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PLA vs ABS

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Sorry, I did search but didnt find any topic on this....

Whats the difference between them and why would you opt to use one over the other??

Thanking you in advance.

 

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Here's a good comparison:

http://www.protoparadigm.com/blog/2013/01/the-difference-between-abs-and-pla-for-3d-printing/

PLA is easier to print, does not smell, is environmentally friendly (not petroleum-based) and can give even finer detail.

ABS is more difficult to works with and smells bad.

ABS does have some benefits, mainly that it can withstand higher temperatures and that it can be vapor polished with acetone to produce a very shiny surface.

Basically.

 

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If PLA gives finer detail, are the surfaces not completely smooth also?

Also is there anything that can be applied to give that shiny plashed finish??

 

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Neither ABS or PLA comes out entirely smooth. The finer you go, the more 'smooth' it'll look, but you'll still get very small layering.

ABS is soluble by acetone, so people have developed a method to bathe the ABS print in an acetone vapour, partially melting the surface so the layers meld into each other creating a smooth shiny surface.

PLA doesn't react the same way to acetone, so the same process won't work.

I just print in PLA, and while I kind of like the surface if printed at around .1mm, you can fill it with putty, and sand it down to get a smooth model finish and then paint it.

 

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Apart from vapour smoothing you can also bond ABS with acetone very easily. I mainly design mechanical parts that often would required lots of support material. By sectioning your model and using push fit joints, in combination with a quick acetone bonds, you can construct large complicated very robust models using no support material. The acetone melts the plastic, and hence the bond is made using the parent material. If the part breaks it won't be because of a poor bond. Although ABS is petroleum based at can be recycled using a filament maker. Therefore all your support material and old designs can be melted down and reused.

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ABS and PLA parts look almost identical. There is no "finer detail" with either one.

I have trouble telling them apart.

The biggest problem with ABS is it shrinks much more than PLA when it cools. This causes all kinds of problems! Some of these problems are fixed with a heated bed. Some parts will require a heated chamber.

The worst thing about PLA is it can't handle temperatures in a hot automobile with windows rolled up in the summer.

 

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The worst thing about PLA is it can't handle temperatures in a hot automobile with windows rolled up in the summer.

 

So at what approximate temperatures would PLA start to deform, or sag etc, in comparison to ABS??

Thank you.

 

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At the glass temperature. For PLA this is 50 to 60C. This is water that is hot but cool enough to put your fingers into. For ABS around 105C. This is a little *above* boiling! So there is a huge difference.

But even when PLA is above 60C it doesn't exactly melt. It's just that if you pick it up it will slowly form to the shape of your fingers. So PLA at 70C sitting on your print bed will be fine - it won't melt - it will stay in it's proper shape. But if you try to pry it off the bed before it cools to 50C it will deform.

Try putting a piece of PLA filament into hot water that you microwaved. Hold it in there for 20 seconds and then pull it out and bend it. This is very informative and will be a useful lesson. It was for me! There is no substitute for actually *feeling* what happens to PLA. The transition is rather sudden. Yet the melt temp is closer to 180C!

 

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Depends how hot and how big the part is and how solid but usually it would be "ruined". If for example it was under a paper back book it would be ruined. Even just sitting on the dash board or on top of the seat - even if it was a simple cube it would likely get ruined. Something like this would probably be fine:

http://www.thingiverse.com/thing:74322

 

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My PLA TomTom mount cliped on the vent grille failed within minutes when I used the heater for the first time. This air is certainly not as hot as the air in car on a hot summer parking lot. I went for ABS, no more failures.

PLA is relaxing stress viscously even at room temperature if constant deformation is applied (or the other way: constant stress will cause ongoing deformation). All type of clamps lose their grip after some time if not designed overly thick (creep is determined by temperature and stress; thicker parts see less stress, as stress is force per area). It may take weeks or monthes, but in the end the stress in PLA relaxes. If loaded only shortly, PLA is comparable strong, just less ductile, but long term loaded slender parts are preferably done with ABS.

ABS has also lower density, if weight is of concern.

 

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