Intro: Gear Set for 3D Printing
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)
Step 1: Gear Design Basics
To use the gears presented here you only need to concern yourself with a few things:
- Center Distance - How far apart the centers of two gears should be in order to mesh properly
- Outside Diameter - Outer diameter of the gear, needed for clearance
- Pitch Diameter - How far away the gear needs to be from mating gears' Pitch Diameters
Step 2: Auto-Generated Vector Gears
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
- If you don't already have Inkscape, you can download the free vector software from their website, inkscape.org
- Open the program and create a new document. You can just use the defualts if you like.
- On the upper menu, click EXTENSIONS>RENDER>GEAR...
- The gear option box will pop up. Set the number of teeth you want, set the circuilar pitch to 5.3 pixels, and set the pressure angle to 20 degrees. These settings determine the distance between teeth (Circuilar Pitch) and the sharpness of the gear's teeth (Pressure Angle). I've choosen the given values to great the smallest teeth I could print while still being functional.
- Click Apply
- Save the file as an inkscape.svg file
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.
- Open the Inkscape file with illustrator
- Cut a center hole from the gear by using the circle tool to create a circle at the center of the gear (turn smart guides on to snap to the center.) Use the object properties to set the radius of the circle to .25mm.
- Select both the gear and the new circle, and click the "Pathfinder" Subtract button. This will cut the circle path out of the gear path.
Step 3: Making Stylized Vector Gear Spokes
Cutting Out the Center of a Gear
- Draw a circle at the center of the gear, taking its edge 1 mm away from the teeth of the gear. In the above example this is the green circle.
- Draw another circle ontop of the green. Make this one 3 mm wide. This is the pink circle.
- Subtract the pink circle from the green circle by selecting them both and click on the Pathfinder Subtract option .
- Select your newly formed green doughnut and the gear behind it, subtract the former from the latter. This will cut a doughnut shape out of the gear and leave behind the center axle hole.
- Copy and paste the vector of your choice over the gear. Again, center the object and use shift+alt to scale it up. You want the edges of the object to extend past the inside of the gear so that it can later be cut to a perfect fit. If there are fine lines in the design they likely wont print. I find that a minimum thickness of 1mm works very well with the Up!3D.
- Double click on the gear to enter "Isolation Mode", where are the cool kids are. Here you can select just the inside circle of the gear's inner doughnut. Press ctrl+C to copy that circle.
- Press escape to exit Isolation Mode
- Press ctrl+F to paste the circle in place. This will paste a new circle in the exact position you copied the original from. In the pictures this new circle is red in color.
- You want the red circle to be under your vector art. If needed you can press ctrl+[ or ctrl+] to move it's position in the level hierarchy.
- Select the red circle and the vector art, click the Pathfinder Intersect tool. This will cut the overhang off of the vector art.
- To get the objects to combine correctly the vector art needs to overlap the gear just slightly, select it and scale it up just a smidgebit.
- Select the vector art and the gear, click the Pathfinder Combine option to merge them into one. You now have a path that can be imported cleanly into other programs.
- Save the art as an Illustrator file.
Step 4: Making a Vector Into a 3D Editable Solid.
Getting an Illustrator Vector into Inventor Fusion
- Start up SolidWorks and open the Illustrator file created in the previous step.
- Click the Extrude button
- Set the Extrude depth to 1mm
- Save the gear as a Part files (prt.)
- Open the Part file with Inventor Fusion and save it as a DWG file
- During the import the center hole may end up not registering as a circle, making it difficult to snap to it's center. If this is happening to you, draw a slightly larger circle around the center hole and extrude the difference.
- Save the file again.
Step 5: Making Spokes
Creating Spokes Inside a Gear
- Open the gear in Inventor Fusion.
- Click the "Create New Sketch" button and select the face of the gear as the new sketch plane.
- Draw a circle that is 1mm larger than the desired center hole.
- Draw a 90 degree vertical line from the center of the gear to the outer edge.
- Draw another line from the center at a 120 degree angle from the first line.
- And yet another line from center, this one 120 degrees from the last.
- Use the Offset tool to create lines at least .5mm from the lines made in the last three steps.
- Draw a circle that is 1mm away from the teeth of the gear.
- Select the three, large inner sections and cut them through the gear.
Step 6: Making Compound Gears
- Open the gears that you want to compounderize.
- Copy one gear and paste it into the other gear's file.
- Using the "Assembly" tool, select the inner circle of the second gear and snap it to the center of the first.
- Select both gear solids and Boolean them into one solid.
- Add spokes and save for printing.
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
Arranging Gear Dummies
- Draw two circles to represent the gears you want to match, use the outside diameter (OD) to set the size. The distance between these two circles will be the Center Distance as provide on the chart. Here I've drawn a circle for a 8 tooth gear (5.9mm OD) and a 48 tooth (29.8mm OD) that are 16.85mm apart from each other.
- Extrude both of the circles as separate, new components.
- Repeat the circle drawing beginning at the center of the last gear. I'm adding another 8 to 48 tooth set so the dimensions are the same as the last.
- Extrude the new circles, adding the smaller gear to the larger gear made in step 2. Make the new 48 tooth into a new component.
- Add as many gear sets as you need.
- Arrange the gears so that the overlap, add .1mm clearance between the sides of the gears and other parts.
- After creating the gear box frame go back and use previous steps to make the compound gears that you will need.
- Draw a line connecting the centers of all of the gears, except the one that will be connected to the motor.
- Draw a 3mm diameter circle around each of the gear centers.
- Draw a tangent to tangent line between these 3mm circles (click and hold the first circle, drag over final circle.)
- Trim excess construction lines.
- Extrude the frame part as a new component.
- Copy the frame component and paste it to the assembly as a new component.
- Use the assembly tool to attach the new frame part to the other side of the gears.
- Start new sketches on the inside of the frames, draw 3mm circles around the centers and extrude them to the faces of their gear.
- Add .1mm clearance between the gears and the frame.
- Create a new sketch on one of the frame pieces to extend the frame to where the motor will be.
- Draw a circle to the same diameter as the motor you intend to use. The motors used here are 7mm in diameter.
- Offset the circle and extrude the cylinder roughly 5mm.
- Press/pull the inner side of this cylinder (the side facing the gears) in a few millimeters to give room for the gear and the end of the motor.
- Draw a rectangle on the side of the cylinder and extrude it out 4mm. This piece will add much needed strength to the cylinder-to-frame connection.
- Chamfer the corner of the rectangle to transform it into a triangle.
Gear and Gear Box Design Guidelines
- Gears should be a minimum of 1mm thick, any thinner and they get floppy.
- To allow room for the gears to turn freely, there needs to be at least .1mm clearance between each gear and the box frame.
- The size of the center holes in the gear and the pivot holes in the box frame will vary depending on the size of the shafts you intent do use. It is best to print these holes smaller than the shaft so that they can later be drilled out by hand. For example, for 1/16" diameter rods I make the holes 1mm in diameter and use a drill bit to cut away the access.
- The gear box frame support structure should be at least 2mm x 3mm thick.
Step 9: Making Gear Boxes Prt 3 - Printing, Fine Tuning, Assembly
- Print your gears and box frame.
- Cut brass rod into sections that are long enough to go from one side of the box to the other.
- Drill out the center of the gears and the holes in the frame. Try to make these holes at a perfect 90 degree angle to the gears and frame if you can, but don't sweat it if you are a little off.
- To make a gear spin freely around the brass rod, use the drill bit like a file and ream out the center of the gear until it spins. Same goes for holes in the frame that must allow the rod to rotate.
- Assembly the gear box and try spinning them around. Here will be able tell what parts need filling down, which you can while the box is assembled.
- Keep filing until everything runs smoothly, make sure that the box isn't too tight.
- Take the gear box apart and use a dremel tool to size and polish the ends of the brass rods.
- Use the file to roughen the sections of the rod that will be glued to printed parts.
- Super glue the brass rods to the frame and gears where needed. Don't glue the gears to one another or the frame! Be really super careful not to get glue any where you don't want it, there is no going back after this point!\
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!