What it is
A set of small, matching gears intended for 3D ABS extrusion printing, along with instructions on how to make your gears and gear boxes. After printed gears for my own projects I eventually wound up with this set, that I'm calling "Gear Set 1", and created a reference chart to aid in the pairing of its gears. Gears from this set, printed from ABS on an up!3D printer, have been tested thoughtfully, but I'd wager that they would also work well for laser cutting.
Back in the day I had a some Lego Technics that came with a set of plastic gears that I absolutely loved to fiddle with. I spent hours building little contraptions only to tear them apart and build something else. Eventually I left the legos behind and moved on to building things from scratch materials, but I never really had a way to make gears myself and ended up just buying motors with gears already attached.
Fourteen-years later 3D printing becomes something that you can do at home, and with it came the ability to just print out my own gears. Remembering my Lego set, I headed out with the goal of creating my own version that could be mixed and matched for whatever thingamajig I was was working on. It took a lot of software hopping and a lot of test printing, but eventually I was able to make a set of gears tuned for the up!3D.
I've included all of the gear files that I've made in this Instructable along with reference chart you'll need to use them. The gears are made to the absolute smallest size that I was able to print f while still getting something that actually works.
The rest of this Instructable will explain how to generate vector gears, make them into 3D solids, and ultimately, design gear boxes around them. I must warn you, this method is more convoluted than ideal as it uses a total of four programs to get from vector to dwg, but the end result is worth it in my opinion. It's worth noting that Autodesk Inventor (not Inventor Fusion) can generate 3D gears all by itself. I would have just used that but, well, it had lots of options that I didn't understand.
You can get the DWG and STL files in the ZIP below, or you can download them from thingerverse (www.thingiverse.com/thing:49614)
Gear Set 1 - Specs.pdf80 KB
Gear Set 1.zip17 MB
Gearset 1 - Vector stencil.ai260 KB
Step 1: Gear Design Basics
It turns out that designing gears can be very complicated as there are dozens of variables that, when perfectly calculated, allow gears to mesh together smoothly with very little friction. Although I like to pretend, I am not a professional engineer and the finer points of gear design are lost on me. For the purpose of these instructions we are not going to worry about all of the variables, as they would likely just hinder the creative process. Cutting these corners will result in a less than optimal gear, but you know, whatever, they work.
To use the gears presented here you only need to concern yourself with a few things:
Gear Set 1 - Specs.pdf80 KB
Step 2: Auto-Generated Vector Gears
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To create the vector outlines for the gears we are going to let software do the thinking for us. I know of two ways to automatically generate vector gear outlines: with inscape (which is what will be used in this Instructable), and the gear template generator at woodgears.ca. To use woodgear.ca templates you'll need to save the page as a pdf, then it can be opened in Illustrator.
For the most part, I picked this tecnique up from this Make blog that explains a bit more about gear specs.
Creating Gears with Inkscape
Editing the Inkscape.svg with Adobe Illustrator
Later on we'll be using Solidworks to import the vector and it is necessary to save it as an illustrator file.
Step 3: Making Stylized Vector Gear Spokes
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Sure you can make nice simple spokes for your gear with some rectangles, but as long as we are using vector illustration software we might as well embelish. In this example I'm using a lady bug vector that I got from all-silhouettes.com and am combining its path with the path of a gear.
Cutting Out the Center of a Gear
Step 4: Making a vector into a 3D editable solid.
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Now that we have an illustrator file with the vector image at a 1:1 scale we can make it into a 3D solid with SolidWorks. Once saved, the gear can finally be opened in Inventor Fusion.
Getting an Illustrator Vector into Inventor Fusion
Step 5: Making Spokes
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To save on weight and material I like to remove as much of the inside of the gear as possible. After testing I found that a three spokes worked well as long as the spokes are at least 1 mm wide and 1mm thick. It is also helps to fillet the corners where the spokes meet gear, thus strengthening the connection.
Creating Spokes Inside a Gear
Step 6: Making Compound Gears
Compound gears are two or more gears that are stuck together at their center. The process is fairly simple now that the gears are made, it's just a matter of aligning then merging them.
Step 7: Making Gear Boxes prt 1 - Planning
Typically, motors spin very, very fast but don't have much torque. To slow a motor down enough to, say, drive a robot around, a combination of gears is used to turn speed into turning power. All that is needed some basic math to figure out exactly what combinations of which gears we should use. The gear box show here is simple compared to the complexity possible, but it should get the idea across.
While creating gearboxes in Inventor Fusion I do not use the actual gear models, they are too complex and my poor computer starts to lurch. Instead I represent the gears with disks that match the outside diameter of the gear I intend to use. I then open the actual, toothed gears separately for compounding and printing.
In case I didn't mention it before, gears are complicated, so here I will be describing only the most simple of gear boxes. Once you understand the concept search for "gear ratio calculator" and you're bound to find dozens of webpages that will do that math for you.
I have a pager motor that turns at 18,000 RPM and I want it to be slower. I would start with an eight-tooth (yellow) gear connected to the motor and use it to drive a 48 tooth gear (orange.)
8/48 = 1/6
The eight-tooth gear needs to make 6 complete turns to turn the 48 gear once.
1/6 * 18,000 = 3,000
For every 18,000 turns of the eight-tooth the 48 tooth will turn 3,000 times.
3k RPM is still to fast and so more gears are needed. This is done by attaching an eight tooth to the orange 48 tooth gear to create a compound gear that then drives yet another 48 tooth gear (blue.)
1/6 * 3000 = 500 RPM
Still too fast. Ok, add one more 48 tooth (light orange.)
1/6 * 500 = 83 RPM
At this point the total reduction is 1/216 (1/6 * 1/6 *1/6.) More often this ratio is written as 216:1; the motor must turn 216 times to turn the final gear once. This is a slow enough speed with enough torque to drive a small robot.
So, I all I need to do is use an eight-tooth gear to drive two compound 8/48 tooth gears and a single 48 tooth... I'm hoping that the picture fills in the gaps left by my description.
Step 8: Making Gear Boxes prt 2 - Gear Box Frame
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To put two or more gears together you need to know how far away their centers are from each other, that's where the reference chart comes in. By using the dimensions provide there you can determine the center distance for any two pairs of gears in the set. Again, using disks to represent the gears will help save computer resources.
Arranging Gear Dummies
Gear and Gear Box Design Guidelines
Step 9: Making Gear Boxes prt 3 - Printing, Fine Tuning, Assembly
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No matter what type of printer you use to make these, the gears will likely need some light sanding to operate smoothly. This is escpecially true for the 8 tooth gear as it rides right on the line of having too fine of detail. Another issue with prints of this size is that, due to the nature of extrusion printing, one side of the gear will be slighting wider than the other side, this drafting can prevent the gears from meshing properly. You will know which parts will need the sanding by building and testing the gear box, then it can be taken apart for quick go over with a hand file or emery board.
Pager Motor Bonus Tip
Fiddle with one of these little motors long enough and the wires will certainly break off. What's worse is that they will break off inside their insulation, making the damage almost impossible to notice. I've wasted chunks of time testing control signals only to realize that the motor is kaput!
After breaking four of these motors within two weeks, I started looping the wire leads a bit down the motor so they could be held in place with heat shrink tubing. So far, this has prevented any damage.
Step 10: Go Forth and Assemble
Personally, I think gears are pretty cool on their own, but I suppose they are really just a means to an end. For gears to truly fulfill their destinies they must use their rotational force to better the world in some way. So far I've used these gears to make a dozen (unsuccessful) flying machines and am working on a robot base that uses photo-interrupters to count the gear spokes as they spin past. Next I plan on scaling the gears up a bit so that they can be attached to stepper motors that drive some kind of arm.
Although I created these gears as a quick resource for my own projects I certainly hope that they be of use to others. You may of course feel free to use, share, and modify any and all files as you please. If you do use them it would be pretty sweet if you posted a picture of your resulting contraption in the comments.
Got any tips on creating and/or printing gears? Well, if so you should leave a comment about that to!