I get this question a lot. What the heck do you do with a 3D printer? I usually answer it, in a somewhat cryptic way, as "What don't I do with my 3D printer?"
I had the same question when I first bought one 3 years ago, but figured I'd find some use for such a novel device. Turns out, it's much like a computer. When the IBM PC was first introduced in 1984, people thought they'd use it for recipes. That was actually one of the only things they could think of. Seriously. Well, after 32 years of personal computers, we've changed our mindset, and now, we immediately think of the computer as a solution to most every problem. Things we never imagined in 1984 - booking a flight, finding a movie, driving directions, typing a letter, planning a project, on and on. And, now smartphones have blown that wide open - the plethora of apps let us do things we never dreamed of.
This is how my mindset changed about 3D printing. Here's an example. You know how something will break in your house, or you'll need a small doo-dad to attach this thingy to that thingy? You used to go to hardware stores and spend hours looking for just the right thing to do this. Maybe the part is obsolete and you have to kluge some other thing to do the same job.
Not any more. Just make it on the printer. It took a while for my mindset to change, but now, that's the first thing I think of doing.
But, how do you make an obscure part like that? Well, there's a couple of ways and I'll get to those in a second. But first, you need to know that scanning the part isn't a solution. People usually immediately suggest that to me. When you scan a part with a 3D scanner, 2 things are missing. First you don't get scale information - ie. the actual, exact size and detailed dimensions of the object - at least not very accurately. And, second, you don't get interior details, like insides of screw holes, cavities, etc. It's a lot like taking some pictures of a house and asking a builder to build you one like it. There's no interior details and no dimension information.
But, back to how can you make a part? 2 ways. A real great way is just to search the internet for it. There's some great places like thingiverse.com, grabcad.com, or pinshape.com - just google "3D printer objects" or go to this site all3dp.com/best-sites-free-stl-files-3d-printing which lists 34 free sites for stuff to print. You'll find literally thousands of predesigned files for everything from iPhone holders to drone parts to bottle openers to hot tub chemical floats. It's all been done and lots of the parts are very well designed by experts.
Secondly, you can design your own part. Along the lines of using PowerPoint to draw a picture, but a bit harder because you're working in 3D. I use Alibre Geomagic Design - a professional grade 3D mechanical design program that allows you to combine parts into assemblies and animate their interaction before you print them. Saves a lot of wasted printing. It's a great piece of software, but unfortunately I can't recommend them as their customer service policies are not very favourable. Too bad, it is good software.
Here's a couple of simple custom designed parts to solve a problem - first one's a vacuum hose attachment for a chop saw and the second is a little screw in bung that we lost for a paddle board. Both would have required hours and hours at the hardware to figure out how to replace.
Free software abounds for this. Google Sketchup and Tinkercad are great, although I find Design much easier.
Once you've designed an object, you need a slicer engine to take that object and send it to the printer. No problem, some printers come with one, it's kind of like the printer driver you use for your paper printers. You can also get free ones - like Cura. I use Simplify3D - about $149, but well worth the investment - very versatile, great for when you really advance in the art of 3D printing.
Next.....another question I get - "What kind of 3D printer should I get?"