After the material leaves the nozzle, it lands on your build plate. The build plate is a surface on which you build your part layer-by-layer. The component itself is also a part of the mechanical system, but right now, we'll discuss it in terms of extrusion. The build plate is the final step in the extrusion system. The aspect of the build plate that factors into the extrusion system, is a build plane. This is the layer on which extruded material lands. When a print starts, the build plane is the same as the surface of the physical build plate, but as the build progresses, the build plate rises moving up higher and higher, becoming the topmost layer of the pair part. The important thing to discuss when we will talk about the difference between the build plate and the build plane, are material adhesion, cohesion, warping, elephant feet, and heated build plates and surfaces. Along the way, we'll explore a range of popular solutions that can help you have a better experience with your next 3D printed object. When anyone asks me to name the biggest obstacle for newbies in this field, I always start here, with build plate adhesion. For this whole process to succeed, the material needs to stay where you put it. This means that it has a stick or adhere to something. There are many approaches you can take to solve this problem, and we refer to these as adhesion strategies. Before anything else, it is critical to calibrate the build plate. While we have mentioned the build plate from the perspective of the motion mechanical system, I think it's important enough to repeat here now. In order to have a good first layer adhesion and accurate parts, you need to make sure that the build plane is properly calibrated so that where your nozzle is driven across the XY plane by the motion mechanical subsystem, it remains the same vertical distance from the build plane, everywhere. One way to remind yourself how this works, is to focus on the pair of terms I mentioned earlier. Build plane, ie, the plane established by the territory of everywhere the nozzle could potentially reach, a plane that will begin to rise as more layers of the part are constructed. Also build plate, ie, the top surface of the plate itself, where you deposit the first layers of the part. When a print starts, these two flat planes should be precisely parallel to each other, with just the first layer of plastic keeping them apart. When you successfully bring these two planes into alignment, the machine makes an accurate model of where the platform and tool head are located, and a precise part without warp and skew is possible. You often hear people say bed leveling, but that term is confusing. You don't care if the machine itself is level to the world. You only care about the relationship of that nozzle, its range of motion, and its distance from the build plate just below. Another term for the CNC milling and machining world that is a more accurate metaphor, is tramming. When a CNC mill trams the top surface of a work piece, it is cutting away the material across the plane to guarantee that the value understood by the CNC about the work plane is perfectly reflected in the physical world, as well as the digital world. Sorting out this element first is actually more valuable than most of the other adhesion strategies because when the build plate is improperly calibrated, the chances rise considerably, that you're part will fail, it will fall off or be deformed or otherwise defeat your adhesion strategy. There are adhesion strategies that occur before your print begins, things that you'll add to your design file and Cura or Slic3r. These include: rafts, skirts, brims and mouse ears. They're also physical measures you can take during the actual print job. These adhesion strategies are applied to the surface of the build plate and include: glue, tapes, and films, and the use of a heated bed. You can also purchase this issue by thinking about cohesion or bonding, as opposed to adhesion. Cohesion describes materials sticking to materials, through chemical or mechanical processes. Let's go back and talk about the adhesion strategies you can implement in your design. The most aggressive solution is called a raft. In your design, you'll account for one or more layers of material set down flat on the plate, and you'll then use this as the base for the rest of your part. It ends up looking like a platform you might see beneath a sculpture. Think of a sculpture of a horse. You only have the hooves of the horse touching down on the base. If it doesn't stick well, then the entire horse will be lost. But by having a place to anchor those skinnier, flimsier parts, the sculpture works. The material from your print will stick to itself more easily than other materials. So by using a raft, you're likely ensuring a nice, sturdy object fixed down. If a raft acts like a pedestal for your print, a brim looks more like a single layer extending out from the base of your object in all directions, like the brim of a hat. While it serves a similar function to a raft, providing a larger base for sitting the printed part, it's also solving the additional problem of cooling and warping. As the edge of the part is exposed to the air and cools, more rapidly than the rest of the part, it shrinks slightly moving away from the print. By using a brim, you've delayed the cooling and warping of the important parts of your object. Some operators will model a raft into their designs, but you can typically use your 3D control software to automatically generate a raft. That's the most common. When you produce a raft in this fashion, the way the layers are printed will be unique to each raft, guaranteeing that it sticks to the plate and can also be pulled away from the base of the object. This is performed through a combination of adjustments to the height, the flow rate, the speed, the temperature, and by adding a slight gap so that the contact of the base, the part, is different than the layer-to-layer bonding throughout the rest of the print. After you've finished printing the part, you should be able to easily tear away the brim. A skirt is produced the same way as a brim, but the layers are offset away from the base of the object and do not come into contact with the final printed part. While this doesn't necessarily seem like it would help with adhesion, by printing the skirt first, you're priming the flow rate of your extruder. Thereby, ensuring that the first material is flowing well enough, that the part itself will adhere completely. Without the skirt, the first layers might not adhere as reliably. A skirt can also help visually guarantee that the build plate has been properly calibrated to the nozzle. If the skirt is not an even height, getting thinner and thicker in different places, then you should stop the print and re-calibrate your build plate. It's like a test drive that you take around the block, if the block is the build plate. Mouse ears were an early strategy in 3D printing, similar to a brim. A series of flat disks were incorporated into the design around the base of the model. After the part was printed, you could easily tear the discs away from the finished product. While less frequently used than other solutions, having this option available when designing can be helpful, especially if you encounter just a single tricky edge that you need to fix. We'll now move onto the physical measures you can take during the actual print job to ensure proper adhesion. Lets start with the heated beds. These were a late arrival in desktop 3D printing, but had been used in industrial 3D printing for years. When using a heated bed, you have a heated surface that is not hot enough to melt the printed part, but it's warm enough to keep the base material a bit pliable and prevent it from cooling and pulling away from the plate. Common materials for heated bill plates include aluminum and borosilicate glass. Borosilicate glass is the industrial material that Pyrex baking products used to be made of. For a heated build plate strategy to work, you need to have a heating element in your 3D printer and a temperature monitoring solution to maintain the perfect Goldilocks temperature for your part. One of the potential setbacks from heating the plate too aggressively, is called an elephant's foot. An elephant foot error is when the temperature is high enough, that the lowest layer of the print has melted and expanded around the object. It looks a lot like an elephant's foot, wide at the base and tapering off at the edges. Not all machines have a heated bed, and it's possible to have a good adhesion by providing a better base of material that stick down regardless of temperature. The simplest way is to give your prints something to grip. The earliest build plates were made of materials as diverse as pine and phone core. If you look at these surfaces under a microscope, even know they're flat to the touch, you'll notice micro fishers deep enough to give the melted plastic plenty of opportunities for adhesion, like little footholds on the side of a mountain. The glass plates used today have actually been sandblasted or chemically etched to offer more points of purchase. If your surface doesn't offer quite enough grip on its own, then you can apply adhesives. The most popular solution has many different faces. I'm talking about PVA glue. My favorite version that you can use is the PVA extrudable material itself, using multi-material printers to act as a sacrificial support structure, later dissolving away in water after print is finished. Would you believe that an Elmer's glue stick is made of a similar PVA substance? Some people prefer to spray adhesives down on the plate instead of rolling it on with a glue stick or printing down PVA material. A popular solution is to use hairspray, low-cost hairspray like Aqua Net, etc, is mostly just glue. It behaves like an Elmer's glue stick, except it may include various perfumes and relaxers. You need very little PVA glue to hold the part down because PVA tends to stick pretty well to most build surfaces, and most printing materials. When you use this in combination with a heated bed, PVA glue offers another advantage. It helps evenly transmit the heat to the base of the part, and a twisting or levering action causes it to lose its grip, making it easier to remove your part at the end of printing. Substances like tough PLA grip down onto the build services so aggressively, that if you don't use glue as a release agent, your part might be stuck there on the build platform forever. There are other glues in use, either specifically created for the field of 3D printing or for other industrial applications. For a long time, the most popular solution for printing PLA onto a cold surface, was to use 3M Blue painter's tape. The value of this tape to the printing process is a lucky happenstance, and observers of this trend have sometimes mistakenly used the wrong brand of tape thinking it to be equivalent. The reason that 3M Blue painter's tape works so well is two fold. The adhesive can be removed without leaving a residue, that's part of their patent, and the top surface of the tape has particularly good micro fishers, making it an ideal grippy material for hot plastic. Those who have tried other brands of Blue paper tape, have found that what they use didn't have the adhesive power or the special top surface to help with their prints. There are other specialty tapes available that offer similar properties. In addition to tape, there are adhesive films that can be held or adhered down to the build surface. Examples include PEI and Catch On tape, films that are both used in other aerospace and industrial contexts for coating and heat transmission. These are particularly effective on heated plates. In addition to tapes that stick onto your platform, third party adhesion systems, like the BuildTac FlexPlate and Easy Stick from GeckoTec offer excellent part adhesion and easy part removal. As the markets evolve, you will likely see more and more third party products available to help you solve this sticky challenge.
