3D Printing FAQ

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AMT 3D Printing FAQ

Yes, 3D printing is all the rage.  There's a lot of great information on the web, and there's a lot of misleading baloney.  Here's our no-nonesense catechism.

What is a 3D printer anyway?

It's a computerized hot glue gun:

  • Instead of glue sticks, it uses filament... a long semi-rigid rod of plastic that comes rolled on a spool.
  • The nozzle is much finer than a glue gun, usually having a 0.4 - 0.5mm diameter hole.
  • It has computerized mechanical gadgetry that moves the nozzle in 3 dimensions, squirting out (depositing) several thin horizontal layers of plastic.
  • Each layer slightly melts onto (fuses to) the previous layer forming a solid piece.

Actually there are many technologies used by 3D printers, and they're rapidly evolving.  We've just described the cheapest, most readily available type using: Fused Deposition Modeling (FDM) or Fused Filament Fabrication technology (these terms are interchangable). 

This guide doesn't go into powder or resin based 3D printers.  They're much more expensive and often produce much higher quality prints.  You can experiment with them through online services like Shapeways.

I just want to print stuff without learning anything at all.  Can I do that?

Well, no.  Just learning to operate the printer requires a certain investment of time, but it's not terribly difficult.  We'll help.  For your first time, see the next question.

I just want to print models I've downloaded from the internet.  Can I do that without learning all that complicated modeling software?

Probably.  It depends on the model you've downloaded.  If you get a proven STL file from Thingiverse or some other 3d-print-focused website, odds are it will simply work without further modification.

If your model is not in STL format, it must be converted.  Open the model in a modeling program, (preferably the one that was used to create it); then 'export' or 'save-as' STL.

Not all STL files will work.  Try running your STL through the slicer (you can do this on your own computer even without a 3D printer).  If it fails, the STL file may be 'non manifold' or have other complications.  (see 'manifold' below).

I want to design my own things to print.  What's involved?

You need to learn to use a 3D modeling program of some sort.  These seem to take one of two perspectives: artistic (i.e. Blender) or engineering (i.e. FreeCAD).  The more powerful they are, the more complex they are to use.  Expect to spend at least a few days to learn the basics, and a lifetime to master.  We have a list of good choices here: Modeling Software for 3D printing.

Be prepared to change your mind if you discover that the program you first selected doesn't fit your needs or temperament.

To print your model, it must be saved or exported as an STL file.  Most modeling programs can do this.  Some modeling programs export STL files that are not suitable for 3D printing without cleanup.  (see 'manifold' below).  If this turns out to be a frequent problem and/or too onerous for your tastes, you might consider using a different modeling program that produces cleaner STL files

Your cleaned up STL file is input to the printing process (below).

What are the steps when it comes to actually printing my thing.

(These are general steps.  For details of our printers, see the 3D printing 101 course material).

Someday, maybe we'll just be able to press 'print' from our modeling software, and the item will start printing on our 3D printers.  We're not there yet; instead there are a few steps:

  • Export your model as an STL file.  If you downloaded from Thingiverse or elsewhere, it may already be in STL format.
  • Process the STL file with 'Slicing' softare.  A slicer figures out how the print head should move, and how much plastic to squirt where.  The software cuts horizontal 'slices' through your model, and traces outlines and fill patterns for each.  Then it creates tool paths from these slices in 'gcode' (usually) or a proprietary variant ('x3g' for MakerBot).  The slicing sofware has lots of settings; but most have reasonable defaults.
  • Set up the printer.  This involves loading filament, cleaning and leveling the bed, replacing any damanged tape on the print bed, etc.  The exact process varies for each printer.
  • Deliver the 'gcode' file to the printer and start the job running. There are two ways to do this: 
    • Connect your computer to the printer via USB and run a program which sends the gcode piece-by-piece.  This program also displays any status or error messages from the printer.  Sometimes the monitor pogram is integrated with the slicing program.
    • Some printers allow you to copy the gcode file to an SD card, to run un-tethered.  This is recommended if possible, as it eliminates the possibility of a failed print due to a computer crash or USB communication failure.
  • Once the print is done, remove it from the build plate and clean up the printer for the next user ('better than you found it' is the AMT way.)
  • If your part uses support material, this must be broken/cut/filed/sanded/ground off.  This is sometimes easy, sometimes a real pain in the neck.  Avoid if possible (see below).

What kind of plastic can I print?  What's it like?

PLA is the material we recommend for getting started.  It's quite rigid and strong; can be easily printed without a heated bed; and emits no noticable fumes while printing.  It's made from renewable resources (cornstarch or tapioca) and is biodegradable.  (Actually we're not sure about the dyes that are used to color it, so please recycle).

The next most common material is ABS.  It was more popular in the early days of FDM printing.  Good quality prints require at least a heated bed; some parts really require a completely enclosed heated chamber.  It stinks when printing. The resulting part is very similar to PLA (just a hair more flexible).  The familiar Lego bricks are made of ABS.

PET has similar properties to ABS but slightly friendlier to use.  No heated bed required.  Turn off the layer fan when printing to avoid warps.

Nylon is much tougher than ABS or PLA.  Similar printing issues to ABS (requires heated bed).

There are lots of new materials coming out all the time.  We recommend you get some experience with PLA before trying them.

I read somewhere that 'my imagination is the only limit...'  Really?  I have a vivid imagination.

Don't buy the marketing baloney.  FDM printing has limits just like any manufacturing process.  You should understand them and have realistic expectations going in.  Plan to learn a lot. The more you learn, the more limits you'll overcome. 

The most basic limit to understand is overhang.  Since parts are built in horizontal layers, there must always be something underneath for each layer to stick to.  The slicing software will not generally warn you about this, and will happily produce a useless pile of miniature plastic spaghetti if you're not careful.

Often, simply re-orienting the part on the build platform will solve an overhang problem.  Sometimes designing the part in separate pieces to be assembled afterward is your best bet.


You can get away with gradual overhangs.  Anything up to about 45 degrees usually works fine; from 45-60 may even work; beyond 60 degrees is usually trouble.


For short distances, you can usually get away with a 'bridge.'   If the filament will be attached on two sides of an overhang, it will stretch across and 'bridge' the gap.  For wider gaps, the filament may sag between the attachment points, but often clears up a few layers later.  You may be able to simply cut or file away the stringy bits after the print.  Using a fan to cool the workpiece while printing can improve bridging.


Structurally, parts are usually weaker along the layer lines than across them.  This is because the fused joints are not as strong as the filaments themselves.  If bending strength is an issue for your part, be aware of this, and perhaps reorient the part when printing.


What is 'support material'?

Another solution to overhang problems is to add 'support' material, designed to be removed and discarded after the print is complete.  You can add support material yourself, as part of the original model; or you can have the slicing software automatically generate support material.  

This can be a tricky problem.  Sometimes auto-generated support works great; sometimes not.  It can also be difficult to remove, and of course it consumes material.  Experiment or talk to a steward if you're unsure.

Dual extrusion printers can use soluable support material, designed to be dissolved or washed away after printing.  This is an advanced technique, and is not supported on any current AMT printers.

What is a 'dual extrusion' printer?  Why would I want one?

A dual extrusion printer has two nozzles, and can be loaded with two different colors or types of plastic.  This is convenient for multi-color printing, of course.

More importantly, it allows the use of 'soluable' material to be used for support during printing.  After printing, the support material is dissolved and washed away.

Dual extrusion printers can be tricky to set up, as the nozzles must be precisely the same height (within a fraction of a millimeter).

We do not have a dual extrusion printer at AMT.

What is a 'manifold' model, and why should I care?

An STL file contains a representation of the surfaces of a 3D object.  To successfully print, the STL must describe surfaces that completely enclose a solid object, but the STL format itself doesn't enforce this.  This is what we mean by a 'manifold' model.  It's most easily understood by example:

Imagine the following paper model, folded up and glued to form a box:


This is a 'manifold' model, and can be successfully printed.

Now imagine that we remove one face of the model like so:


From the front our block looks the same.  If we turn it around, we see the missing surface.  This is a 'non-manifold' model.  It doesn't represent a 'solid' object in the computer's mind.  It can be tricky to spot these because, at first glance we intuitively assume that the missing surface exists.

The concept of 'watertightness' may also help grasp the idea.  The second box would leak if filled with water, therefore it's non-manifold.

Of course, the problems are usually more perplexing.  Here's a block containing an octagonal hole.  Note that the hole has internal surfaces along its length.  If we turn the block slightly and examine all these surfaces, we see that one is missing.  This is enough to prevent successful printing.


Here's an even more devious example.  We aren't missing any surfaces, but if we zoom in and examine closely, we see that two adjacent surfaces don't quite meet at one of the corners.  Water would leak out this slot; it's non-manifold and may fail when printing.


Note that in all the preceeding examples, the models cause no problems if used merely to illustrate a part, as long as we're viewing the good side, or from a sufficient distance.  This is why models exported from 3D illustration software don't always work well for 3D printing.

As models get more complex, this sort of problem can be very difficult to locate and fix.  Tools like Meshlab can ease the task, but they're complex and using them effecively is an art.  It's sometimes easier to fix in the original modeling program and re-export to STL.

Modeling progams that internally represent objects as solids rather than surfaces tend to export STL files with fewer problems.  Keep this in mind when choosing a modeling tool.

You can always bring your model to one of our meetups, and we'll give you a hand with it; or we'll give you the bad news if it's beyond hope.  Bring your laptop if you can.

Do I need to buy CAD or modeling software?

There are several free or open source choices in our Modeling Software for 3D printing list.  Your author is a big proponent of open source software.

What kind of printers do you have at AMT?

Ours are all FDM printers.

What is the biggest thing I can print?

Different printers have different limits.  See the page for each printer in our stable.

If your thing is too big, consider breaking it into pieces for subsequent assembly.  

I want to learn about 3D printing, but I'm not sure I want to join AMT.  Is that OK?

Absolutely.  Our 3D print meetups are all open to the public.  We try to foster community; not make a sales pitch for AMT.  Of course, we can tell you all about AMT too if you're interested.

Do I need to buy my own material to use the AMT printers?

No.  We have a supply of filament at AMT for member use.  If you're working on a huge project, it would be nice to bring your own.  You'll probably want to anyway, just to insure that you don't run out of the color you want, etc.

I want my own 3D printer.  What kind should I get?  How much do they cost?

Consumer 3D printers have become very inexpensive; some for less than $200.00 now.  High-end machines can be well over $2000.00.  Kits at the low end of the spectrum sometimes have a poor manual or none at all... but you'll find friends on the internet.

Kits at the high end might have better support.. but are not necessarily worth the extra expense... it really depends on you and what you're comfortable with.

Come to our meetings and see a 3D printer or two to get ideas.  If you're more technically inclined, you can save money with a more do-it-yourself printer.  If you're not technically inclined, ...read on.

I want a printer that 'just works' without any fiddling around. Should I spend more on a big-name printer?

We have yet to find a truly 'plug and play' printer, but have no difficulty finding manufacturers who will make that claim.

Expect to spend a bit of time learning to use your printer no matter how much money you spend.  More money may get you a nicer printer and high quality technial support, but not necessarily.  If tech support is important to you, search the web for customer comments on the manufacturer you're considering.

Avoid printers that use a proprietary 'filament cartridge'.  We feel this is a sleazy way to lock you in to buying their more expensive filament, without necessarily making anything easier or higher quality.

We've seen printer kits for as little as $150.00.  Sometimes these are incomplete, and they are not likely to come with any technical support; maybe not even an assembly manual.  Then again, if you're thinking about building your own printer anyway, such a kit may be a great way to get started.  (see next question)

If after all that you still want us to just tell you which one to buy, we can recommend the Prusa I3 Mk2 without hesitation.  It's not the cheapest, but it's reasonably priced for what you get.  See this blog post for the reasons we bought one.

I've heard that you can build your own 3D printer... Seriously?  Why on earth would I want to?

Yes, you can do it.  You'll have to learn a few things.  You don't need to be a programmer or electronics whiz; mostly it's a straightforward assembly project.

Why?  There's a great sense of satisfaction of course, and you'll certainly save money.  Thanks to cheap manufacturing in the far east, a top quality 3D printer can be built these days for well under $500.00.  That includes nice features like a heated bed and automatic leveling.

When you're done, you'll be prepared to troubleshoot anything that goes wrong with your printer.

The central website for information on the subject is reprap.org, but there's a lot of information elsewhere as well.  When researching, pay close attention to the age of the content you're reading.  Anything over two years old may be out-of-date, though not necessarily irrelevant.

I bought/built a 3D printer but I can't make it go.  Can you help?

Yes!  Bring it to one of our meetups.  We'll get you going. Examples:

Funky Printerbot
Nifty Delta
AMT-built Prusa
Matt's delta
Inexpensive Prusa kit

Do I need to learn 'gcode' ...or any other programming language?

No.  These are advanced techniques that you may explore if you like, but nothing requires programming or electronics knowledge.

I want to somehow scan or photograph my [sculpture | dog | earrings | ...] and then print a copy on a 3D printer.  How do I do that?

3D scanning is an emerging technology that's getting better all the time.  We don't have a scanner at AMT, but we may explore the idea.  As we learn more about the technology, we'll keep you posted.

Can I print a replacement kidney?

Not quite yet.  As soon as the technology matures, we'll place an order for some kidney-filament :-)


Can I print my own gun?

<sigh>.  Go somewhere else please.

Can I print my own rubber-band gun?

That's better.  Check out a few options here: http://www.thingiverse.com/search?q=rubber+band+gun

What does [extruder | STL | gcode | ...other jargon] mean?

See our 3D printing glossary