If you're new to the world of designing objects to be 3D printed or if you just want to learn a few design tricks for SketchUp or some other program read on. If not... read on anyway, it couldn't hurt. What qualifies me to teach you this? Nothing. I'm probably no different than you. I'm a jack of all and master of none. I built what was probably one of the world's most sensitive barometers just for fun. When I go to sleep I spin 3D objects in my mind's eye. I bred worms and crickets. I weld, I drive huge machines and dodge death every day at work. I also designed and built my own 3D printer over a year ago. And I eliminated about five hundred parts from my 3D printer design. It's bill of materials is currently about 110 parts all together. I do a lot of weird stuff and 3D printing helps me do it. I've also designed a few ways to destroy the planet... I'm really just a lair and a few minions away from doing some serious damage.
3D printing demands sacrifice. Mostly time and money... Sometimes sanity. Like any hobby what you get out of it depends on what you're willing to put into it. Short on time? Throw money at the problem. Short on money? Dedication and effort can usually fill in the gaps in your wallet. Short on time and money? Download a free STL and take your chances. The internet is full of dirty geometry that will make your logic cringe and scurry screaming under a rock. But with some time and effort you don't have to rely on someone else to design what you want. You can do it YOURSELF!
The Software Chain
Once you've become bored of the world of free STL octopi you'll want to create something. That means you need to design something then export it as an STL. After that you need to slice it and export it as G-Code. Then your printer can totally disappoint you by not being built properly and nothing sticking to the bed. I'm going to stick with CAD design and making the STL files, everything else is your damn problem.
Choosing CAD Software
Spoiler alert! I picked SketchUp. I tried some other software, Tinkercad was too simple and depended on an internet connection to function. It also tended to crash when forced to think about anything more complex than a chess set. Blender... lost a lot of time on that one. Read a couple books, watched a bunch of tutorials, even put little shortcut stickers all over a keyboard. In the end the universe of solid objects defined by nurbs was a wash for me. Powerful and free but too clunky and the learning curve was a constant uphill battle. Autodesk was about the same as Blender but also came with a crippling price-tag if I wanted to sell my designs. I am currently learning Fusion 360 which is a free to use Autodesk product but I don't feel I'm at a level where I can write about it. FreeCAD didn't appeal to my visual, hands on nature. Using FreeCAD is like writing music. You can do it and you can write a song but it's more fun to pick up a guitar and just start playing with it to get instant results. SketchUp came in a free version that is almost as fully featured as it's paid version. The free version lacked the Boolean operations (that I don't really use anyway) and the licensed version was only a few hundred dollars instead of a few thousand. What's a Boolean operation? It's where you overlap two (sometimes more) objects and either join them or use one as a cutter to remove part of the second object. Like addition and subtraction but with stuff instead of numbers.
Sketchup is a SURFACE modeler! It will let you do ANYTHING including screw up! I suggest changing the default greyish blue / bluish grey color scheme to red and light blue. Then you can tell at a glance if any parts of your model are inside out (yes this is a thing). Most people build something then try to slice it and print it and it turns out to be molten garbage and mid air nozzle dancing. You have been warned. If this strikes fear into your heart go get Fusion 360.
Most tutorials won't go into this at all, something I find incredibly surprising. There are no tone deaf musicians... well, probably no good ones and certainly none of those are writing good songs. However, lots of folks without a creative bone in their body own or want a 3D printer. You CAN get by just downloading stuff made by random designers on the internet. If you're willing to spend a few bucks you can even pay to get some really nice files made by some very talented people. But chances are pretty good that you will never find exactly what you want unless you design it yourself. You don't have to be a creative person to design 3D objects but it sure helps. You do however have to be able to identify a need for a design. This can be one of three types of design. Being able to recognize what kind of design you're after will help you to focus and be creative.
The Three Types Of Design
Simply put there are three types of design. First order, second order and third order. First order designs are direct replacements. You break out the digital calipers and copy a broken part... simple child's play. Lost the battery cover for a toy so you make one. Second order design is a bit more difficult. You don't just make a replacement, you make it better by making it stronger and/or simpler. Sometimes you redesign it so it can perform a dual purpose like moulding in a point to help you remove the old batteries. Third order design is when you design a whole new and unique toy or object. Third order designs are rare. It's the seed of an idea. The seed is the problem or function you want to make a design to address. It usually starts as something you're just tossing around in the back of your mind for a few days. Then it sneaks up on you and comes out of nowhere. Being a third order designer is not easy. To be honest sometimes you just hit a wall and even though you have the seed of an idea the execution of it can still elude you. I usually break out the big paper, a new box of crayons and a bunch of booze when I hit that wall. Sometimes it works but most of the time I just end up passing out and getting a crayon stuck to my forehead. Keep a pen and paper with you at all times. Moleskine note books come in all sorts of sizes and will stand up to all kinds of abuse. Buy several and use them (do NOT leave them in pockets when you wash clothes!). Leave a pen and paper in the bathroom, leave one beside the bed. Hang a dry erase marker off your bedroom mirror. You never know when an idea will hit you. Write down the idea and make a little drawing. Make sure you can read it then go back to sleep. You can figure it out in the morning. Long boring drives and drifting off to sleep seem to trigger ideas in me... your experiences may vary.
Printer Design Limitations
There are limits to what you can physically print on a 3D printer. Your print bed will probably be 200 millimetres square. You won't be able to print anything much taller either. Even if you have a larger printer most other printers are that size so if you want to share your design keep that in mind. Your first reaction will most likely be to find a large format printer. Don't bother if you're just starting out. Most things I make are the size of a beer can or less. Unless your only reason for getting a printer is to make full size Storm Trooper armour you can wear to Comicon it's very likely you won't need a large format printer. Remember, if you double the size of something you increase it's volume by EIGHT! A five hour print could become a FOURTY hour print! A lot of things can go wrong in fourty hours! Overhangs and unsupported parts of your designs are something to consider too. If you couldn't build it out of wet sand on the beach it's probably going to be difficult to print without support. Consider how something may delaminate. Since 3D prints are made of layers of fused plastic they are going to fail by those layers separating. Orient your designs so the layers are as long as possible or have a lot of surface area. For example. If you print a chopstick standing on end you would end up with many small circular layers... very easy to snap. If you printed it laying on it's side the layers are all very long with a great amount of surface area... much stronger! As a general rule anything that comes off the bed at 45 degrees or more will print pretty good. If you can't design your parts so they can print in the strongest way possible while laying flat on the bed you may need to use support material.
Good Mechanical Design
Complication is bad, the more parts something has the more things that can go wrong. If you can eliminate one part and make another part do two jobs do it. If it can do three or four jobs that's even better! If you can eliminate a screw or a bolt without compromising on the strength of the item do it. Never use two different types of fasteners or sizes of bolt when you can use one. If someone has to source five different sizes of nut and bolt to make your design they will hate your guts. Use commonly available inexpensive sizes of hardware, bearings and fasteners. Skate bearings for example (8mm ID, 22mm OD) are available everywhere for very cheap at very high quality and can take a lot of abuse. Buy these in bulk if you intend to use bearings in your designs. Don't mix metric and imperial if you can help it but if it will cost less do what you gotta do. Personally I use metric bearings and smooth rods with imperial fasteners because of the high cost of metric stuff around here. Look at how it is put together. If there is an adjustable part can it be accessed? Can you get a wrench or screw driver in to adjust it or assemble it? Trap nuts when you can. Design in washers and spacers. Taper holes so screw heads lay flush. Fillet corners and radius edges. A sharp corner or edge is a weak point. A nice radius on an inside corner will distribute forces across the rest of the structure. Even if the part doesn't need the strength it just looks better. Keep removing bits from your design until removing just one more piece will make it unable to function. Don't worry about beauty. Dan Gelbart said “Airplanes are all beautiful because there is no room there for additional weight.” “If you want it to be beautiful just design it to be 100 percent functional. If you remove all the material that is not needed it will become beautiful all by itself.”
Your Design Space
Everybody is different. Maybe you have a laptop, maybe you have a computer tower. Use whatever you're comfortable with. But you must use a mouse and keyboard at the same time if you're serious about getting anything done. And you need a mouse with a scroll wheel on it. Personally I use a Logitech M570 trackball mouse and an acer i5 Laptop with 8 gigs of RAM. I like the trackball mouse because it lets me “fly” through the SketchUp 3D environment very quickly and I don't have to move my arm either. Not having to move your arm doesn't sound like a big deal but think about that next time you're on a plane or a bus and you have a few hours to kill. A flick of my thumb and I can be on the other side of my model in an instant. The Logitech SetPoint software also lets you map the extra buttons on the M570 to handy things like “Hide”, “Unhide” or “Line Tool” and “Eraser”, I think I had “Undo” and “Erase” mapped at one point but now I use “Hide” and “Unhide” So I can quickly peek inside my models. When I'm really serious I hook my laptop to a 55 inch LG TV using an HDMI cable and I hook up a Logitech wireless keyboard too. The Logitech Unifying software ties everything together quite nicely. Then I can work from the couch with my feet up... so that's nice. Aside from that the only other things I use to design are digital calipers, a pen and some paper.
Shooting The Puppy
Don't get too attached to your designs. If something is an obvious improvement be brutal about it. Just because you spent ten hours making that part doesn't mean you need to use it. Cut it apart, use the faces as templates for the new improved design and move on. Perhaps keep a copy of the old design on file but stop going in dead directions.
SketchUp will quickly populate your entire desktop in .skp (SketchUp) and .skb (backup) files if you let it. Make a folder in your documents. Call it SketchUp. Inside that have files named after your various projects. When you make something take the time to NAME IT PROPERLY! If it's an evolving design use version numbers like 1.0 1.1 1.2 don't ever leave a file called “Untitled”. That way madness lies. Use a backup system regularly. Laptops tend to get dropped. I email stuff to myself and let Google store it on it's servers for me. It's like the cloud but it's free and I have millions of dollars worth of servers and backup servers saving my work on Google's equipment. By the way, you can change a .skb backup file to a .skp SketchUp file by simply renaming it if you want to use it.
Well I suppose we will just carry on. In future musings I'll go over extensions, the tools SketchUp has, sizing holes so you can use metal hardware, resources, drawing with accuracy, making things manifold and well... lots of stuff really. But we will (mostly) move away from the concepts and core ideas of designing into actually using the tools SketchUp has to offer. I will be explaining some core differences between SketchUp and some other CAD software as we run into them. Honestly, I'm just pulling this out of my ass as I go.. I got no firm plan. Stay tuned for more.