This is my attempt of showing you what 3D printing is all about. While the general public can only awe at the thought of what a 3D printer can make and drool over technology that they believe that they have to pay $1K+ just to have one, what they do not know is that such 3D printers can be built by the typical at home user with basic tools for a budget of around $400 USD.[UPDATE: Prices have dropped dramatically since my build. The price of components have now dropped dramatically and building printers can vary widely depending on online prices. Prices mentioned throughout this project documentation should not be taken as the current prices.]
The general concept of the 3d printer can be summarized by one word, ‘layers’. The concept behind the 3D printer and its ability to create solid 3D objects by just extruding lines lays behind the concept that all 3D objects can be “sliced” into 2D shapes. For those who have taken calculus before, this concept may be familiar to them as integrals. Similar to a Riemann sum that is used to approximate the area under a curve, a 3D object can similarly be approximated by its “derivative”, 2D shapes.
As seen on the diagram on the left, the top left picture is a side view of a semi-sphere. On the top right, is a picture of how that semi-sphere is sliced up when being printed. From the top view, these “slices” would appear as circles.
From this view, you can clearly see how a 3D sphere is broken down into 2D circles assuming those disks have an reasonably small width (more on the width later).
As humans, we always perceive one dimension less than what we actually live in. For example, we as humans, live and experience 3D space, yet we perceive our surroundings as 2D. When looking at a sphere, we technically only see a circle. But because of details such as shadow and lighting, our human brains allow us to interpret this 2D image as a 3D object thus automatically adding that extra dimension. Much like the human perception, in order to create 3D objects, a 3D printer creates 3D objects by creating objects 1D lower than the intended product and thus it creates 2D objects. By stacking 2D objects, the 3D printer is able to create a 3D object.
Essentially what a 3D printer does is:
1. Melt and extrude filament that is made from ABS or PLA
2. Draw the first layer as a slice
3. Continue drawing the different layers
4. Those layers eventually build up into a 3D object
For those who are visually unimaginative:
Modules of a 3D Printer
3 Axis Actuation (x,y,z)
A 3D printer’s name itself has the term ‘3D’ which stands for three dimensional. In order to create something in three dimensional space, the 3D printer must be able to move in each of the 3 dimensions. A similar analogy would be (or lack of), would be a car trying to fly when, in reality, it can only move forward, backward, left and right. Because a car lacks the ability to move in the Z axis, it cannot be classified as such.
The 3 axes of a 3D printer are actuated through the use of motors, and structures with tight tolerances. In the case of the Prusa i3, the motors are combined with belts, pulleys, and rods (smooth and threaded) to allow for indirect movement. In direct movement, as opposed to direct movement, is advantageous in the sense that the expandability of an indirect method of actuation allows for the printer to be bigger and faster.
In most 3D printers, the motors are a very crucial component of the specifications of the printer itself because the type of motor as well as the specifications of the motors alone can solely determine whether a 3D printer is a high-end printer or a low-end and thus a low resolution printer. For motors, there are two general types of motors; servos and direct current motors.
The main difference between servo motors and dc motors is the fact that servo motors have a positional accuracy while dc motors do not. DC motors only have two wires that allow it to have only two states, on and off. Servo motors usually have more than two simple power and ground wires (depending on the number of phases and accuracy of the servo motor). A DC motor only has two states, on and off and their speed changes as the load (torque on the motor axle) changes, which, to a 3D printer, is useless because what use is a 3D printer if it cannot print objects accurately just because the power levels fluctuate or the bearing’s friction increase over time. Servo motors, ironically, consist of a geared down DC motor and a positional sensing device such as a potentiometer. By using the positional sensing device, the servo becomes a closed loop system (a self adjusting system) by compensating for over and under- shoots from the intended positions. For this reason, servo motors are used in 3D printers due to their accuracy and ability to compensate for different environmental factors such as resistance and stress.
Rods and Pulley System
Aside from the motors, the rods and pulleys are essential to the build of a 3D printer. For the purposes of the i3, smooth tooling rods and threaded rods are used to control and guide the movement of the three axes. Smooth tooling rods are rods made from heat treated metal to guarantee that they are harder than the metal ball bearings or bronze bushings used to reduce friction between the platforms that the rods support and the rods themselves. The tooling rods are made with high precision so that they are as straight as possible with very little variation in diameter along the length of the rod. Tooling rods are used in the DIY 3D printer scene for their tight tolerances and their resistance to wear from bearings and bushings: qualities needed for a high quality 3D printer that will last the user for a good while. The threaded rods themselves are nothing special in the sense that they can be bought off the shelf from most hardware stores. Threaded rods are used for the printer’s z axis by coupling them directly the motor shafts of the servos. The threaded rods act as a geared down linear motion which is needed for high accuracy layer heights of prints.
The extruder is the main component of what makes a 3D printer a “3D printer”; without the extruder, the 3D printer is nothing more than a under powered CNC machine. In this post for simplicity sake, I will only discuss two main types of extruders; the bowden extruder and the direct drive extruder. All extruders are composed of three main components, a motor, a filament gear, and a hot end. The motor can be any motor as described above but stepper motors are preferred as the number of steps/mm can be controlled via code. (For some builds, people do use DC motors but such builds are usually controlled with very specific hardware that uses PWM to control the power of the DC motor). The filament gear is a piece of machined metal that attaches the the motor shaft. The filament gear has sharp teeth around the circumference with a slight depression to grip the filament. (Description of filament is typical of the MK7-8 series of filament drives that Makerbot Industries have come out with. Cheaper alternatives do not have a grove and are very much just a gear attached to the motor shaft)
Hot ends are setups attached to the filament drive and motor that actually melt the plastic filament being pushed into the hot zone and then out of the nozzle. The hot end setup is controlled by three main components, the nozzle, cartridge heater, and thermistor. (Most common hot end setups) The nozzle serves as the “hot zone” that pushes the melted plastic out.
The nozzle is heated up by the cartridge heater which is essentially a wire of high resistance inside a metal sheath. The concept is very similar to a light bulb filament, the wire is able to get to high temperatures without breaking down when power is inputted. The heater cartridges are usually ceramic because ceramic devices are able to withstand high temperatures. The cartridge has two wire leads which are purely for input only. The fact that there are only two wires means that, like the DC motor, the heater cartridge can only be on or off.
Because the heater cartridge only has two states; on and off, a thermistor is used as a “feedback” device to measure how hot the heater block is getting. Much like the servo’s closed loop functionality, the heater cartridge’s on and off times are controlled via software based on the feed back from the thermistor.
The direct drive extruder is, as the name implies, a system where the filament is drawn by a modified gear connected directly to the motor shaft and then fed directly to the hot end. Such units are usually very compact and can be seen on my previous configuration of my printer. The advantages of such system are that the distance between the filament gear and the hot end is very small and thus there are usually very little complications with the setup and running of. A big disadvantage is that because of its compact-ness, the system has a lot of mass on a moving part of the printer that is being pulled only by pulleys and belts. With so much mass on the moving head, the head has a lot of inertia and thus positional accuracy of the extruder can be compromised at higher speeds due to the tendency of the extruder to continue in one direction when moving.
Link ref: http://clayshieh.com/2014/02/extruder/
On my current build, I have recently changed my extruder setup to a more popular but finicky form, a bowden setup. A bowden setup is a hotend setup where the filament gear and motor setup is separate and away from the hotend setup. Because the motor constitutes most of the mass which causes the inertial problem with the compact setup, the motor and filament gear is located away from the moving head so that the printer is able to print at much higher speeds without worrying about the printer head over shooting and thus leading to inaccurate prints.
There are two main types of filaments used in 3D printing; ABS and PLA. Althought many new filaments have and are being developed, these two remain the most popular by far as they are much more available and there exists more documentation on how to use those two filaments. ABS (Acrylonitrile Butadiene Styrene) is the same plastic used in Legos while PLA is a synthetic polyester derived from plant sugars thus making it biodegradable (over the span of months, using industrial composting methods). Qualitatively from personal experience, ABS is more durable and is more suitable for making components as it is more pliable in its extruded state and holds up well to heat at about 200 degrees Celsius without losing structural integrity, thus “stronger”. PLA on the other hand is a bit more brittle and is affected severely by heat in its extruded form in the sense that it can deform when left in a car on a sunny day. However, although ABS may sound more appealing, ABS has a problem of warping when printing thus often leading to deformed prints or prints that are smaller than intended while PLA does not shrink when printing and thus gives very accurate prints. That being said, both materials are great materials to print with but each to different applications.
The bed is the area where the object is printed on. There are two types of beds/platforms for printing; heated and non heated. Heated beds are essentially PCB’s that have a trace that zig zags the entire surface. The traces are wires but because wire naturally has some resistance, then heat is generated when current is run through the wires that are embedded in the surface. Like the hotend setup, the heated bed only has two states; on and off. So much like the hot end setup, the heated bed also needs a thermistor to provide feedback to the hardware that controls all power outputs. A heated bed is typically used if the printer prints with ABS because in order to make the first layer of ABS stick to the surface, the said surface needs to be hot as well so that the filament coming out of the hotend does not just form a cool side and warp instantly.
If ABS is not used in the printer and the printer only prints with PLA, then a heated bed is not required. For PLA-only printers, the bed is typically a machined surface with glass attached to it to keep the surface flat and true. To provide the filament a better grip of the surface, most people use masking tape to create a textured surface. In some setups, specifically Afinia 3D printers, they use a perforated surface to price the extra surface area as the extruded filaments sinks into the holes and thus gripping to the surface better (a little too well in my opinion).
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