Surface treatment of ABS / ASA using acetone and other techniques

Properties of ABS / ASA filament and what you can use it for

If you've been around the world of 3D printing for a while, you've definitely come across ABS and ASA filaments . It is a frequently used material among printers, which has gained popularity thanks to its toughness, mechanical and temperature resistance (and in the case of ASA, resistance to UV radiation). Both ABS and ASA are among the cheaper filaments and you can choose from a wide range of different colors. For printers who emphasize not only functionality, but also appearance, the good news is that both ABS and ASA work well . All this makes them a material suitable for mechanical parts that are under more stress.  

But since nothing is perfect, even this filament has its drawbacks – it curls quite a lot, smells bad when printing, and emits dangerous fumes. These are the reasons why it is advisable to use a printer cover and have a well-ventilated room.

Printing doesn't stop there

Post-processing (that is, additional editing of the 3D model after printing) is a separate chapter that can sometimes take quite a lot of time, but the time and work you spend on it will return to you in the form of a professional-looking print with a beautifully smooth and shiny surface. There are several ways to reach this goal. You just have to choose which one you want to marry.

Grinding

Sanding (whether with a nail file or an electronic sander) is one of the traditional styles of finishing prints.

This is a simple operation that even a beginner can do. And the tools you'll need for it are readily available.

Its main disadvantage is that it takes a lot of time, and it is not possible to edit multiple prints at once. We described more about sanding in the article: How to adjust the surface of PLA filament prints .

Advantages:

  • simple
  • available
  • not financially demanding

Disadvantages:

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

Sandblasting

The sandblasting method works on the principle that a sandblasting gun sprays an abrasive material onto the print, which sands the model smooth. For example, glass ballotine (glass microspheres), artificial corundum powder, ceramics or crushed shells can be used as abrasive material. There are blasting booths in which both the automatic sandblasting process and manual settings can be used. But these are professional devices that are used in the industrial sector. Another option is smaller sandblasting boxes, which are commonly available on the market and will not be such a big financial investment. And if you are a do-it-yourselfer, you might be interested in the last option, which is a home-made sandblasting box, for which you can find manufacturing instructions on the Internet. 

Advantages:

  • not physically demanding
  • it won't take too much time

Disadvantages:

  • the need to purchase equipment for this
  • it gets very dusty during the process - it must be done in a closed box
  • in the case of a professional cabin, a high purchase price

Smoothing with acetone vapors

If chemistry is or was one of your favorite subjects at school, this method will surely interest you. But even for those for whom chemical formulas are one big unknown, the smoothing method using acetone will be interesting. It is not at all complicated, is often used and takes relatively little time. However, it also has its drawbacks.

Acetone vapor smoothing can also be used on other materials (such as PVB or Polyvinyl Butyral), but it works best on ABS or ASA .

Acetone is a colorless, flammable substance with a typical odor that is most often used to remove paint, degrease and clean surfaces. It is definitely not a good idea to apply acetone directly to the surface of the print. This is because it would be deformed, as acetone is an aggressive solvent. And that's why vapors are used for smoothing, which will ensure the print has a beautifully glossy, porcelain-like appearance. The fumes must be in a sealed container, so you have two options:

  • build your own smoothing box
  • buy an already assembled professional smoothing box

It's time to talk about the disadvantages of this method. One of them is that it can sometimes be difficult to estimate the appropriate moment to end the process and there can be too much smoothing and loss of dimensional accuracy or small details on the model. You also need to think about this when you decide which method to smooth your print. Another negative feature of acetone is that it is a flammable and dangerous liquid, which you need to work with carefully and follow all recommendations.

Advantages : 

  • faster process
  • the ability to smooth multiple prints at once 
  • even smoothing
  • leaves a shiny surface

Disadvantages :

  • acetone is a dangerous substance
  • small details and edges may be lost
  • the need to let the prints dry
  • high initial investment for a professional smoothing box 

Professional smoothing device

This is a box where you put your prints and select settings on the touch screen. Among the advantages of the purchased smoothing box is that it is easy to operate, increases the safety of working with acetone, and thanks to the circulation of vapors inside the box, the model is smoothed evenly. The disadvantage of a commercial smoothing box is clear - it is not a cheap thing at all. There are two brands of smoothing boxes available on the market: Polysher and  Zortrax . 

Advantages over a home box:

  • simple operation
  • even smoothing
  • safer use
  • without having to control the smoothing process

Disadvantages compared to home boxing:

  • high purchase price
  • small selection of brands on the market

Custom smoothing box

If you are not a die-hard fan of this method, or you will not use a professional box in large volume, you will probably go the other way - build your own smoothing box at home.

Advantages over professional boxing:

  • a cheaper option than professional boxing
  • the possibility to build the box size you want

Disadvantages compared to professional boxing:

  • greater security risk
  • the need to try the process and find the right procedure

Safety above all else

As already mentioned, acetone is a highly flammable substance that ignites easily, so it must not be in the reach of an open flame. Even a small spark could cause big problems.

Don't forget about proper storage either. Acetone containers must be stored in cool, well-ventilated areas, away from direct sunlight and other heat sources. 

Inhalation of acetone vapors can cause dizziness, skin irritation, drowsiness and nausea, among other things. That is why it is necessary to protect yourself when working with acetone - use protective gloves , a face shield or mask and glasses .

If you are still determined to try making your own smoothing box, preparing the box itself is not difficult at all. For production you will need:

  • acetone

High purity 99-100% acetone is needed. If you were to try to use diluted acetone, you would not get the desired result, because the diluted acetone is not strong enough to create vapors and will not smooth the prints.

  • paper towels

The idea is for them to soak up the acetone and help with evaporation, so any paper napkins or tissues will work well.

  • magnets

These will be used to hold the napkins/handkerchiefs on the sides of the container. You put one from the inside, the other from the outside, and then you just let the magnetic force work. Choose the size and strength of the magnets according to how big and how thick your container is.

  • vessel

The size of the container depends on the maximum size of the prints that you will be smoothing. You can also buy multiple boxes in different sizes. It will be great if you can get a container with a lid to keep the acetone fumes inside the container. If that doesn't work, you'll have to use a plate that you tilt over the container. But be careful - the lid must not seal completely. The vapors will increase the volume, so it is necessary to have small holes in the lid.  

The material of the container needs to be chosen so that it does not react with acetone. You can choose a glass container or a polypropylene box. It is important that the container is transparent so that you can monitor the smoothing process as it progresses.

  • Aluminium foil

Prints need to be placed on a raised stand to ensure they do not touch the liquid acetone. The chemical reaction happens quickly, so it would only take a short time for the print to come into contact with the liquid and it would be etched and destroyed. The base must be made of a material that does not react with acetone. The aforementioned aluminum foil or another metal or glass substrate will be suitable for this. The base needs to be raised, for this use again some material that does not react with acetone (metal, PLA, glass, etc.).

Another accessory that is no longer necessary, but you can use it to speed up smoothing, is a fan . Fumes tend to stick to the bottom of the box, which can cause the bottom of the print to be nicely smoothed, but the top still has visible layers from the print. The fan thus ensures a balanced flow of vapors and thus even smoothing of the surface over the entire model. But be careful - since this is an electronic machine, you need to check that it is not damaged in any way and that a spark cannot jump off it that could ignite the acetone. 

You've got the theory behind you, now you can get down to business.

Spread the paper napkins evenly in the box and hold them with magnets on the sides. Be sure to leave a section uncovered so you can watch the smoothing progress. Insert a raised pedestal into the box and carefully pour a small amount of acetone into it . You begin to swirl the container slowly to ensure that the liquid soaks into the napkins. The liquid should not come into contact with the skin to avoid irritation. All the liquid should be absorbed into the napkins. Place the print on the stand, you can add a fan, and close the container.

Another option to speed up evaporation and ensure even smoothing is to heat the container with acetone. But because acetone is very reactive to heat and could easily catch fire. You need to think about safety - heat gently and never put the heat source in the container. For heating, use, for example, a slightly heated metal pad. But it should never be directly hot. Attention! If you decide to heat the box, do not leave the lid completely sealed. If you are not sure about the procedure, ask a more experienced printer for advice, or just to be safe, skip this step.

And now it's time for a well-known proverb - patience brings roses (in our case, it will be beautifully smoothed prints). Now you need to let the acetone do its work and start dissolving the surface of the print. The usual smoothing time can last from about half an hour to several hours. How long you wait depends on several factors:

  • print size
  • container size
  • ambient temperature
  • to seal the box

The smoothing process needs to be monitored throughout. Firstly, from a security point of view, secondly, so that you can estimate in time when the printout needs to be taken out. Leaving it surrounded by acetone fumes for too long can cause permanent damage to the print.

If it seems to you that the print is sufficiently smoothed, check that the room is properly ventilated, open the lid of the box and carefully take the print out. Be careful not to let the acetone-soaked wipes come into contact with the print or the skin. 

Remove the print using a stand so you don't have to touch it, as decals may remain on it or other damage may occur. Here you need to let the print dry so that the acetone evaporates.

The drying time is different again. It can be several hours or several days. Since acetone has a strong smell, this typical odor can remain on the print for some time. But don't worry, it will clear up sooner or later.

In conclusion, it is necessary to remind that working with acetone can be dangerous and it is always necessary to think about compliance with safety rules. If you are unsure about anything, it is better to consult with an experienced printer.

Acetone-smoothed prints tend to be beautifully smooth and shiny. Don't be discouraged by the first failures, sometimes you need to try and try before you fine-tune the right procedure.