How to Get Real-World Shapes (especially weird ones) Into the Computer for 3D Printing
Many 3D printers end up used mostly to create knick-knacks, though we justified buying the machine with all the useful stuff we could make! One of the reasons for this is that Baby Yoda’s dimensions aren’t exactly critical to it’s purpose, but the broken knob you wanted to replace has a weirdly shaped fitting that won’t work unless it’s just right, and how do you measure that? Then how do you design something to fit it?
There are a few methods! What follows is my low-cost, low-math method for replicating weird shapes for 3D printing.
You’ll need: the part you want to work with, paper large enough to cover it, a pencil, a ruler (the finer the measurement, the better), your 3D design software of choice, and your slicer.
For my example, I needed to make porthole trim rings with a lip. My boat had 10 portlights with beautiful cast bronze trim rings on the hull, but on the stern it had four strangely shaped holes cut roughly, exposing the edge of the plywood.
I taped paper over the portholes, and traced the outline from the inside. If you’re working with a small piece or can’t get inside the thing for whatever reason, take a rubbing by rubbing the side of a pencil lead or a crayon on the paper where the edges of the object are. The edges should come out clearly enough to take measurements from. Then, draw a grid on your tracing or rubbing.
The more curved your piece is, the more reference lines you’ll want in your grid. This piece had a nice right angle with two flat sides to reference, but if yours doesn’t, just extend the lowest and leftmost parts of your piece so they meet at a right angle, and build your grid from there.
This is how I gather measurements to input into a 3D design program- how you input them will depend somewhat on your program of choice, and I’ll save an in-depth description of that for a later post. Here’s how the rest of this project went, though.
I created a rectangle in Blender, then used the slice tool to create vertices at each of my measured distances from the y axis (Fusion 360 is more optimized for dimensional design, but Blender can do it and is open source). In Blender, you can make a slice and then input the exact measurement for its placement. Then I did the same from the x axis. That placed vertices at the measured points along the curve of my object. Deleting faces from the rectangle and joining vertices into new faces “carved” the basic shape from my rectangle, and then I mostly used the extrude tool to get my final shape.
Turn on mirroring to save yourself time if it applies to you, but also pay attention to when to turn it off! For me, I created the object, but turned off mirroring to emboss the words I wanted into the design. Your slicer can be a good tool for checking whether your design is “manifold.” Usually it’ll highlight the areas that aren’t, and show an error. Sometimes you can print even if it isn’t manifold, but it’s best practice to fix it, because it can affect printing in unpredictable ways.
I printed a prototype in cheap, recycled PTEG.
Then in bronze filled filament from Protopasta!
https://www.proto-pasta.com/collections/all/products/bronze-metal-composite-htpla?variant=7154346098733
This filament has so much bronze in it that it will patina like bronze, and can even be polished. It isn’t cheap, but this was much more doable for me than casting from real bronze, and having all four portlight rings custom cast would have been over a thousand dollars.
