Supports, Rafts and Drain Holes for better 3D Prints

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Instructor Rick Barrett

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In this tutorial, you’ll learn the value of each of these, and how you might need to keep them in mind while preparing models for 3D printing in Cinema 4D.

Rafts, skirts, brims, supports and drain holes are all solutions to the limitations of the 3D printing process. In this tutorial, you’ll learn the value of each of these, and how you might need to keep them in mind while preparing models for 3D printing in Cinema 4D.



In this tutorial, we'll take a look at some specific limitations of the 3D printing process, the solutions that 3D printers have come up to solve those limitations and how those affect your modeling process in Cinema 4D. We'll start with Rafts, Skirts and Brims because they're probably the simplest and also the first thing that your printer is going to lay down. Rafts, Skirts and Brims are used specifically with extrusion-based printers, the type that spit out plastic and print sort of in an ink jet-like fashion, moving the print bed downward as they extrude the plastic in layers to create your model. A raft is several layers of plastic that the printer lays down first that provides a solid foundation for your model. It helps to counter bed leveling and Z offset issues. It also helps the plastic that's extruded keep adhered to the print bed so that it doesn't curl up and warp and cause issues with your 3D print. For these, we're going to look at a simple cut model and we're going to look at them in Simplify3D because it has options to do all of these methods. And here you see a raft. It's basically this purple that's going down first, and then the green is the beginning of the actual model. Rafts have many advantages, and I end up using them on a lot of my 3D prints. The downsides, of course, are that you're using more material that you're just simply going to throw away, and also a raft is going to take away some of the smoothness of the bottom of your model because it's not being printed directly on the bed. A brim is basically the same thing as a raft, but it doesn't extend under the model. It's basically like the brim of a hat, just extending from the edges of the model outward a little bit. It helps with bed adhesion, but it doesn't provide that foundation that helps to counter any leveling issues with your printer. So if we look at that, I'm going to go ahead and switch on the brim here. And here we can see what that looks like. The brim is the purple here at the bottom, and as I drop down to the lower layers, what you'll see is that we get the green bottom of the model in these very first layers, and the brim is going around the outside of that. So it's going to help to keep the model attached to the print bed, but again, it doesn't help with issues of print bed leveling. Finally, we have skirts. What these are are basically brims that are not attached to the model, but they're a few millimeters away from the outside of the model. And these serve a very different purpose from a brim. They don't help with bed adhesion at all, but they basically just prime the extruder and help to establish a flow of filament. So we'll take a quick look at a brim. We go in here, and again, they're very much the same brims and skirts, so they're in the same options here. And basically to make a skirt, we just set an offset. So we'll set this to a four-millimeter offset and go ahead and print this. And here you can see that we have this purple outline that's completely separated from the part. Now I have exaggerated the size of both the skirt and brim to make them a little bit easier for you to see here. You normally wouldn't print them this wide or this tall. So with rafts, skirts, and brims, there's not a whole lot you need to be concerned with within Cinema 4D in the preparation of your model. The only thing to keep in mind is how your model is oriented, and how the raft or the brim might affect the smoothness or cleanliness of your part once you've removed those pieces. So next, let's take a look at supports and overhangs. Because extrusion-based 3D printers print upward from the bottom of your model to the top, each subsequent layer of the print needs to have material underneath it to support that next layer. So here we have an example of an overhang on the right and a bridge on the left. An overhang being a situation where one side is supported, and a bridge where there's support on both sides but there's an unsupported area in the middle. In both of these cases, the 3D printer is going to want to add support structure to hold the plastic up in these areas where it's unsupported underneath. The amount of support structure necessary depends on your 3D printer and the amount of overhang that it can handle. And the type of support structure that's generated is going to depend on your slicer. This is one of the key differentiators between slicers. If we look at Simplify3D for instance, it has the option to generate the supports based on an overhang angle. So here you can see that it's creating supports entirely underneath this overhang on both sides, but Simplify3D also has the option to add and remove manual supports. Some slicers just create the supports for you automatically without any option to adjust them, and some actually allow you to go in and say, "I don't need support here or here or here because I happen to know my 3D printer's limitations." So generally you want to avoid supports if possible because, again, they use additional material and also they can create a bit of a mess when it comes to actually removing them. So your finished 3D print is not going to be as smooth as you'd like. So when you're preparing your 3D model, you should consider how you can adjust your modeling process to eliminate the need for supports. For instance, in these simple examples, if I just round out these radiuses and make two archways, I'm going to need much less support, if any support at all, because there's more material under each layer to support even as it's bridging across that gap. Now, of course, that may not be your vision for your 3D part. And the other thing that you should consider is orientation of your model. In this case, any other way I orient this model is going to eliminate the need for supports entirely. If I were to take both of these and sit them flat on the print bed, like so, I'm not going to need any support at all because each layer simply builds exactly on top of the layer above it. And if I were to print this upside down, again, I'm not going to need any supports because each layer is completely supported by the layer underneath. So as you're preparing models in Cinema 4D for 3D printing, keep in mind the best orientation for the model, and also try to avoid any pieces that overhang more than 45 degrees from vertical. Now the last thing we want to discuss in this tutorial is drain holes, and this is shifting gears a little bit because drain holes are not an issue at all for extrusion-based 3D printers just like supports are not an issue at all for powder-based printers because the powder is always surrounding the model, and so there's no need for support during the print process. However, with commercial services and high-end printers that use powder, you need to provide a way for that powder to escape from the model. An extrusion-based printer will simply generate one of those hexagonal infills within a model, but a powder-based 3D printer prints a solid piece of material, and so these types of prints are actually priced based on the volume of your object, how much powder is actually used in that object. If you add a drain hole or an escape hole, you allow that material inside to escape so that you're not having to pay for it. So as a simple example here, we have a model that Patrick Goski sculpted, and this is a solid sculpted model. If I go in and simply add an interior shell and drain hole to this model, all of that material inside it is allowed to escape, and the total volume of this model is cut in half, which also basically cuts the production cost in half. Let's take a look at this model in shapeways, and you can see that the original model is going to cost $615 to print in this particular material. However, by adding the drain hole, it gets cut down to $317. Now obviously I'm not going to be printing this model in either form at those prices, but I wanted to illustrate that a drain hole makes a lot of difference in your 3D printing. Now the thickness required in your model's walls as well as the size of the drain hole is going to vary based on your printer and material. So for instance, here on shapeways we can choose each of the different types of material. Let's take a look at gold, for instance, and we can see that we need a minimum thickness of 0.8 millimeters and we need an escape hole that's four millimeters in diameter if we have one escape hole, and two millimeters in diameter if we have two or more escape holes. But again, this is going to vary based on your materials, so you're going to have to refer to your commercial printing service or your printer itself to determine what's necessary. And again, if you're doing extrusion-based 3D printing, you don't need to worry about this at all because it's simply going to honeycomb the inside of the model. So that's a brief overview of rafts, skirts, brims, supports and drain holes, and I hope that it helps you be more successful and save both time and money in preparing your 3D prints.
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