Smooth PLA Through the Fire and Flames

3D printing makes it easy to produce complex geometries, but the fused deposition methods generally create parts with poor surface finish, largely due to the layers being highly visible in the finished part. There are a wide variety of ways to deal with this, often involving sanding parts after production, or the use of fillers and paints. [XerotoLabs] has another solution. (YouTube, video below the break.)

To smooth the parts, a butane torch is pressed into service. The flame temperature is kept fairly low, and the torch is used almost like a brush to evenly apply heat to the surface of the part. As the PLA reaches its melting temperature, surface tension helps to smooth the part out. This is very similar to flame polishing which is commonly used in the fabrication of acrylic plastics.

It is a technique that requires some finesse – too much heat or focus on a single area, and you’re liable to end up with a molten plastic blob instead of a nice shiny finished part. Precautions must also be taken to avoid burning yourself or your workshop to the ground. But it’s a useful tool to have in your kit when you’re producing PLA parts that you want to look their best.

We’ve seen other techniques for smoothing PLA, too – the solvent method is particularly interesting.

17 thoughts on “Smooth PLA Through the Fire and Flames

    1. The aim is to have a hot enough flame to only melt the very top layer of plastic. If you heat the whole part it will warp horribly and be useless. So you want MORE heat, like a flame. I’ve tried this and it ends up looking horrible, about the same effect as painting it with a clear varnish and doing a very bad job of it, pools and drips and blobs. Not as perfect as primer + sanding and paint by any measure.

  1. I have tried this in a few different way’s and what I end up with is as soon as it starts, it releases internal stresses from printing and warps almost every single time

    now just cause I suck at it, does not mean its impossible

  2. Interesting. I tried something similar with a small heat gun but it didn’t work very well. Maybe what does the trick is the higher temperature concentrated. A ‘general hot wind’ , like the one I tried, had no effect on the surface but made the entire region soft and flexible.

  3. I once tried using a heat gun to smooth surface but it didn’t work like in the video. The surface finish wasn’t influenced at all, but it made the entire region soft and malleable. Maybe what does the trick is higher and more concentrated heat then.

  4. At least PLA fumes are generally better than ABS.

    https://3dprintingindustry.com/news/toxic-abs-pla-fumes-3dsafety-org-inquires-vocs-60796/

    “The new study, presented by Dr. Fabrizio Merlo and Dr. Eng. Stefano Mazzoni, builds on previous research which demonstrated that during the fusion and processing of plastic materials, several toxic particles are released as gases, including ammonia, cyanidric acid, phenol, and benzene, among others.

    The lab tests showed that ABS is significantly more toxic than PLA, but that the corn-based polymer is not exempt form dangerous emissions, especially if extruded at temperatures higher than 200°C. Furthermore (as may be expected), the same material spools, when acquired from different resellers, release very different quantities of VOCs, even if used in the same 3D printer and under the same parameters of speed and temperature.”

    1. Then again, ABS allows smoothing in other ways. Using acetone for example. Impossible with PLA, to smooth PLA with vapour you’ll need Ethyl Acetate or THF (Tetrahydrofuran) which are way more dangerous then acetone.
      So it all depends on how you look at it…
      But more important is that you are aware of the limitations of both PLA and ABS and depending on what you are attempting to make decide which is the best choice. Because in the end it may matter how long it lasts and how well it performs under certain conditions (temperature and stress).

      1. you can actually smooth PLA with acetone washes, just not as easily as ABS. Ive done it and there are a variety of videos showing it being done. Much preferable to those igher powered solvents.

  5. I wonder if there is a way to instrument this process so you can get consistent repeatable results. Like a little cyclone blast furnace you suspend the part in, then an Arduino controls fans, gas flow rate and burn time.

    Sounds exceedingly dangerous :-)

  6. I’ve been using a standard lighter to get rid of the stress points where the supports were attached.
    Well now the slcier is tuned so I nearly don’t need it anymore.
    Could be worth trying a propane gas weed burner with big flame wuickly over the whole print

  7. There is a process called thermal deburring used for machined metal parts.
    Newly machined parts are put into a chamber where a gas and air mixture is ignited cousing a controlled flash combustion that raises the temperature momentarily to melt small edges or burrs. I wander if the same process could be used on PLA plastic.

  8. I’ve used a hot air gun to remove some stringies (from printing too hot, I think). That worked well, but for smoothing it really didn’t, for me. Too low would just soften the print and it would droop, too high would burn it so the surface looked like a roasted marshmallow.

  9. Ha, Hari Told me my video got over here .lol. Flame polishing is something I still mess up. but it can add some great strength, especially on smaller parts that a heat gun just can’t get. I don’t have a rework station yet, but I expect a small tip on decent airflow would have the same effect as the good/sweet spot of a flame without much risk to cooking / burning the PLA
    I think a hot air in a small nozzle is much the same as the hot air in the sweet spot just ahead fo the flame in a micro torch.. The real advantage of the micro torch for me is that is like using a small paintbrush.

    > my other Hackaday project https://hackaday.io/Xeroto

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