Join Kacie Hultgren for an in-depth discussion in this video Planning the project, part of 3D Printing a Scale Model with AutoCAD.
- In this video, we'll plan out our project. By looking at our 2D drawings and considering the print volume of our printer, we'll decide the size and scale of our model. Our starting file is essentially a simplified version of an orthographic projection of a small house. In the middle we have a plan, then a front elevation, a side view, and a section. We have everything we need to create a 3D model. Now, before we start, let's get a sense of scale.
I find doing so really helps me avoid over-modeling, for example, spending too much time creating details that will be too small to see. It also means that I can optimize my model for 3D printing as I go, making smart decisions that will create a model that will print reliably. Now, with a project like this, you usually have two options. Maybe you have a scale that you were required to work in, or you might be able to adjust the scale to fit the project.
In this case, we'll do the latter. Now, we have a lot of scale factors to choose from. See this list of common scales. For this project, I'm going to work with an imperial scale, and I'm guessing that a scale somewhere around a quarter-inch to the foot will work well. Now, if you're working in metric, scale factors are a lot easier to deal with, but with imperial, we need to do some extra math. We'll convert a quarter-inch to the foot to a scale factor that we can use.
A quarter-inch to the foot is our scale factor. Let's break it down. A quarter-inch is .25 inches, and a foot is 12 inches. .25 inches times our scale factor equals 12 inches, and if we solve for the scale factor, 12 divided by .25 is 48. Now, let's do the same math for some similar scales, and you get 96, 64, 48, and 32. Now we have our scale factors. Let's go back to AutoCAD to see which will work best.
Let's visualize the proportion of the build platform. I'm going to use a MakerBot Replicator 2. In CAD I'll create a rectangle that is 6.2 by 11 inches, that represents the size of the platform. But I'll make four copies, scaling by our scale factors of 96, 64, 48, and 32. I'll lay the rectangles on top of our plan to visualize. Two of these are too small, and another, too big.
My favorite is 3/16 to a foot, or a scale factor of 64. Now, I like this scale, because there's enough space to fit the model in one print, and leave some extra room to include some of the site plan, added text, and a logo. My Replicator 2 can accommodate a model that's six inches tall, that's a little bit smaller than the short axis of the platform, and just by eyeballing it I can see that there's plenty of room in the Z direction at this scale.
Now, we'll use the scale factor in two ways. To go from model scale to full scale, multiply by 64. To go from full scale to model scale, we'll multiply by one over 64, which is .0156. Now, I want to do some math so I can answer the question, how thick will the walls, windows, details be in scale? I'll use an equation. The dimension times the scale factor, times the conversion to metric, will give us the dimension in scale in millimeters.
Now, the walls of our house are six inches thick, which means that in model scale they'll be 2.4 millimeters. That's printable, but what about one-inch-thick details? How big will they be? .4 millimeters is pretty small, and that's okay for surface details, but for the most part, one inches thick is gonna be too small to be printable. How about two and three inches? Three is printable, but I want you to take careful note of two inches.
In scale, that will be .8 millimeters thick. Each thread that my printer prints is .4 millimeters wide, so .8 millimeters is two threads thick, and that's the smallest dimension I should use for printable details. Now, it's worth noting that these are my tried-and-true values for Replicator 2. If you're using a different brand of printer, you might need to develop your own rules for "printability." The key is that you wanna have an idea of what is printable so that you can save time modeling and have confidence that the model you're creating will print well.
Armed with this information, we're ready to start our modeling project.
- Working in scale
- Extruding solids
- Working with blocks
- Creating terrain with lofting
- Adding 3D text and logos
- Converting mesh files to solids
- Breaking a model into pieces
- Exporting and optimizing for 3D printing