Prints of Darkness

Because of the way that FDM (fused deposition modeling) 3D printing works, with clever design techniques, we can print functional assemblies in one job. Most FDM printers can print fairly large overhangs without using any support material. In fact, from a recent test, I found that the MakerBot Replicator 2 can print up to about a 30o angle from the horizontal without the use of supports. Because of this, it is very simple to make a hinge, if you know the tolerances of your 3D printer.

Let’s say you have a pair of sunglasses that you want to print as one part. (click here for the thingiverse file) There are 5 different interacting features that we will use to define the parts of the glasses; the frames, the two lenses, and the two sides. Obviously, we want these glasses to fold so that they can be compact, which involves the creation of a hinge, but that will complicate the assembly process. So let’s see how we can take advantage of 3D printing to simplify the number of parts in our design. As mentioned earlier, a hinge is very easy to make on a 3D printer, as in its simplest form it only involves two parts; an axis, and something to rotate around said axis. Keeping the tolerances of our printer in mind, and remembering the fact that FDM printers can print decent overhangs, I have designed a simple hinge for a pair of printed sunglasses involving two cones, our “axis”, and two extrusions with cone-shaped recessions.

The cross section of a hinge on a printable pair of sunglasses.
The cross section of a hinge on a printable pair of sunglasses.

To make sure that none of the parts fuse together during the print, we need to leave some gap between the side piece and the lens piece. On the printer I’ve been using, a .02 inch gap did the trick, giving the hinge enough clearance to print safely, while keeping it tight enough to prevent the side piece from falling off entirely. This value varies from printer to printer, so you may need to do some testing of your own to determine your printer’s tolerances (it took me about 3 or 4 prints to get it)!

The next step is the lenses. I’ve introduced co-processing in my previous blog post, and here is a situation in which it can be applied. As the printer was printing the cavity for the lenses, I was able to pop them in and continue the print!

Placing lenses into sunglasses during a print
Placing lenses into sunglasses during a print

While not applicable in this example, if the piece you are placing into your co-processed part is flat, the printer can print on top of it as long as the printed has been dimensioned correctly, with proper tolerances. For example, if instead of placing in real sunglasses lenses, I had cut out pieces of flat glass to put in the cavities, the printed can fairly easily print over the glass to seal off the rims. This process will be demonstrated more in later posts.

While this process will get you a nice pair of sunglasses, I tried to test out one more co-processing technique. On FDM printers especially, parts tend to be weaker on the XY plane (parallel to the build plate) because each layer creates another seam that the part could snap on. I was afraid that the side pieces on my sunglasses would snap easily, so I added a small hole running through the center of each of the sides. I then took some 1/16th inch steel rod and fed it through the hole once the print was tall enough. Although I haven’t tested this on any materials science loading machines yet, I believe that this actually strengthened the sides of the glasses because the steel rod serves as a stronger and less brittle core to the sunglasses.

Placing steel rod into the sides of the sunglasses to make them stronger
Placing steel rod into the sides of the sunglasses to make them stronger

In this example, I’ve shown through design and co-processing how to use 3D printing to your advantage to create interacting materials and parts in your print jobs. Because of the way we’ve designed these sunglasses, they are both a simple design and not easily breakable for 3D printed parts. While in an assembly, especially when it comes to repair, the ability to take apart a product comes in handy, co-processing allows us to strengthen and improve the parts that are important, even when we cannot disassemble the work. Better still, with good design techniques, one will still be able to disassemble the product after it has been co-processed.

A fully 3D printed pair of sunglasses, printed all in one job.
A fully 3D printed pair of sunglasses, printed all in one job.

Thanks for reading!

Alex Crease


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