In my recent status report for Madeup, I shared a picture of an H-shaped box that I designed in Madeup and printed. I actually had to print two, because when I showed my friend Heather, she wanted one too. Maybe you want one? But what if your name doesn’t start with H? Well, I offer here a general recipe for making hollowed boxes of any shape that doesn’t have holes in it. Our example will use the letter “I” because of its simplicity.
The core idea is that we need a function that walks the outline of our box’s guiding shape. For a blocky I, that shape is a plain old rectangle:
Now, we’re going to need to draw this shape several times at different locations and with different dimensions. We drop it into a function:
Now we draw the shape four times:
For steps 3 and 4, we inset to the inner wall by moving our starting location in by the thickness of our wall, and we shrink the width and height by two wall thickness. The end result is four contours:
Now we use the
surface solidifier, which will connect each vertex to its four neighbors: the two neighbors on its own contour, the corresponding neighbor on the previous contour, and the corresponding neighbor on the next contour. We tell
surface how wide and high our grid of neighbors is and check out the result:
Almost great. The
surface solidifier isn’t smart enough to fill in the floors. We can do that manually by walking the floor contours again and running the
polygon solidifier. Which side of a 3D polygon is intended to face out is not something an algorithm can figure out, so we check the default direction and then
flip as needed:
There we go! We’ve got a watertight model with the floors facing opposite directions.
Making the H is very similar, but the guiding shape has more turns and a few more parameters because of its concavities. The horizontal bridge between the verticals actually gets longer on the inner wall.
A similar process can be used to create a lid. An inset will help secure it in place, but make sure you inset by a bit more than the wall thickness to allow for expansion of your material. 0.5 mm works on my MakerBot Replicator 2X.
If your box is radially symmetric, it’s probably easier to