Idiot's Guides: 3D Printing (2015)
PART 2
All About the Hardware
CHAPTER 8
The Build Platform
In This Chapter
· Materials commonly used for build platforms
· The purpose of heated beds and build chambers
· Different surface treatments to improve adhesion
When it comes to 3D printers, every part on the machine is important to its functionality. That’s true even for things that seem simple and uncomplicated, like the build platform (also called a print bed or build plate). The build platform is actually just as crucial as any of the other parts and can be just as complicated.
The build platform is where the printer actually deposits the plastic to make the part. This seems straightforward, but in order for the print to be successful, the plastic needs to stick well to the platform. There are a few factors which determine how well the plastic will stick: the flatness of the platform, how level it is, what material the build platform is made of, and any surface treatments which are applied to the platform.
In this chapter, I go through all you need to know about the build platform, including what it’s made of, the various parts that make it up, and the surface treatments used on it to improve adhesion.
Build Platform Materials
There are a handful of materials that are commonly used for build platforms, such as glass, borosilicate, aluminum, and copper. What all of these materials have in common is they can be made very flat. The flatness of the build platform is essential for ensuring the plastic sticks to the bed. This is because the nozzle has to remain at a very specific height above the build platform for the extruded filament to adhere to the bed, and that height wouldn’t remain constant if the platform weren’t flat.
DEFINITION
Borosilicate, also known as Pyrex (one of its trade names), is a type of glass that is formulated to reduce thermal expansion. Because it’s much less prone to thermal expansion than normal glass, it’s at a much lower risk of thermal shock. Thermal shock can crack traditional glass if it’s quickly heated or cooled unevenly, a problem that borosilicate doesn’t experience.
In addition to being flat, the build platform has to be constructed from a material that the molten filament can actually stick to. Some materials are too slick, and the extruded filament simply won’t stick to it. An ideal material would let the filament stick very well while it’s printing, and then allow it to come off easily when the print is done. If it sticks too well after the print is done, it can be difficult to remove the part without damaging it.
For this reason, specialty build platforms are being developed just for 3D printers. This is a brand new type of product, but the selection should increase dramatically in the coming years. The platforms themselves are made from a variety of materials, depending on the particular manufacturer. But the goal is the same for all of them: for the plastic to stick well while printing and come off easily when the print is done. But in many cases, in order for that to work, the build platform needs to be hot. This is where heated beds come in.
Heated Beds
Heated beds, as the name implies, keep material warm. A heated bed works pretty similarly to a hot end in principle: a thermistor measures temperature, while resistive heating is used to get the bed hot. In this case, though, the entire bed is a big resistor that heats up instead of just a small heating element.
Conventional heated beds are large printed circuit boards (PCBs) specifically designed with large copper traces that act as a very low-ohm resistor (due to Ohm’s law). When voltage is applied, this draws a very large amount of current.
A large 12×12-inch PCB used for heating the build platform.
FASCINATING FACT
Recently, other types of heated beds have started to gain popularity in the consumer 3D printing industry. This includes silicone heating pads, which have long been popular in other industries. Unlike traditional PCB heat beds, these are flexible and are manufactured in a wide range of sizes and shapes.
With all of that power flowing through what is basically a resistor, the heated bed gets hot—anywhere from 60°C to 120°C is common. This, in turn, heats up the build platform. And just like with the hot end, the 3D printer monitors the temperature using the thermistor (see Chapter 7) and adjusts the voltage going to the heated bed to keep the temperature steady.
One of the benefits of a heated bed is reduction in the warping of a part. As I covered in earlier chapters, warping happens when the part contracts as the plastic cools. A heated bed can help combat this problem by keeping the part warm as it is being printed. For some materials, like ABS, a heated bed is basically a requirement. Other materials, such as PLA, don’t need a heated bed but can still benefit from one.
This is the reason why some 3D printers include a heated bed and others don’t. Generally, only inexpensive 3D printers come without a heated bed. Those printers can usually only successfully print PLA. In order to print ABS (and many other materials), a heated bed is a necessity.
In addition to reducing warping, heated beds also help filament stick to the build platform. Heating the build platform gives the filament a nice, hot surface to stick onto, which is true for all of the material types on the market. While it’s not absolutely necessary for all materials, a heated bed does a lot for getting the first layer of the print to adhere well to the build platform.
Heated Build Chambers and Enclosures
A heated build chamber is used to prevent warping. It contains the heat generated by the hot end and heat bed, keeping the air warm and reducing drafts. Unlike an enclosure, a heated build chamber includes active heating. This means a heating element and some kind of temperature sensor (a thermistor, for example) are placed inside of the enclosure to heat it up, almost like an electric oven. This can get the air inside very hot and can almost completely eliminate warping with materials like ABS.
Unfortunately, not all 3D printers include heated build chambers. The main reason is that Stratasys owns the patent for heated build chambers, meaning they use them extensively on their professional FFF 3D printers but other manufacturers can’t add them to their printers. If it weren’t for that patent, you’d surely see heated build chambers on a lot of consumer 3D printers.
HOT TIP
Stratasys now owns MakerBot, a popular consumer 3D printer manufacturer. Because Stratasys has the patent for heated build chambers, it’s likely that in the future the technology could be used on consumer 3D printers made by MakerBot. If a heated build chamber is important to you, it might be worth waiting for this to happen.
But that patent doesn’t keep manufacturers from adding an unheated enclosure to their printers. Many consumer 3D printers have enclosures that can hold in the heat generated by the hot end and heat bed, keeping the air warm and reducing drafts. Warm air around the printer keeps the part warm, so even without active heating, this can do a lot to reduce the warping that is common when printing with ABS.
Surface Treatments
Another way to reduce warping is to make sure the first layer of the print sticks very well to the build platform. Most of the materials that build platforms are commonly made from don’t work very well on their own. Even with a heated bed, the filament doesn’t always adhere well. So to make sure that plastic really sticks, a variety of surface treatments can be applied to the build platform. These treatments are usually some sort of tape, film, or glue.
The 3D printing community has come up with a lot of novel ways to ensure the filament adheres well to the build platform. A handful of these methods stand out as being especially effective, and have come to be a sort of standard operating procedure for hobbyists doing 3D printing. There are too many to cover all of them, but I’ll go over some of the more popular ones here.
Painter’s Tape
One of the most popular surface treatments is painter’s tape. This is just the plain old blue tape you put around your trim when you paint your walls. The tape is applied with the adhesive on the build platform, so the entire build platform is completely covered. You then print directly onto the nonadhesive side of the painter’s tape.
Printing a part on a build platform covered with painter’s tape.
The texture of the tape gives the filament good purchase so it sticks well. Some particular brands seem to work better than others, but most of the commonly available types found at hardware stores work pretty well.
Painter’s tape seems to work best for PLA on unheated beds. It can be used with ABS and on heated beds, but there are usually better options. It’s also not a particularly durable surface treatment, so you’ll probably need to replace the tape often (maybe even after every print).
White Glue
Polyvinyl acetate (PVA)-based white glue (commonly referred to by the trade name Elmer’s Glue) is also a popular way to get good adherence to the build platform. This is the same glue you probably used throughout your childhood for various craft projects, and it’s easy to find at just about any office supply store.
To apply it to the bed, mix a small amount with water at a ratio of about 1:1. Next, use a small brush or paper towel to spread it around on the build platform; it can be applied on top of blue painter’s tape or directly to the build platform. Ideally, you want a thin layer left behind as the water evaporates, leaving a sticky residue. The water doesn’t have to be completely evaporated for you to start printing, but the build platform shouldn’t be wet.
This glue helps the filament stick for obvious reasons—it’s glue, after all! When used in conjunction with blue painter’s tape, it can almost completely eliminate warping when printing PLA. However, ABS warps so much that you might not be able to completely overcome it. Also, be aware that you’ll almost certainly need to replace the tape (if using) and reapply the glue before every print.
Polyimide Film
Polyimide film is used in a handful of particular industries and applications, including for superconductors and spacecraft. It’s very strong (even in thin sheets) and flexible and can provide electrical insulation and thermal insulation. Polyimide sheets and tape are usually referred to by the trade name Kapton (developed by DuPont).
Polyimide film, like blue painter’s tape, has a surface texture to which filament adheres very well. Additionally, it can withstand very high temperatures, and there is virtually no risk of damaging it with the heat generated by 3D printers. ABS also sticks very well to polyimide film, which makes it especially useful when combined with a heated bed.
A 12×12-inch sheet of polyimide film.
One of the most desirable properties of polyimide film, however, is its strength. It can be reused many times without damage, which is convenient of course. The only real downsides to polyimide film are its availability and cost. It’s not usually available in local stores and has to be ordered online. And, even when ordered online, it can be fairly expensive.
PET Film
Polyethylene terephthalate (PET) film is used similarly to polyimide film, although its physical properties and traditional applications are quite different. PET film comes in sheets and tape like polyimide film and can be applied in the same way.
In fact, in the context of 3D printing, PET film is really very similar to polyimide film. However, it doesn’t have the same ability to withstand high temperatures that polyimide film has. Polyimide film is often used to hold thermistors onto the hot end, for example, and this is an application PET film isn’t well suited to. It just can’t hold up to the heat from the hot end. But it works just fine for the build platform.
ABS Juice
Probably the most effective way to eliminate ABS warping is to use a sort of glue made from ABS and acetone, commonly called ABS juice or ABS glue in the 3D printing community. Because ABS dissolves in acetone, ABS juice is made by dissolving a large amount of ABS filament (new or from failed prints) in pure acetone, which can easily be found at your local hardware store.
DEFINITION
Acetone is a common household and industrial solvent. Acetone breaks down styrene, which allows it to dissolve ABS.
When kept in a sealed container to keep the acetone from evaporating, this produces a viscous fluid. It can then be applied to the build platform, either directly onto glass or onto polyimide film or PET. This mixture is extremely sticky, and when a thin layer is applied, the acetone quickly evaporates away. After the acetone is evaporated, a film of ABS is left firmly stuck to the build platform.
Once you start printing, the molten ABS filament is deposited on top of this ABS film that is stuck to the build platform. ABS adheres well to itself, and so it sticks extremely well to the film (which remains stuck to the build platform). The result is a print that remains very firmly attached to the build platform.
Using ABS juice can almost completely stop ABS parts from warping, making it very useful. However, it can also be pretty messy to work with. It has to be made ahead of time, kept in a sealed acetone-safe container, and has to be applied to the build platform. And it works so well that it can be difficult to remove parts without damaging them.
Furthermore, the color of the ABS juice will coat the bottom of the printed part. So, for example, if you printed a white part with black ABS juice, the bottom would end up at least partially black. However, this can be counteracted by using a natural (uncolored) ABS filament when making the juice.
Hairspray
One surprising surface treatment that has recently gained popularity is hairspray. The same stuff that gave Farrah Fawcett’s hair its famous flip can help your parts stick to the build platform. And, maybe even more surprisingly, it actually works very well!
As odd as it may sound, hairspray may just be perfect for 3D printing. It’s cheap, it can be found in any grocery store or drug store, it’s easy to apply, it works well, and it doesn’t damage or add color to your parts. What more could you want?
The kinds of hairspray that work best are the ones that are marked with words like extra or super, or ideally extra super hold—the stronger the hairspray, the better. All you have to do is spray a few coats onto the build platform, wait for it to dry, and then start printing! However, it may help to remove the build platform from the 3D printer, if possible, in order to avoid getting hairspray on any of the moving parts or mechanisms.
Hairspray is essentially just an aerosol adhesive, so you’re really just spraying a layer of glue onto your build platform. This works very well to keep printed parts stuck well to the platform, and when used on a heated bed, it can completely eliminate warping. Even large ABS parts can be successfully printed, which is pretty good for a beauty product.
Hairspray being applied the print bed to help the part stick.
The Least You Need to Know
· Build platforms can be made from a variety of materials, as long as they’re very flat.
· Heated beds aren’t necessary for all materials but are required for some. However, they can improve print quality for virtually all materials.
· Heated build chambers can do a lot to reduce warping, but the technology is patented. Because of this, most consumer 3D printers do not have heated build chambers; however, many still use enclosures.
· There are many surface treatments that can be applied in order to improve the adhesion of the filament to the print bed, such as painter’s tape, white glue, polyimide film, PET film, ABS juice, and hairspray.