image source Getting a Slick Look to ABS 3D Prints with Acetone Vapor Finishing

5/14/2014

3D Prints that Look Like Toys?

One of the issues with 3D printing, and particularly with the FDM/FFF technology used by most entry-level 3D printers – is the appearance of the final product. (Please see the blog post at www.tesseract-design.com/subtractive-manufacturing.html for a more detailed discussion of how FDM/FFF works.) Even with more costly 3D printing techs, like drop-on-powder printers, the final product can look a little rough around the edges. I heard one professional 3D printing house say that they will only print in white, because any other color makes the final print “look like a toy.”

This is particularly true with ABS prints, because ABS plastic is used to make a lot of consumer goods, including toys. Furthermore, the layering that is part and parcel of the FFF technology can also be very noticeable, especially if the print resolution is low, or if the printer is not properly calibrated – or if the original digital design file wasn’t that good to start with. The final product can come out looking pretty cheesy. This can be especially frustrating when a lot of time and effort has gone into making a 3D print, and it comes out looking like a cheap cereal-box toy.

Acetone Vapor Finishing

Fortunately, there is a way to overcome some of the flaws and drawbacks to 3D printing in ABS, even at low resolutions. ABS plastic is soluble in acetone, a common solvent available in any hardware store. (An old model-builder trick is to use acetone rather than model glue as it fuses the parts together and doesn’t leave unsightly glue gobs.) Acetone can also be manually applied to the finished ABS model, but the results can be uneven and smeary.

A better way to approach the problem is by using vaporized acetone to uniformly melt and smooth the surface of the ABS model. The results are much nicer-looking, and generally less time-intensive than hand finishing, although there are certain safety procedures that need to be carefully followed.

Finishing ABS 3D Prints

The first time I tried acetone finishing was on a print from a scanner that was relatively low-resolution. The 3D print came out perfectly, but the source file was low-res, and the resulting print looked pretty rough. Since there was no way to get a new scan, I decided to see if acetone vapor finishing would help. Here are the steps I used to get a good finish to my ABS 3D prints.

Acetone vapor finish 3D prints

Same print, different finish – the print on the left was printed at low resolution (0.3mm) with acetone vapor finishing, the one on the right with medium resolution (0.2mm) and no finishing

Safety First!

First and foremost, you need to be very careful in handling acetone. Acetone is extremely flammable – do not use near an open flame, and always keep a fire extinguisher handy. Also, acetone can be an irritant to the eyes and respiratory system – be sure to use it only in a well-ventilated area.

Step-by-Step Guide

I went down to the local Goodwill and got almost all of the things I needed for this process for just a few dollars:

  • A hotplate
  • A large metal pot
  • A tempered glass lid
  • A small dinner plate
  • Some aluminum foil

Once I had the materials in hand (as well as the ventilation fan running and the fire extinguisher close by), here are the steps I took:

  • I put the metal pot on the hotplate and poured ~2 ounces of acetone in the bottom. Then I placed the dinner plate in the bottom so that the 3D print would not be sitting directly in the pool of acetone (it would melt). I also made a “heat shield” by folding some aluminum foil over and placed that on the plate. Just in case the print melted slightly, didn’t want to have to chisel it off the plate. (As it turned out, this wasn’t an issue.)
  • I turned the hotplate on to its lowest setting. Acetone has a relatively low boiling point, and it started bubbling almost immediately. The trick is to get a good cloud of acetone vapor built up in the pot before placing the print inside. I waited until I could see acetone condensing on the glass lid before taking the next step.
  • I turned off the hotplate and placed the 3D print onto the aluminum foil heat shield on the bottom. At this point, the residual heat of the hotplate kept the acetone bubbling for enough time for the print to finish. Also, I slid the lid to one side to allow the acetone vapor to escape. The idea is to keep a fresh flow of acetone vapor moving over the print. On earlier trials, I hadn’t allowed for an escape vent for the vapor, and it condensed on the horizontal surfaces and dissolved the ABS.

    Acetone vapor finishing problem

    Be sure to vent the acetone vapor or this pitting/bubbling might happen when the vapor condenses on the print!

  • I kept checking on the progress of the smoothing by shining a flashlight into the pot. The smooth gleam was noticeable on the 3D print almost immediately. The process had good results after just 5 to 10 minutes. I’ve seen some instructions that advised leaving the print in the vapor bath for upwards of an hour. This seems way too long based on my experience; I’m surprised those prints didn’t dissolve entirely!
  • I removed the lid from the pot and the pot from the hot plate, and set it in front of a fan to cool it down and remove any residual acetone vapor. In 15 minutes I could remove the finished print from the pot. The aluminum foil was easy to remove from the bottom of the print.

There was then the requisite cleanup and ventilation of the work room, but I was very pleased with the results. It’s nice to have some options in how your 3D print will be finished. Personally, I like the matte look of a high-resolution ABS 3D print, but the shiny, slick appearance of an acetone vapor-finished print is not without its charms as well. Better yet, this can be accomplished with a low-resolution print just as easily as with high-resolution, resulting in a substantial savings in time during the 3D printing process.

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For more information on 3D printing and services offered by Tesseract Design, please see www.tesseract-design.com/3-d-printing