Surface finishing of ABS and PLA

[Travis]

I've tried sanding and acetone with both PLA and ABS.  My results are spotty.  Any tips from the pros?

For ABS, acetone smoothes and shines the surface, but also leaves patches of white film here and there.  Too much acetone causes the ABS to lose integrity and become squishy for about a day or so.

On PLA, I tried sanding + a quick acetone dunk.  The surface didn't become shiny, like ABS does, but it did smooth and waterpoof surface pretty well.  The part didn't melt as much as ABS did.  The previously clear surface became hazy.  There was a marked white reside, as with ABS.

Is there any printer + surface finishing that results in a glasslike appearance for multilayer PLA prints?

[JohnA.]

I don't know of anyone who has gotten truly smooth results.  Lower layer heights help, but in the end it's hard to hide the layers, even on commercial FDM machines.

That being said, tons of people have sprayed ABS parts with a few coats of primer and sanded them down smooth, and you'd never know they were FDM parts.   It's not perfect, but it works.

JohnA.

[Whosawhatsis]

PLA is not acetone-soluble, so you will not get the same results with acetone on PLA as with ABS. The white spots on acetone-treated parts seem to be due to moisture. I think a warm, dry environment is best for drying the acetone. Don't blow on it.

If you make an ABS slurry using some of your waste plastic dissolved in acetone (nail polish bottles are good for this) you can brush that on, and it will work better for smoothing parts than just acetone. It's also great for gluing (actually a solvent weld) printed objects together and can make them much stronger, preventing delamination. I've also used this to repair broken ABS casing on consumer electronics.

None of this will work for PLA, of course. The only solvent for PLA I've heard of is caustic soda, which you wouldn't want to use in the same way. Despite the smell, acetone has surprisingly low toxicity (though it is highly flammable, so be careful).

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[Joseph Chiu]

If you're trying to get a "polished smooth" look, you might need to
use a super-fine polish and a little bit of buffing. That's what I
used to do when I cut acrylic sheets and needed to make the cuts look
clean -- a little polishing compound and a dremel with a buffing tip
worked wonders.

As a first-pass test, try sanding the surface flat with fine
sandpaper, and then polish with toothpaste on your fingers and rub
away.

[Whosawhatsis]

All that sanding isn't necessary. When you soften the plastic with acetone, the surface tension will cause it to smooth itself and make it shine. Just be sure to print with a few extra shells so that the walls aren't thin enough to be deformed before it does. The pre-disolved abs acts as a filler so that you don't need to get the acetone so deep to smooth the ridges.

[akr...@yahoo.com]

I am hoping to use the banding and striping to make unique items that
set themselves apart from ordinary everyday plastic parts, and not try
to smooth them. Some of the printed things I've seen have awesome
surface textures. Maybe I'm just backward thinking. I don't even have
my Replicator yet.

[Andrew Russell]

Akronqu, interesting point.
I enjoy some of the patterns the print layers produce as as well.
I am also waiting for my replicator, so I haven't been able to experiment.
I'm hoping that I'll be able to manipulate the skeinforge settings (as
well as the geometry I export as STL) in a way that allows me to
control (or at least influence) these patterns.

I'm wondering if there are any direct g-code manipulation tools out there.
The best I've seen so far is a plugin for blender which visualizes the
gcode in 3d.
I don't think it allows for manipulation+export.
I'd love to be able to adjust these patterns for large flat polygon
surfaces to create specific patterns.

[Ian Johnson]

I've gotten PLA to shine up with a heat gun, but it took a long time.
The trick would be melting the surface just enough to smooth out, but
not enough for it to deform.

For ABS I have been sanding it with rough paper to get the lines worn
down maybe halfway or more, and then pouring acetone over it. Dipping
can be hard, because you have to hold it somewhere. I have been
placing parts on a cooling rack over a short pitcher, and then pouring
acetone over it from a cup. Pour the acetone from the pitcher back in
to the cup and repeat. This works better for curved surfaces where
the acetone will flow off of the part. It will puddle on flat
surfaces and develop bubbles as it dries, which leaves pits.

I haven't had much luck making my own slurry, because the plastic I
have been using seems to have some other components which don't
dissolve and leaves it lumpy. Instead I get pipe cement from the
hardware store, made for joining ABS drain pipes (usually black) and
thin it with acetone. It can be tricky to use. I find that if it is
thick enough to fill in the layers, it can be hard to get an even coat
without runs, bubbles or brush marks.

It's best to get the part as smooth as you can before starting on the
acetone. If you use it to make a textured surface smooth, it will
need to melt the plastic enough to also smooth corners, reduce detail,
and soften it enough for you to accidentally bend it or turn it into a
blob. If all you need to do is turn a matte finish to gloss, then a
couple washes will do it. It doesn't save you from sanding, but it
does let you do everything at a rough grit rather than working through
finer and finer sandpapers.

Finishing can be a pain, so I try to compare it to woodworking. Just
because you have planed, cut, and glued the wood together it doesn't
mean you are done. The printer is my workshop's main power tool, not
a magical machine that spits out finished projects.

[Joseph Chiu]

Another suggestion -- from an art/design school friend of mine who
used to make product mock ups with a Dimension printer: use spackling,
sand smooth, then paint.

[Andy]

Good advice, thanks!

Im curious to see how using a dissolvable support structure will affect the surface quality.
If you encase the entire pla surface with a dissolvable structure, I wonder if it can help reduce the visibility of grooves.

-Andy

[akr...@yahoo.com]

I'm still looking myself to be able to manipulate the gcode. The best
I've come up with to put doodles on the top is to extrude them with a
height of one z layer.

-Andy

[Whosawhatsis]

You could also subtract them from the top surface in very thin lines, so that the slicer will have to draw perimeters around the voids.

[Bryan Gardner]

I actually found something on Thingiverse once that might help with ABS smoothing.  It is a stand you make out of PLA, you put it in a coffee can of Acetone, since it is not Acetone soluble the set your ABS parts on it, the fumes from the Acetone will smooth out the rough lines from the print, but not dissolve the object.