How to Smooth PLA to a Mirror Finish

Need to make your prints look super smooth? Or perhaps, you just want rid of those layer lines to make your print look more 'factory finished'? Here's how to polish PLA 3D prints to a shine you won't believe was ever 3D printed. 

The best way to smooth 3D prints.

It's often said that ABS is easy to smooth (using acetone baths and similar methods) but that PLA and similar non-acetone-dissolving 3d printer filaments cannot be smoothed the same way. They can, you just need to know the right technique, and have a little time on your hands. 

We recommend smoothing using this technique for your most prized prints, as it can take a little bit of time. Additionally, this technique for you to smooth 3D print (PLA filament) does not work as well on very intricate prints. 

Here's a close up of the finished effect. The filament is our Gold/Bronze PLA. This is a 6cm long 3D Benchy for scale, and we only smoothed one side of the hull to compare. 


Polished 3D Benchy

(it's hard to see just how smooth this surface is, but honestly it's like glass)


What you'll need:

To start, you're going to need a selection of fine grit sandpapers. We suggest the following grit sizes (and if you want a really smooth finish like above, we recommend not skipping any steps): 200, 400, 600, 800, 1000, 1200, 1500, 2000, 2500 and finally 3000. 

It's best if you can use 'wet & dry' paper (black grit as opposed to beige effect) especially with PLA, because if you're sanding fast, heat can build up and effect the smooth surface you're trying to achieve. Wetting the glass-paper will lubricate and cool the surface you're sanding. This is not as necessary with smoothing higher temperature 3D printing materials, but still advisable. 


1. Start with the coarsest sandpaper, approx 200 and smooth the surface until you cannot feel any printing layer lines at all. You've got to sand in a circle motion, as you don't want any lines from the sandpaper effecting the surface later on. 


400 Grit Sandpaper 3D Print

 (this is what your print will look like after using 400 grit sandpaper, you cannot see the layer lines)


 2. Start scaling up the grit number. Once you've got an acceptable result with the 200 or 400 - move higher up and smooth the print in increments. Don't skimp on the time to sand them down, and keep going in the circular motion. Try to be mindful of details so you don't loose definition as you go. 

The good news is with each finer grit, you don't need to spend as much time sanding that layer. 


1000 Grit Smooth

 (after using 1000 grit sandpaper it'll start to look really smooth)


3. Keep working up the sizes, from 400 to 600, then to 800 and upwards. Don't miss out steps when you get to 2000. It'll feel really smooth, and will polish nicely at that level - but if you want mirror finish you need to build to 3000. 


3000 Grit Smoothed 3D Benchy

(here you're at 3000 grit, you can start to see the shine before you've polished)


4. The final and most fun stage is the actual polishing stage. Layering up those sandpaper increments doesn't feel like you've made much progress, but once you polish up - the final finish looks great. 

The polish you need to use to really smooth out 3D prints to that mirror finish we've found is just any good liquid metal polish. Our favorite is the ol' trusty Brasso. 


Brasso To Polish 3D Prints


The technique to polish your prints is simple. Get a soft cotton cloth, and apply a small amount of liquid polish. Then apply to your 3D print surface in small circles until all the polish is rubbed into the surface. 

Once you've finished that, the surface should look reasonable shiny. The final stage is to buff up that surface into that mirror polish shine. Just get an unused area of your cloth, without any polish on and go back over the area you've just worked on to buff up to a shine. And that's it. 

Here's a before and after reminder on the technique: 


Before and after smoothing and polishing PLA prints


Hope you found this guide to smooth out 3d prints useful. If you did, why not subscribe to our blog to receive updates on other helpful 3d printing how-tos. 

Please comment below if you have any tips to add or questions, we'll be only too happy to help. 

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