Printer and Movement Styles
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3D printing, sometimes called Additive Manufacturing (because it adds material, as opposed to, say, milling it away) is a diverse field, spanning a broad range of technologies and capabilities. We explore the different styles, and their advantages and setbacks on this page.
Consumer Level Machines
At the consumer level machines are split into two main types, those that use plastic filament and those that use photo-polymer resin.
The filament kind are referred to as FDM/FFM (Fused Deposition Modeling/Fused Filament Fabrication -technically FDM is trademarked by Stratasys but it's the common verbiage)and work rather like a hot glue gun that moves around, extruding plastic while moving to coordinates, usually layer by layer.
Generally, these printers are better suited to functional parts, and larger objects.
Some common printer styles in this category include:
Bedslingers/i3 based (Prusa i3, Ender 3, Taz 6, etc) These printers have a print bed that moves horizontally in one direction (usually called the 'Y' direction) and a nozzle that moves in the other two directions (the other horizontal direction; 'X', and up and down vertically; 'Z'). These printers are generally easy to service and upgrade as their moving parts are generally more exposed and simpler than other styles. Furthermore, they have fewer parts and can be more affordable for the quality of parts used. However, as the movement of the bed creates inertia, often causing 'ringing' at higher speeds. This effect gets worse with larger, heavier print beds, which is why bedslinger styled printers are often considered not ideal for large format printers.
- A subset of this style is the cantilever styled printers, such as the Printrbot series or the Creality Ender 2 - these are generally suited for smaller build volume printers because the weight of the cantilevered arm can bend the arm if it becomes too long.
Delta (Kossel, Rostock, etc) These printers use three simultaneously moving arms to position the nozzle and have a stationary bed. They are capable of much higher speeds than bedslingers, without sacrificing on quality, as the print head is lighter and simultaneously driven by three motors. They do have drawbacks however: due to the complex kinematics, calibration and troubleshooting are far more difficult. In addition, their kinematics inherently result in varying resolution across the area of the build volume, with higher resolution towards the centers and lower resolution towards the edges.
Box-styled/Z-bed printers (Ultimaker, Hypercube, Zortrax, etc) These systems move the print head on the flat XY axis, usually positioning the XY gantry at the top of the printer. The bed only moves in the Z direction, and drops down as the print progresses. These printers are generally more stable and solid than bedslingers due to their boxy frames, and are capable of higher speeds while maintaining quality because the lightweight print head is moving on both fast axes (XY), and the heavier bed only moves on the slow Z axis. Furthermore, their boxy frames make them easier to enclose for printing ABS or higher temperature materials. However, they usually carry more complex mechanics than bedslingers, and require more material to construct the boxy frame: as a result, they tend to be more expensive for the same level of printer, and require more expertise to construct and troubleshoot.
- A closely related style to this category is the XYZ print head/stationary bed printer, which (as its name implies) moves the print head on all three axes and leaves the bed fully stationary. The only prominent printer using this style is the Voron 2 CoreXY, which accomplishes this by moving the print head on an XY gantry and moving the entire gantry on the Z axis. This style is the most complex and expensive out of all of the common styles, but allows for otherwise impossible features such as leveling the gantry with the bed rather than requiring manual bed leveling.
There are plenty of other printer styles, such as XY bed/Z head (Makerbot Cupcake, Velleman K8200), YZ bed/X head (Makergear M3), and even some esoteric/novelty designs such as Tripteron (look it up, it's trippy). For the most part you won't encounter them as often, but if done right some of these more unusual styles can be just as effective and practical as the common styles.
A distinction should be made between a printer's construction style and its kinematics, or the set of equations that govern how the printer moves in response to the movement of its motors. The most common kinematic systems are:
Cartesian (Prusa i3, Ultimaker, Replicator 2, etc) The most common kinematic system. Each motor directly controls the motion on one axis of the printer. The vast majority of bedslinger styled printers (including all cantilevered printers), as well as many box styled printers are Cartesian.
Delta This kinematic system ties directly into the Delta printer style, because it's pretty much impossible to build a Delta-kinematic printer without using the Delta construction style, and vice versa. Three motors move simultaneously along vertical axes to position a print equidistant from all three axis carriages.
CoreXY (Hypercube, Voron, D-bot, etc) In a CoreXY kinematic system, the print head is moved along the X and Y axes by two motors simultaneously acting on it, and the third Z axis is controlled directly by its own motor(s). A more in-depth explanation can be found at the CoreXY website. Typically printers of this kinematic system are built in the box-framed/Z-bed style, but it is also possible to build it with a vertically moving gantry such as in the case of the Voron 2. Interestingly, the CoreXY system is kinematically identical to a Cartesian system rotated 45 degrees about the Z axis.
- The most common terminology mistake between kinematics and printer style is when someone uses "CoreXY" to refer to any box-styled printer, including Cartesian printers such as the Ultimaker or the Ender 5. This is not correct: CoreXY explicitly refers to the kinematics of the printer, not the construction style. Not all box-styled printers are CoreXYs, and it's perfectly possible to construct a CoreXY machine that is not box styled at all.
As with printer styles, many other kinematic systems exist such as Polar, SCARA, and even extensions of these common systems such as Delteron or CoreXYZ. Unlike printer styles, most of these uncommon kinematic systems are novelty systems only because they require unusual construction methods, and have little practical value.
The resin style machines build an object by selectively curing resin using light, and build the object (usually up in layers) in this way.
Generally these printers are best suited to detailed, organic shapes such as tabletop minis.
Some examples of printer styles in this category are:
DLP (Digital Light Processing) and layer masking machines basically split up a model into a stack of cross sections and project images of these cross sections into a vat of resin. Where the light is allowed to touch he resin, it cures. This process is repeated for each layer/cross section to form the final, 3D model.
SLA (Stereolothiography) also uses light to cure resin in layers, but uses a laser which moves around to make up the image of each layer.
Industry Style Machines
Industry style machines are even more diverse. Wikipedia has a good run through of them, and a few are spoken about below:
CJM and CJP - Color Jet Modeling/ Color Jet Printing (Full Color Printing). Using a gypsum based powder, layers are spread as thin as a human hair then a binding solution (clear or colored) is applied to fuse layers together every successive layer. Generally no support material is needed for this process and is one of the most popular full color options. Models are excavated, cleaned, and coated in super glue, wax or epoxy depending on the application. Knows as Full Color Sandstone for its sandstone-like texture.
SLS - selective laser sintering or powder methods work by melting a layer of powder until the desired areas clump and fuse together, then a new layer of powder is added and the process repeated; when the print is finished, the part is removed whole from the bin of powder and cleaned. This is what websites like shapeways and i.materilize use. They're a lot more expensive. Machines start near $120K USD
DMLS- Direct Metal Laser Sintering. Identical to SLS but uses metal and is currently one of the most expensive processes out there. Finished parts are 80-90% (roughly) as strong as cast or formed pieces. One of the most expensive types of printing you can get from service bureaus. Machines start near $500k USD and go up quickly to north of $1Million USD
WHAT IS REPRAP?
RepRap stands for replicating rapid prototyper and is all about making self-replicating machines; 3D printers that print 3D printers. It's an open source community of makers developing printing technology. RepRap is a cornerstone of the 3D printing community and their wiki and forums are a great source of information.