often enough to make the initial investment worth it. If you're printing mostly small models, a regular electric nail grinder might work just fine. 

Polishing with a cloth

Polishing with an electric sander

Advantages

  • available
  • cheap

Disadvantages

  • time and physically demanding
  • not suitable for a more fragile model

Advantages

  • faster in time
  • not physically demanding

Disadvantages

  • starting investment
  • some skill required
  • electricity the nail grinder is not suitable for larger models

Epoxy resin

If sanding didn't catch your eye, you can try smoothing the print using epoxy resin , which not only smooths the print, but also covers small deformations, grooves and print layers. Epoxy resin has a self-leveling property, that is, it creates a uniform layer, thanks to which brush strokes will not be visible on the print. Epoxy treatment provides a shine, but also a harder surface, so it partially protects against impacts.

After applying the epoxy, it is necessary to let the models dry sufficiently, and then it is up to you whether you will continue with the modification and further sand or varnish the prints, or whether the epoxy treatment will be a sufficient solution for you. And if you want to play more with the epoxy resin, it is possible to mix powder with a metallic effect or various colored pigments into it.

Advantages

  • not physically demanding
  • protect the print
  • ensures a shiny surface

Disadvantages

  • the need to take into account hardening
  • the epoxy mixture must be prepared before use

Spray paint

Another modification option that we must not forget is spray paint. Spray paint will be appropriate to use if you want to have the final model in a single color design. Although, of course, it is possible to cover the places where it is not desirable to be colored, with insulating tape. But it may not work 100%.

For multi-colored models, it may be better to use a brush application. Applying spray paint will require some experience and skill to achieve uniformity.

Immediately after applying the paint, and before it dries, you can spray the model with colorless polyurethane, which will ensure the smoothing of unevenness and the print and protect it from weather influences and sunlight. It is advisable to place the model in front of a fan so that the paint cannot run off.

Advantages

  • not physically demanding
  • protect the print
  • ensures a shiny surface

Disadvantages

  • the need to take into account drying
  • the need for experience and skill in spraying

Heat treatment

This is a method that is a little more difficult to perform, so it may not be the right choice for everyone, but it is still worth mentioning. Heat treatment is carried out using a hot air gun , for which it is important that it has the ability to set the precise temperature control. The principle is that the temperature must be very close to the melting point of the filament (which is around 240°C depending on the brand of filament), but must not exceed it to avoid damaging the print.

Another disadvantage is that you need to have enough skill to keep the gun at the same distance and circle the model with smooth movements. If you succeed in all this, the thin layer on the surface of the print will unite. In the beginning, we recommend that you try everything on a test model and start with a lower temperature setting to avoid the disappointment of a ruined print.

Advantages

  • quick execution
  • no need to let dry or harden

Disadvantages

  • difficult to implement
  • the need to purchase a quality heat gun

Chemical pathway

Although PET-G filament is one of the materials that cannot be smoothed with acetone, you still don't have to give up on the idea of ​​smoothing using a chemical method. There are other chemicals that can handle PET-G. The catch is that these are substances that are dangerous and you can only buy them if you have a special permit.

A frequently used alternative to acetone is ethyl acetate, but this may not affect PET-G. Another variant is dichloromethane, methyl ethyl ketone (MEK), toluene and cyclohexanone. PET-G will dissolve all of these substances, but, as we said above, these are dangerous substances that should only be handled by trained professionals.

Smoothing with chemicals can be done in several ways:

  • Using brush application

Applies if dichloromethane is used (PET-G does not twist and the chemical substance does not leave traces on it, higher solvent consumption).

  • Wet wipes or towels

Napkins and towels are soaked in the chemical and placed around the model.

  • Smoothing box with solvent fumes

You can buy professional boxes or make your own smoothing box at home.

It is not recommended to directly submerge the print in the solvent, as removing the print may burn the skin, and there is also a high chance that the print will be seriously damaged.

Advantages

  • quick execution

Disadvantages

  • working with chemicals can be dangerous
  • available only by special permit

 

Bonding

This is no longer a classic surface treatment, but it is still good to know what PET-G models can be glued with.

Unlike, for example, ABS or ASA , which you can easily glue with acetone, classic solvent glues cannot cope with PET-G. The solution is instant or cyanoacrylate adhesives .

The gluing procedure is simple - apply the glue in thin layers to the edge you want to glue. Alternatively, you can apply it at regular intervals.

If excess glue remains on the print, wipe off the excess glue with a paper towel. You have to act now because instant glues dry really fast.

Another possibility is to use a two-component glue , when it will be necessary to mix the resin with the hardener. The disadvantage is that preparation (mixing of glue) is required, so it is often used on larger surfaces. Sometimes a longer curing time is required (depending on the brand used and the ratio of epoxy to hardener). Epoxy glue can also act as a surface layer that smooths out unevenness on the print (we already wrote about epoxy resin above ).

Gluing with instant glue

Gluing with two-component glue

Advantages

  • available
  • quick drying

Disadvantages

  • not suitable for larger sizes

Advantages

  • the possibility of using it all over the surface and thus smoothing the surface

Disadvantages

  • sometimes a longer curing time
  • necessary preparation (mixing)