KI7TU's Reference Page - 3-D Printing: An overview and introduction


I'm certainly not a "guru" on 3-D printing, but I do have a 3-D printer and have printed quite a few objects on it. (I first got it in early 2015.) I've also published a few designs.

This page is based on the contents of a presentation that I've put together to give to various clubs. It assumes that you have a "technical bent", but likely little to no background on 3-D printing beyond what you've seen on TV or the like. It's also subject to change, reorganization, and general improvements based on audience comments at the presentations.

The one sentence summary:

3-D printing is the process of making a physical object by building up thin layers of material under computer control.

It sounds a lot more complicated than it is

When you first read through the stuff below, it sounds really complicated. But in reality, once you've done it a few times, it becomes pretty easy. Actually printing an object breaks down into four basic steps:
  1. Getting and preparing the model
  2. Preparing the printer
  3. Actually printing (mostly "hurry up and wait")
  4. Clean up the printer
(Just remember that virtually anything you do, if you start breaking it down into the steps that a "complete newbie" will understand will make the whole sound horribly complex, even if it's just driving over to get a cup of coffee, especially when you have to throw in the background info like "if the traffic light is red, stop and wait for it to turn green".)

Classes of making things

You can break down all processes of actually making things into two general classes (though some ways fall into both classes): additive and subtractive.

An "additive" process is one where material is added to the object being created. One example that you've probably done is making something with modelling clay, where you shape a basic head, then make ears that you stick onto it and so on.

A "subtractive" process is where you start with a big chunk of raw material and start removing parts of it until you have what you want. The classic example of this is a sculptor starting with a piece of stone and "removing everything that doesn't look like an elephant", in order to create an elephant.

Some examples of subtractive techiques would include: Some examples of additive techniques would include: It's worth noting that many, if not most, actual items are produced by a combination of subtractive and additive techniques. For instance, a craftsman making a cabinet will use some subractive techniques, such as sawing, planing, and drilling, to prepare the pieces, then use additive techniques such as gluing parts together and connecting the hinges to the wooden parts with screws.

It's also worth noting that some techniques, such as molding or casting, can be seen as either additive or subtractive, depending on your view point.

3-D printers are about as additive a process as it gets. They start with an empty build platform, and start adding material one thin layer at a time.

Types of 3-D printers

There are basically 3 types of 3-D printers, though there are also some other more exotic ones. (There may be others that I'm not aware of!)

Sintered metal printers

These printers take a powdered metal, and use a high powered laser to melt it a bit so that it sticks together. (This process is called sintering.)

The process of sintering has been around, as far as I know, since the late 19th century, and is used to produce bronze bearings for motors and engines. One of the advantages to it is that it does not produce a solid part, the way casting does, as the metal isn't fully melted. For bearings, this porosity of the part is good for getting lubrication (e.g., oil) to the contact points.

The sintered metal 3-D printers have added computer control, using lasers to do the melting. Typically the part will be lowered in the powder as it is printed.

Sintered metal 3-D printers are well beyond the average hobyist, with costs on the order of $50,000 and up. (Mostly up!)

Liquid immersion printers

There are materials (mostly plastic emulsions) that are liquid, but when struck by light of a certain wavelength, become solid. Often a laser is used to provide the light.

This property is put to use by having a computer-controlled laser, and an arrangement to lower a print bed into a bath of the liquid.

This method of 3-D printing has some advantages, but it also has some drawbacks. One of the major drawbacks is that you have to have enough of the liquid on hand to fill the print chamber to at least the height of the object to be printed. Another is that, being a liquid, unwanted raw material can pose a disposal problem.

There are a few "hobbyist" grade liquid immersion printers around, starting at around $1,000. The liquid for them is not as readily available as for the fused filament printers. There are also commercial grade liquid immersion printers, and the ones I've seen start at around $30,000.

Fused filament printers

These 3-D printers take a filament, which looks vaguely like a very heavy fishing line or the "string" for a string trimmer (also known as a "weed whacker"). The printer melts the filament, and moves the tip and/or the print bed around, depositing the molten plastic directly onto the bed or the layer of plastic previously printed. (If you're not aware of it, one of the meanings of the word "fused" is "melted".) The newly deposited layer melts the top of the layer beneath it, causng them to weld together.

Once all of the plastic in one layer is deposited, then either the print bed is lowered, or the print head is raised, and the process repeated for the next layer.

The motions of the print bed and/or the print head can be controlled to a small fraction of an inch. However, it's usually possible to see the layering in a printed object, unless other steps have been taken to smooth the surface.

The vast majority of "hobbyist" 3-D printers, as well as most of the commercial-grade printers, are fused filament printers. They can range in price for a few hundred dollars for small hobbyist printers, up to $50,000 (or more) for commercial-grade printers.

The raw materials, the filaments, are readily available in most larger cities, as well as from many on-line suppliers. They are available in a wide variety of both colors and types of plastic.

Other types of printers

I should mention that there are other, more specialized printers. They can use a variety of techniques to deposit the layers. I've heard about 3-D printers that print wax objects for use in lost-wax metal casting. I've also heard about ones that print in a fine plaster and are used by archaeologists to make copies of fossilized bones, or to produce replicas for missing bones in a skeleton.

The rest of this section is going to concern itself with fused filament printers.


As I mentioned above, the filaments resemble very heavy fishing line or the "string" for yard string trimmers. Older printers use filament that is 3mm in diameter, but newer printers have gone to 1.75mm diameter filament.

Filament is generally sold by weight, usually in kilogram or half kilogram rolls, though others are sometimes available.

There is really quite a variety of filaments available. Naming a few:
Most of these come in a variety of colors. Some are also with a "filler", such as wood chips or powdered metal. There's at least one that's electrically conductive (although it has fairly high resistivity).

Each of them has their own special requirements, advantages, and problems. For instance, ABS tends to give off a bad smell while it's being printed. PLA can start to get soft around 50°C (122°F), which can be a problem if left in a car in Phoenix. Most of the filaments can absorb moisture from the air, causing problems when it gets heated well over the boiling point of water. In general, it's wise to take steps to protect one's supply of filament from humidity, especially when it's not actually being used.

Some, such as ABS or PLA, can be had for $20 to $30 a kilo. Others, such as Ninja Flex® can cost as much as $50 for a half-kilo.

3-D Computer models

Before a computer can build a 3-D object, it has to have a "picture in its mind" of what it is going to build. We call this picture a "model". (Note that it actually has to be a 3-D picture, not just a flat snapshot.)

This picture, or model, can take several different forms. It can be a surface, usually represented by a mesh of small triangles or other shapes, of the object. One way to think about this is to have a mental image of what the object would look like if a pantyhose leg were slipped over it and stretched tight. This can be done for any arbitrary three dimensional shape.

Another form for a model is to have one or more (usually many more) basic shapes, such as cubes, cylinders, pyramids, and so on, that are assembled to make a larger object. The shapes can also be what is referred to by the fancy term "negative space" which just means describing a hole where ever it intersects with another basic shape which is not negative space. (Thus we might have a cube with a cylindrical hole through it.) This type of model is sometimes referred to as a parametric model, because it is fully described by the parameters of the various basic shapes that make it up.

Getting a 3-D model


One way to get a model into a computer is to use a 3-D scanner and scan an existing object. This can work well when you already have an existing object and want to use a 3-D printer to make a copy of it. The downsides include the cost of the 3-D scanner (which sometimes is more expensive than the 3-D printer), and the fact that you have to actually have the original of the object.


There are a number of CAD (Computer Aided Design) programs around that can be used for designing 3 dimensional objects.

Some of these are intended mainly for use by artists, and often times include features for animation.

Some of these programs are more intended for doing things like designing parts for small machines, or designing playing pieces for games. In many of them you create drawings, and by actions such as extrusion or rotation, you create a three dimensional object. There is at least one of them (OpenSCAD) that you actually write a "program" that parametrically details the final object.

Once you have designed a solid model in any of these, you export a mesh file (usually with the file type ".STL") for use in the next step in the process.

The prices range from free (for open source programs such as
FreeCAD or OpenSCAD, to tens of thousands of dollars per year of license. Some of the commercial programs do have a "free hobbyist" version that is limited in what it can do. Also, there are some "on-line" design programs available.


Many people (myself included) are willing to share their designs by posting them to one of the many repositories.

The one I like best is Thingiverse. That's where I post mine. As far as I know, they don't let people charge for downloading their designs (though the person posting it may prohibit you from selling objects made from their design). Every day there are dozens of new designs posted on Thingiverse (go to Explore and select Things to see the newest first).

There are some other repositories that allow people to charge for their designs.

Slicing the model

Having a 3-D "picture" of what you want to print, in the form of a mesh file (usually a ".STL" file) is nice, but 3-D printers can't directly make it from that. For one thing, the mesh file very well may start at the top, when the 3-D printer needs to start at the bottom. Also, the mesh file only includes information about what the surface of the object is like, and it (usually) does not include information about what's "inside the solid parts".

There is a process to convert the model to something that the 3-D printer can actually use. It's called a "slicer", or "quot;slicing program". The name comes from the idea that the 3-D printer builds up the object using fine slices, sort of the way a cook might build a sandwich. There are a number of slicing programs available. To name a few: There are several others. For what it's worth, I normally use Cura.

The slicer programs prepare what is called a "gcode" file. The gcode is an extension of an older standard for controlling things like milling machines. It includes things like setting the temperatures that the 3-D printer uses, moving the printhead around (usually after calibrating it to the print bed), and when and how fast to feed the filament.

The slicer program also deals with the "infill" for "solid" portions of the object. To conserve both materials and time, the slicer program is capable of doing a sort of "honeycomb" structure within the "solid" portions. The user can specify a percentage infill, from 0% (empty) to 100% (solid). Parts that have higher mechanical stress, and thus need more strength, can be printed at higher fill levels.

Printing the model

Once the "gcode" has been generated, you need to actually get it to the printer, and have it print it. There are also some steps that (sometimes) need to be taken to prepare the printer, but I'll mention those later.

There are basically three ways that you can do this, depending on which printer you actually have:

Using your main computer

Although this is the least expensive (at least at the start), it does tie up your computer and you may have problems doing other tasks while running the 3-D printer. Since large prints can take several hours, that can be a problem.

Also note that the 3-D printer can introduce large amounds of vibrations and shocks into the table that it's on, and if you try to use the typical general purpose computer and have it on the same table, you may soon have problems induced by the vibrations and physical shocks.

Some slicing programs, such as Cura, can actually send the gcode to the printer while it's being generated, rather than sending it to a file.

Controller built into printer

Some (many) higher-end 3-D printers include a controller computer that has a nice LCD display screen, and some user-interface controls. You download the gcode file to the printer, via a USB connection, a memory card or stick, or possibly a WiFi connection. You use the controls to select which file you want to print, as well as some other possible prarameters to control (such as adjusting the temperatures the printer will use).

Separate Single Board Computer as controller

You can use a Single Board Computer, such as a Raspberry Pi, to control your 3-D printer. One good program to do this is called
OctoPrint. You can then talk to the Raspberry Pi via either ethernet or WiFi, and it controls the printer. Once it's set up, you can use any device that has a web browser (that can get into your local network) to actually control the printer.

If you have an older "Model B" Raspberry Pi sitting around, this is a good use for it, as OctoPrint will run quite happily on it. (By the way, this is the setup that I use, as I happened to have a spare Model B that was not doing anything.)

Common problems in printing the model

There are many things that can go wrong when actually doing a 3-D print. However, there are generally things that can be done about every problem. (Lots of folks are making lots of 3-D prints, so it's just a matter of fixing what's wrong.) To name a few things that can go wrong: Going into the solutions is beyond the scope of the overview, but I will say that the most common problem I've seen are adhesion problems, that is, getting the object being printed to stick to the print bed. The main things to do about this are to make sure the actual print surface is clean, and that the plastic being printed has a good chance of adhering to it. (For some plastics, this may mean putting a layer of blue painters' tape down, while for others this may mean putting a coating of adhesive down.)

Limitations of 3-D printing

There are several limitations to what can be 3-D printed, though there are also some things that can only be produced by 3-D printing.

Some of the limitations and drawbacks of 3-D printing include: Some of these limitations do have work-arounds.

Time it takes

The time to print an object will often be in the hours, depending on the complexity of the object and how big it is. It also depends somewhat on exactly what type (and even color) of plastic is being printed. (The colorants used in the plastic can affect it's properties, and sometimes this means printing more slowly.) It's also a bad idea to leave the printer alone for very long, as there are many things that can go wrong. At best, they cause a print to be ruined, and may make a horrible mess. At worst, they can cause a fire. (Once you've got it set up correctly, you don't have to watch it every moment, but checking on it every few minutes is a very good idea.)

Due to how long it takes to produce an object, if many copies of the same object are needed, it may be less expensive to make a mold and injection mold the object. It should be noted that making even a simple mold costs several thousand dollars, so this is only economically viable when the number of objects exactly the same design to be made is large. Injection molding machines can generally make several, to even hundreds, of objects per hour (again, depending on both the size and complexity of the object).

While comparing injection molding and 3-D printing, it should be noted that injection molding generally uses pelletized plastic, while 3-D printers generally use an extruded filament (which itself is made from the pelletized plastic). This means that the cost of the actual plastic for 3-D printers is several times that of what's used for injection molding. Also, it's easier to "reuse" plastic (e.g., from objects that didn't come out quite right) for injection molding. (One can get an extruder that accepts the pellets, or ground up bad prints, and makes "new" filament out of them, but the cost of the extruder will exceed what most folks will spend on filament in several years.)

Size limits

About the smallest 3-D printer on the market has a "print space" of 100mm X 100mm X 100mm (about 4 inches on a side). Many printers can do 300mm on a side, and a few can do more than that, though going much beyond that introduces its own problems. It should be noted that there is some "unusable" space on every side of the object being printed. Although this is, to some extent, controlled by the software, it's typically about 5mm to 6mm (roughly 1/4 inch), on each side, or about 10mm to 12mm (a half inch) in every direction that can't be printed.

By comparison, there are injection molding machines that can deal with objects several meters on a side (think large truck parts), though ones this big are few and far between. Much more typical are ones that can do 500mm or so on a side.

Need for physical support

Because the prints are made of layers, every layer (after the first one) needs to have something underneath it. It will work to have an object that expands with height, though as a general rule of thumb the overhang should not exceed 45° of angle. The one exception to this is that it is possible to "span" short distances, usually a very few millimeters, as long as there is support on each end.

Most of the slicer programs are capable of including small support structures in the print, thus allowing it to be printed with a single plastic. After the object is printed, the support sturctures are then either broken off or removed with a knife.

Many professional grade machines, and some hobbyist grade machines, are able to print using two different plastics, intermingling them. One of the plastics is usually selected to be soluable in some solvent (e.g., water) that does not effect the desired plastic. Once the printing is completed, the object is immersed in the solvent to dissolve the supports.

Smoothness of surfaces

Given the fact that the printers work by putting down a series of layers of "threads" of plastic, it's no surprise that the printed surfaces aren't perfectly smooth. However, depending on which plastic you're printing, it is possible to do some "post processing" to make the surface smoother. For instance, if you are using ABS, it is possible to use acetone as a solvent to smooth out the surface.

Multi-color is difficult

Today we're used to having 2-D printers (that print on paper) that can print in "full color". (Actually, this is a bit of an illusion, as they really only print in 3 colors, though they usually also have black ink as much of what gets printed is black.) They work by printing a series of fine dots, and adjusting the amount of the three "primary" colors to get the desired color. Part of the trick is that the dots are so fine that they appear to the eye as a single dot of the resultant color mixture. Today (2015), a 300 dots per inch (DPI) printer is considered to be not all that good.

For a 3-D printer, it's not unusual to lay down the layers at a rate of about 70 or so per inch, or less than a quarter the resolution of even a cheap paper printer. Furthermore, most consumer grade 3-D printers have only a single extruder, though some have two extruders. This means that they can only build a print with one color (or two colors for a dual extruder). While it is theoretically possible to build a printer with three extruders, it would be much more expensive using today's technology. Also, the results would likely be disappointing given the resolution. Although most 3-D printers are capable of higher resolution, the time to actually print the object goes up dramatically. To achieve higher resolution, a tip with a smaller opening needs to be used, meaning many more passes per layer, and many more layers.

Another issue with multiple extruders is that the stepper motor that drives the extruder needs to be actually at the extruder. Most designs for 3-D printers have a movable printhead, meaning that the extruder moves. Having multiple extruders means more mechanical load on the moving mechanism, which creates more demands for a rigid structure, further increasing cost.

I probably should also mention that it is a bit of a hassle to change filaments with today's technology. The extruder has to be brought up to temperature (this can take 10 or so minutes), then the old filament has to be removed, and the new filament fed through the extruder. Steps then need to be taken to clear the old filament from the extruder. The easiest way to do this is to print a small object, like a calibration block (which also verifies some of the other settings of the printer).

This screen last updated: 08-Oct-2015

Copyright © 2015 by Clark Jones