Re: PLA vs. ABS

[Barry Schuler]

People will be able to provide a more useful answer if you can talk about what you will be using the printer for. Real parts? prototypes? Architectural models? Also the general sizes of parts: will you be going big as much as possible, or smaller parts.

ABS has been the standard for the last few years in the new generation of FDM machines like Makerbot. It is the material Legos are made of and is tough yet easily dissolved with acetone. It is notoriously finicky to print with, working best on a heated platform.  Large parts are difficult to build as there is a tendency to warp and split during the build process.  All of this can be dealt with via care and diligence in the work process. ABS is available in a great supply of colors.

PLA, which is derived from starchy plants and considered to be biodegradable, has been more aggressively put into use in the last year or so by Makerbot in particular. In general it is more print-friendly, sticks to an unheated platform well and builds without warping. Very large prints are easily done. Virtually every very large 3D printed model you see from MB is PLA. PLA has some temperamental thermal and fluid dynamic properties which led to clogging and flow headaches in machines designed to extrude ABS.  Makerbot decided to optimize and tune the Replicator2 to PLA with the goal of making it easier to print a wide range of models. Based on my experience they have succeeded very well. I have several printers from different manufacturers and print with PLA 90% of the time. Currently, there is less of a variety of colors of PLA and a bit of a shortage in the market.  

That is just a thumbnail - you are likely to get more and varied views and the more detail you can provide, the better help you can get.

On Thursday, November 29, 2012 12:15:50 AM UTC-8, bogus wrote:

Hey all,

my company is considering buying a Replicator 2. Now we don't exactly know the pros and cons of the two materials and therefore we don't know if it's better to buy the PLA based Rep2 or wait for the ABS Rep2X to be released.
Maybe you can list up some pro and cons from your experience and recommend something. That would be awesome.

Thanks in advance!

[Jetguy]

ABS, the same plastic the dash and plastic parts most of your car is
made of. Durable, flexible, and heat resistant. ABS has one huge
downfall; it has a higher rate of expansion/contraction based on
temperature. So when we print with it at 220C and then it cools to
room temp 28C, in undergoes shrinkage. As we print in tiny layers,
this means each layer attempts to shrink and thus curl the part
upwards. This is why ABS pretty much must have a heated bed, to keep
the layers warmer and let the object cool as one mass. Otherwise, you
are restricted to very small parts that simply aren't affected as
much. Simply put, you MUST have a heated bed.

PLA is an entirely different animal. It begins what we call glass
transition (you know that glass is a form of liquid?) as low as
80-100C where it begins to loose its rigidity. In other words, it's
soft, but not exactly melted yet. It melts into a very runny liquid at
around 180C. These properties allow for extremely low layer heights
since the viscosity of the liquid melted form is easy to lay in super
thin layers. The downside is, it requires active cooling blowing on
the printed part to bring it lower than the glass transition
temperature. Basically, you can touch a printed PLA part and it's
still soft for a while if not cooled. It doesn't require a heated bed
and can be printed on top of painters tape or even glass surface when
prepared. It will also stick well to a heated bed with Kapton tape,
but at much lower temps than ABS, as I use 75-80C for the heated bed
VS the 100-110 bed for ABS. This is why you can have a machine that
prints both, with just changing some temperature settings.

Now, the other kicker that MBI is not telling you. PLA will drip from
a standard printhead like the MK7/8 even when not printing if the head
is hot. There is not a good way around this. Thus, dual heads with PLA
is a dream, but not a reality. Sure, you can try it, but you will get
drips everywhere. At the same time, MBI has screwed up yet again and
used the wrong connector for the job on the heated bed of the
Replicator1 (same issue before on the T-O-M). The connector is not
rated for the current and will fail on every single one of them. It
has and is happening here in the forum. It's not if it fails, it's
when.

Thus, the easy fix was to ship the Replicator2 in PLA format only with
no heated bed and no second extruder. This means with a Rep2,
realistically, you can only print in PLA, and only with a single
head.

There are the reasons why I never "upgraded" (cough, cough) to a
Replicator, let alone a Replicator 2. In fact, so much so, I'm working
with the designers of this machine http://typeamachines.com/ and
building a middle of the road alternative documented here
http://www.thingiverse.com/thing:35372

All I'm trying to do is give you an informed point of view on the
Replicator2. It's a fine machine in most regards and will print
extremely well in PLA. It doesn't do ABS since there is no heated bed,
and being the same plastic arms from a Replicator 1 are used, thus, a
heated bed hasn't been tried. Guys who have measured the sag on those
arms from heating have shown about 0.45mm or larger height change,
which is bigger than the nozzle. That means a full thread width of
change is lost and you will see that in a print. There are some fixes
up on Thingiverse if you had a laser cutter. Again, as Replicator2 is
shipped, no heated bed and no problem with sag. It's decidedly a PLA
only machine and due to issues with PLA dripping in a dual head, not
likely to see many conversions to dual head use. If you want ABS or
Dual head use, then Replicator1 is your machine, but it has some known
issues that aren't exactly addressed out of the box either.

The Type A Machines Series 1 printer I linked in its current state is
PLA only too, but I have shown an extensive modification to both 3mm
and 1.7mm filament extruders, PLA or ABS, heated bed, and not
experiencing issues like platform sag with temperature change. It will
also support dual extruders, and I'm actively modifying extruders and
getting close to a no-drip PLA solution. Basically, what I'm saying
is, MakerBot printers are very nice, but there isn't a perfect printer
out there yet. We know what the issues are and there are fixes out
there. You must have some basic skills such as soldering and
mechanical ability to undertake some of the mods. My entire printer is
a mod, and really for more advanced users. Type A has pledged to
incorporate modifications into their units they are selling, but they
also have their own ideas that may not line up with mine, and further,
I'm using MakerBot electronics because the latest firmware named
Sailfish is what only runs on MBI electronics is not really an option
for anyone but MakerBot. Sailfish has not yet ported to other open
source electronics platforms (kind of why this is discussed in the
MakerBot forum), and thus, the Type A Machines and others do not
support it natively.

To me, there is a clear advantage of going with a MakerBot based
machine, and that is this community. The Sailfish firmware is a
testament to that. I think a lot of us have devoted hundreds of hours
and thousands of dollars into keeping upgrades and fixes bleeding edge
for all MakerBot based printers, to even include the Cupcake. The
gripe is, MakerBot might release upgrades to fix some of these issues,
or they may leave them alone. The same thread discussing the upgraded
arms to prevent sag, the new "upgraded" arms still sag. I cannot
recommend you buy a Replicator2, if your intention is that one day, a
heated bed would be released. I also wouldn't hold my breath on the
idea of printing in PLA with dual extruders. The dual headed
Replicator might fix all the problems, but since Makerbot develops in
a complete vacuum and no source is being released, nobody knows but
them (I say shooting themselves in the foot).

Also, the Replicator 1 is a good machine. It might seem like I'm
trashing it, but I just wanted to point out the known issues, rather
than just recommending it like there's nothing wrong. Many people use
it every day and it is one of the few dual head machines in the
market. The heated bed isn't perfect, but does work. MakerBot does
have great support and has fixed many peoples bots and supplied
replacement parts. I just feel you shouldn't be running into a need to
replace some of them ever, but hey, at least you know what might fail.
Again, I actually encourage you to buy MakerBot and enjoy the support
of the community. Just be aware that no printer is perfect, not even
my own. It's all about knowing the limitations and tradeoffs and
making an informed decision.

[Cymon]

Is it just me or has this question been asked a lot.

Like, this week.

[bogus]

Wow thats a lot of information. Thanks a lot guys! Well appreciated.

Actually the size of objects we'll print will differ. We will print product design mockups for ergonomic testing and general surface evaluation. We are more about having precise printouts without to much irregularities in the layer structure (layer splits because of drips and the like).

Thanks again!

[Jetguy]

Well, generally, PLA is the best material for large objects since it
can be nearly warp free when compared to ABS. Even on a high end
commercial printer, really large ABS objects present a real problem.

In that case, a Replicator 2 might fit the bill.

[jhro...@edenenergyworks.com]

Well, I just received a Replicator 2 and printed several parts which were 3" in diameter at the base on a raft with no problem.
But I tried on which was 6" in diameter and the raft curled up so bad that I could not complete the part.

So, why do you say that PLA is not a problem for the Replicator 2?

[Mark Cohen]

I your build platform is not level then things don't stick. When you
went from 3 inch to 6 inch you got closer to the edge of the platform
and perhaps those edges are not as level as the middle of the
platform.

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[Wingcommander whpthomas]

Really large parts printed in PLA may not warp or crank, but the thermal stresses in the part will cause them to bow somewhat. Over 280mm maybe by as much as 1mm. This is pretty easy to correct by dipping the part in boiling water to raise its temperature up to the glass transition and then gently clamping it a flat surface and allowing it to cool.

PLA is not without its challenges, but from what I have seen it is better at large objects, but don't expect a plug and play experience - you will need to understand the limits and strengths of the material and how to tweak it to get the results you want;