The first time I saw a 3D printer make a working mechanical object, it was impossible for me to comprehend how it could possibly have been made. The expensive 3D printer I had been watching spit out a perfect little crescent wrench, complete with fully functioning adjusting screw and sliding jaw... No assembly required.
How 3D printers are able to print objects with moving parts is difficult to imagine, but very simple to explain. Working mechanical objects that contain adjusting screws, sliding jaws and hinges are made of individual interconnected parts. At the points where these parts come together, a tiny space exists between them. And just like your inkjet printer is able to leave tiny spaces between areas of ink, the 3D printer can leave tiny spaces between areas of plastic.
The clamp in this instructable is made from 2 parts connected by a hinge and an adjustable snapping leg. I made it to temporarily hold bundles of wires together when I get around to rewiring my sports car. After printing it, I realized it can can be employed to do many other things as well, from clamping ski poles together, controlling wires under a desk or acting as napkin holders for a steampunk dinner party. I'm sure everyone can come up with dozens of good ideas.
And that's what makes this a great candidate for a fun and educational project.
Expensive machines that use dissolving plastic, liquid baths or powder to support overhanging walls are able to print incredibly precise and detailed mechanical things. With careful planning, home printers are also able to print working mechanical things, but maybe with a little less detail and less precision (not all that less... The hinge in the middle of the 1/4" square bar sitting on a quarter was also printed on my machine)
Because most home printers use the same material to both print and support overhangs, adding support material inside the spaces intended to allow mechanical movement will only result in a fused brick with no hope of ever working. By eliminating all support and making the tolerances between parts relatively large, the initial plastic that overhangs the gap will sag, but the time it takes the printer to lay additional layers around the gap allows the layer's lower surface to cool, preventing the upper portion's plastic from fusing completely. The parts will stick together, but the bond is imperfect and can be easily broken afterwards. The loose material in the gap serves to decrease the tolerances and the parts will move the way they were intended.
Step 1: What You'll Need
For this project, you'll need a 3D printer. Today, these can be had for less than the cost of an iPhone and if you have school aged children, owning a 3D printer has become imperative. By the time they graduate, today's elementary school kids will be entering jobs that don't yet exist, using tools that have yet to be invented. Introducing them to new technologies at a young age is a very wise thing to do
You won't have to get involved with 3D design for this project, but if you get the printer, you'll eventually want a way to print things out of your own imagination.
The only CAD program I use anymore is Sketchup Pro. Like other open source 3D computer programs, Sketchup is free to download and use. The difference is, Sketchup is the easiest, most intuitive 3D CAD program available and with free plugins, the free version can do everything the pro version does. Trimble Navigation calls Sketchup, "3D for the rest of us". Within a few hours, you'll be creating 3D printable objects no one but you has ever seen before... And that, my friends, is an indescribable feeling everyone should experience.
Step 2: Concept
Eliminating the need for support between moving parts is helped by adding lots of room inside the hinge for the printed material to sag. The distance between parts also increases the time the lower layer has to cool before the layer above it is added.
This clamp is designed to be printed at a .02mm resolution. Each layer, once put down by the printer is .2mm high. As the photo shows, the wide horizontal gaps in my example are filled with fuzzy bits of loose plastic that have sagged and solidified inside the space. Once hardened, this drooping plastic acts as support for the rest of the layers above the gap. And when the part is removed from the printer, it will be as rigid as any printed object, but the weak connection between the strands in the gaps are easily broken the first time the part is used and it will work and perform as designed from that point on.
For this print, I've made the horizontal gaps .75mm (.030") and the vertical gaps .5mm (.020"). I've also reduced the points where the two halves come closest together as much as possible. This reduces the surface area of the plastic that can possibly touch and melt together. The .75mm gap can also be reduced to .500mm, but the force required to break the parts free may be increased and there'd be no working advantage. I want this first example to snap easily and show the concept without tears.
The final 2 images show what the individually parts would look like if printed separately. It's easy to see how it would be impossible to assemble these parts by hand and demonstrates how useful a tool a 3D printer can be.
One more cool thing can be done with the printer used to make this device. You'll notice 2 pins being printed next to the hinge. These are markers indicating the point where the printer reaches the first and second gaps. I haven't done it for my example, but if desired, the printer can be stopped when these points are reached and .010"-.015" washers can be placed over the center shaft. The washers not only act as support material for the upper overhang, but they reduce the tolerances between the parts and the hinge will perform even better. Markers are a very useful technique for embedding non-plastic materials into your prints and something I'll describe in more detail in upcoming instructables. The downside of adding things to your print is, the printer must be carefully watched. But if you're new to the process, that's something you'll be doing anyway. For now, take a look at another ongoing project that uses this technique.
Set the part to be printed with no raft or support, 30% fill and one shell layer (adding additional shells causes the sides causes the part to swell and the likelihood of the parts melting together increases.
The smaller the resolution, the smaller the theoretical gap needs to be. Myself, I'm too impatient to print often at less than .2mm. If you do use higher resolutions, just be aware that the ribbon of plastic the extruder lays down is wider than it is tall, so making narrower gaps for smaller resolutions won't necessarily work to keep the hinge's parts from fusing together.
Step 3: Experiment
Once you've seen and understand how 3D printed mechanical parts are made, you'll be ready to begin working on your own hinged, geared and sliding devices. One of the very first hinged objects I printed was a gag set of chopsticks I made for a friend's restaurant. The sticks are dumb, but the questions the diners kept asking about how they could possibly have been made kept me smiling for days. As I stated up front, the technology that can print working objects is difficult to comprehend, making it perfect for getting an audience.
The cable clamp is far more practical than hinged chopsticks, but the possibilities they open up between them are endless. I've included another stl file for a cable clamp that uses a different type of hinge. The new hinge is effective on small items, but in cable clamp size, it's not as strong or stable (wobbles side to side a bit), but I think the clamp itself looks cleaner. It certainly broke apart easy enough. If you print both, you can compare the 2 types of hinges for yourself. Again, print it at 30% fill, one shell layer and no support.
Use your imagination to make things that work right out of the box and get attention when you explain the miracle machine that made them.