3D Genius

By April 18, 2013 10 Comments

A smoothing solution for PLA? We’re still looking…



It’s well known that ABS filament can be smoothed after printing by immersing the printed object in acetone. This process melts the surface of the object, blurring the layers together to produce a less accurate, but very much more smooth result. After the application of acetone, ABS frequently looks like it has not been printed.

Which is all very well for those who use ABS, but more and more printer manufacturers are turning to PLA as their filament of choice, for its superior printing qualities – it prints at a lower temperature, and generally doesn’t require a heated bed since there’s far less occurrence of the material curling up during the print process. The only problem with PLA is that acetone has little effect on it; there is, it seems, no way to smooth PLA in the same way.

And so we were particularly intrigued by the Kickstarter project for the 3D Refiner, which claims to “transform any 3D print into a high quality beautifully finished part in a fraction of the time” – the idea being that you can print a low resolution model, and then smooth it so it looks like a high resolution model. In the FAQ the developers explain how PLA can be smoothed using MEK (Methyl Ethyl Ketone), a high strength industrial solvent. Intrigued, we decided to try MEK out for ourselves to see if it worked.

Warning: Should you be planning to experiment with MEK yourself, be aware that it’s seriously nasty stuff. You should be sure to work in a well-ventilated environment, due to the unpleasant fumes, and to wear chemical-resistant gloves. Be especially careful not to splash it on your skin, and do wear protective eyewear.

A: The initial model

This is the model we started with – an elongated hand. You can clearly see the roughness on the left of the fingers, especially; these are the printing artefacts we were hoping to get rid of.

B: MEK painted on with a brush

Although it seemed at first that some smoothing was indeed taking place, once the hand was dried it became clear that very little smoothing was happening, if any. The white deposit instead served to exaggerate the unevenness of the surface.

C: One minute immersion in MEK

Immersing the whole hand in MEK did produce some slight smoothing of the surface – the fine lines between the printed layers are now slightly less apparent, and the hand feels quite a lot smoother to the touch. But the white deposit has now become worse, and the overall effect is very unappealing.

D: Five minute immersion in MEK

No significant improvement in smoothness was evident after a long immersion; the only real outcome was that the model became significantly weaker, to the extent that the index finger snapped off during the drying process.


MEK does not seem to be a viable solution. There may well be a smoothing agent that blends the layers of a PLA-printed object, but we haven’t found one yet. We’re still looking.

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10 Comments on "A smoothing solution for PLA? We’re still looking…"

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  1. rojer says:

    So my question still stands. What about dipping the part in a photo-reactive polymer? There are several liquid resins that emulate other plastics, such as ABS, that if viscous enough, might coat well enough to hide blemishes. Perhaps one could just dip it and then set it out in the sun for an hour – or buy the proper curing lamp. Although the resins aren’t cheap and may require a gallon’s worth of purchase, it would likely cover a large number of objects. I don’t know anything about the resin properties, but I know that there are several formulas and colors available and many cure under normal light. What do you think?

    • Perry Engel says:

      PLA smoothing using a coating of a photopolymer would probably be less cost effective than say a epoxy or some other thin “laquer”.
      If the intent is to apply a thin coating of something to the object, then the simplest solution is to have an air dired
      coating dip, followed by the object on a rotational rig that rotates in both axis’.(similar to what is used for rotational molding (kayaks etc))( Air dried allows a can of the dip to be closed and then used on the next dip. epoxies have to be used once the two parts are mixed.)
      A dip and rotate to dry would ideally be uniformly distributed
      on the model, and would allow much more choices of the laquer, time to dry (which would allow for less toxic solvents etc).
      of course a dual axis forational rig is needed but can be made really cheap for 3d print sized objects.

      • Steve Caplin says:

        The problem is finding a solvent that smooths PLA in the same way that ABS can be smoothed with acetone. Once we find something that will do the basic job, we’ll be able to go on to come up with rotational air drying rigs to perfect the technique.

        • Perry Engel says:

          I was proposing a coat of some off the shelf
          laquer or epoxy or some other air dried or “binary”
          compound because the solvents for PLA seem so toxic.
          My objection to photopolymers was merely the cost. Photopolymers and a rotational rig would offer the best
          of even distribution, and control of the hardening.
          This would allow one to get the coat applied and allowed to evenly distribute before setting.
          That being said any solution using this method could have
          a coat applied followed by say a gas that cures the coat
          or infrared heat lamps etc. The main thing is to get a thin even coat at a low a cost as possible and not have it be a toxic mess!) The proposed MEK rig seems toxic and costly to impliment(i mean the refiner mentioned in the article). a dual axis rotational setup could be easily made by laser cut and use a single cheap motor. No microcontroler would be needed.

          • Steve Caplin says:

            But you have to admit, it still sounds very nasty – the idea of MEK as a gas seems incredibly toxic!

  2. Corne says:

    I don’t really know where you got the strange idea that MEK is so very toxic. Safety wise, you should treat it in the same way as you would acetone. The material safety data sheets recommend similar treatment (well ventilated area, wear gloves, avoid sparks).

  3. Ash says:

    Hackaday reports that Tetrahydrofuran acts in a similar way on PLA as acetone does for ABS. Placing some in a container with the part and gently heating will smooth it out. THF is apparently no more toxic than acetone.

    • Steve Caplin says:

      This is a new one on me. I’ll certainly check it out. Is Tetrahydrofuran sold with a proprietary name, or with a standard household function?

    • Mac says:

      THF is nasty, nasty stuff. I reported that Hackaday article in the hopes of having it taken down. THF is a mutagen, you don’t want to get anywhere near that. Enormously more dangerous than acetone (which deserves respect in its own right).

      Fortunately some folks have replied about the dangers of that Hackaday article since it went up, but it should still be removed, in my opinion.

  4. Aaron says:

    I wouldn’t have thought that MEK was a great solvent of PLA, MEK is traditionally a solvent of choice for styrene based plastics, ABS being one of them.

    If MEK “nearly” worked on PLA, with the whitening that MEK is famous for when used a fusing solvent. I would suggest another appropriate guess as a smoothing agent for PLA might be tetrahydrofuran (CH2)4O (CAS 109-99-9).

    Granted, you don’t want to drink this one either, but we’re not talking about necessarily being safe for consumption, we’re taking about doing a job.

    As a bonus, it is also sure to smooth ABS too, more aggressively than Acetone though.

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