Types of Gears and How They're Made
From residential washing machines to complex wind turbine generators, every piece of machinery has gears.
But not every gear works for every type of machine. For example, the stereotypical spur gear with straight-cut parallel teeth doesn’t bode well for all mechanical designs.
So, what are your options when you need a self-locking gear? And which type of gear is best suited for heavy machinery?
There’s a gear for everything!
Let’s review eight of the most common types of gears. We’ll also discuss how they’re made, from their inception as CAD models and through the hobbing process.
Spur gears are most recognizable as the “Settings” icon for iPhone and Android apps. These cylindrical gears have teeth parallel to their axis, equally spaced along the circle’s circumference, and precisely cut once hobbed. This novice gear design transfers mechanical energy along parallel gear shafts to control torque and reduce speed in mechanical machinery.
Spur gears are hit-or-miss when it comes to applications. Their single-tooth meshing (one tooth per gear making contact), involute (rounded) teeth, and budget-ready production costs thrive in machines requiring precision and minimal axial loads. But this buttery smooth meshing is also noticeably noisier and likely to undergo stress in high-speed tools.
Spur Gear Examples
Here are a few household examples of spur gears:
- Kitchen blenders
- Electric screwdrivers
- Bicycle gears
- Washing machines and dryers
Helical gears are the second most common cylindrical gears (right behind spurs), but you might mistake one for the other if you overlook the fine details. Unlike those simplistic parallel-spurs, the teeth on helical gears are slanted at 15-46 degrees for firmly interlocked meshing.
Because multiple teeth hook together at once at opposing slanted angles, helical gears step in where spur gears lose their steam.
These gears can support beefier loads and ramp up machine speed considerably without sacrificing a smooth, quiet operation. But the multi-teeth meshing and helix pattern undercuts efficiency and requires a strategically placed bearing to eliminate axial thrust.
Helical Gear Examples
Here are a few examples of helical gears in action:
- Automotive transmissions (as a spur gear replacement)
- Oil-pump shafts
- Cutters and conveyors
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Bevel gears use two intersecting shafts positioned perpendicular to one another (one lies horizontal, the other stands vertical).
While helical and spur gears coordinate their solo axial rotations to transfer energy as a unit, interconnected bevel gears work separately with two axes.
Bevel gears are remarkably versatile (straight, spiral, hypoid), quiet, and the driving force behind modern hand drills. But their dismal torque support, limited speed capabilities, and high production costs make this moderately rare gear more lackluster than anything.
Bevel Gear Examples
Here are some examples of machinery infusing bevel gears:
- Hand drills
- Mechanical garage doors
- Helicopter engines
The bizarrely shaped worm gear looks utterly confusing from a layman’s perspective, but it also plays a pivotal role in low-horsepower electric motors. Worm gears have two main parts:
- The worm (a V-shaped spiral threaded screw)
- The gear (also known as the “worm wheel”)
What makes worm gears unique is that neither the worm nor gear intersects at a 90-degree angle like bevel gears. Instead, they transfer rotational movement.
While these gears run quietly and can handle high shock loads in small-scale machinery, their unique “sliding” motion slices efficiency nearly in half.
Worm Gear Examples
Here are worm gear examples you might be unaware of:
- Banjo and mandolin tuning mechanisms
- Pressing machines
Rack and Pinion
Rack-and-pinion gears are generally regarded as a tried-and-true “rotational to linear motion” strategy.
As the name suggests, there are two toothed parts to the classic rack-and-pinion gear set:
- The rack (the long, non-circular rod with equally distant teeth)
- The pinion (the spur-like gear that rolls smoothly along the rod)
When the stationary pinion rotates, the rack follows its lead, just like a train’s wheels grip onto the track gears to nudge it ahead while ascending a hill.
Rack and Pinion Examples
Here are the most common rack and pinion examples:
- SUV and small truck steering systems
- Railways (for uphill trains)
- Actuator valve controls
Double Helical Gear
Double helical gears are like a helical gear two-fer. Instead of a solo slanted-tooth gear interlocking with its mirror opposite, this cog will position two opposite gears side by side (teeth patterned like a tractor tire) with a narrow gap in between.
Such a simple addition injects extraordinary benefits for thoughtful engineers. On top of canceling the thrust load issue and strengthening the gear’s tooth profile meshing, this gear can also handle higher transmission machinery, like cranes, with little trouble.
Double Helical Gear Examples
Here are double helical gear examples highlighting their broad application range:
- Gas turbines
- Internal combustion engines
Novice engineers confuse double helical and herringbone gears quite regularly, but there’s one distinguishing trait to look for:
Herringbone gears boast V-shaped teeth, just like their double helical counterparts. However, there’s no additional space between these side-by-side cogs.
Their multi-teeth meshing and gapless design allow for stiffer axes, smoother power transfers, and shock or vibration reduction. Unfortunately, herringbone gears are rarely practical unless installed in heavy machinery (like steel mill roller shafts), as slicing the teeth requires specialized cutting machines.
Herringbone Gear Examples
Here are a few herringbone gear examples:
- Torque gearboxes
- Coal cutters
- Steam turbines
- Steel mill roller shafts
Hypoid gears are easy to mistake for bevel gears because of their modest cone shape and seemingly intersecting gears. If you look closely, you’ll see that these spiral-cut gears aren’t perpendicular like bevels.
The smaller gear (pinion) resembles a drill bit, while the larger appears like an unslanted bevel gear. Because of this limited interference and larger contact ratio, hypoid gears are quieter, more secure, and can handle greater torque.
Hypoid gears look like the eerie middle ground between a worm gear and a bevel gear.
Hypoid Gear Examples
Here are a few hypoid gear examples that float under the radar:
- Rear axles in large trucks
- Differential gears
- Right-angle gear motors
How to Make Gears
The gear-cutting process sounds complex when industry experts toss around lingo like “sprockets,” “broaching,” “involute,” and “CNC.”
But if you’re on the crafty side, you can technically make DIY wood spur gears with nothing more than:
- An 8mm brad point drill
- A ⅜-inch plywood slab
- An awl (to mark teeth)
- A powered bandsaw
- A belt sander
- Wood screws
- Nuts and bolts
A Maserati GranTurismo MC Stradale’s eight-speed gearbox wouldn’t support whiplash-inducing top speeds of 188 mph with flimsy plywood gears stuffed inside. Nor will your future can opener, forklift, or electric drill designs thrive without authentic brass or cast iron gears infused into the final product.
Without further ado, here’s a blow-by-blow of the gear hobbing process:
Designing Gears With CAD Software (SolidWorks)
Once you’ve brushed up on your calculus and determined a gear’s ideal dimensions, you’re ready to turn those scrawled numbers and rough sketches into a 3D CAD model.
Here’s a walkthrough of how to make gears in SolidWorks:
- Create a New Part file from the SolidWorks’ welcome dialog box.
- Open the CommandManager and click on the circle-shaped icon.
- Toggle the Smart Dimension tool to input the gear’s exact radius.
- From the Features toolbar, click Insert, Boss/Base, then Extrude to turn this 2D drawing into a 3D gear model.
- From the Sketch toolbar, go to Tools, Sketch Entities, then Centerline.
- Draw a vertical centerline through the gear by dragging your cursor through it.
- From the Sketch toolbar, use the Line tool to draw a gear tooth.
- Turn this tooth 3D by using the Extrude Boss tool again (the same one you used in step #4).
- From the Features toolbar, select Circular Pattern.
- Toggle the Cylindrical/Conical Face option, and then click the outer circumference of your cog.
- Draw a circle on your preferred axis driven through the center of the gear, and then use the Extrude Cut feature once more.
Testing Gears in SolidWorks
Next, want to make sure your two custom gears transfer mechanical energy as they should and can withstand the job without damage.
So, how do you do that?
By experimenting with SolidWorks’ material options!
SolidWorks’ material-rich metal library gives you full creative liberty to design gears that match your imagined design. But before you impulsively toggle the steel option and shun silicon or plastic entirely, think about:
- The total project budget: Silver might be a luxurious choice, but its lofty $200/pound cost will also drive per-gear prices well above budget.
- Heat resistance: If this gear belongs in an engine with maximum temperatures exceeding 200 degrees, a more heat-resistant material like steel is a better choice.
Above all else, consider practicality before settling on a gear material. Research similar models and look for commonalities. If aluminum alloy or titanium appears to be the norm, that’s not a coincidence!
Run it Through a Stress Test Simulation
A plastic manual clock gear won’t survive as a high-torque gear train in a diesel engine, but that doesn’t mean your aluminum alloy gear is a viable alternative. Run a stress test simulation on these cogs in SolidWorks to check for structural and functional flaws that could pose problems later.
Does the gear ...
- Chip its teeth around 1000 RPM?
- Suffer potentially dangerous vibrations?
- Become misaligned after three minutes of continuous use?
- Overheat or melt when performing its duty?
If something seems amiss and your Deformed Result report returns questionable results, return to the drawing board before moving forward. Irresponsibly overlooking something — no matter how minor — could lead to a costly product recall or even user injuries.
The Machine Gear Hobbing Process
After you’ve perfected your spur gear design, including its specific teeth dimensions and a logical material, it’s time to get the heavy machinery involved.
Luckily, gear production is more efficient than ever, with shorter cycle times and more precise machining tools.
Here’s what happens next:
Creating a Gear Blank
A gear blank (workpiece) is a gear’s infant stages — pre-cut, teeth, finish, grinding, and carbon-infusion. First, a heavy-duty bandsaw slices a metal cylinder into perfectly thick, circular gear blanks.
We’ll be referencing steel gears from this point forward, but brass, aluminum, and iron might also be options for your custom-designed gear.
Carbide Tools Enter the Picture
When attached to a turret, carbide-tipped tooling offers high-speed, flawless engraving, thanks to their razor-sharp blades and hardy cutting edge. Factory workers attach the gear blank to a mount to hold it still as a computer-controlled hobbing machine blade makes those initial circular cuts.
The machine will occasionally douse the gear blank with water to prevent overheating or melting.
These nifty carbide tools then take turns fulfilling their unique duties, like drilling the interior hole and carving a shallow inner groove to reduce gear weight and future engine strain.
The Milling Machine
A computer-controlled milling machine applies the finishing touches on the gear’s inner design. It’ll carefully drill evenly spaced holes around the center hole to prevent lubrication from building up.
Adding the Teeth
It’s time to make that plain steel workpiece look more like a functional gear. The cutting machine uses its rough-and-tumble titanium-coated blade to shave away mini interior teeth before the gear hob begins chipping away at the outside involute teeth.
While the hobbing machine can technically cut these outer divots in one swipe, there’s a glaring mechanical pitfall:
Chipping or breakage.
That’s why this device widdles the outer teeth repeatedly until they’re the perfect depth and pitch.
Strengthening the Gear
After the hobber and cutter finish the gear’s outer structural design, the gear goes through a few quality assurance measures.
Depending on your gear’s material and size, it’ll spend some time in a scorching furnace, go through carbon injection, and end with an oil soak. If the furnace, carbon, or oil distorted the gear’s geometric shape, re-hobbing (or skiving) the gear with a cutting tool will return it to its proper form.
The gear is now ready for assembly or installation!
Learning about the different gear types can open the door to new mechanical engineering projects and cutting-edge machine tools.
But hobbing expertise extends much further than being able to distinguish a herringbone gear from a helical gear.
It begins with brushing up on your mathematical skills to master functional gear manufacturing and design. That means knowing how to calculate:
- Gear ratios
- Circular pitches
- Reference pitches
- Pressure angles
If those all sound like a foreign language to you, take an online calculus intro class. That’s the best way to revive your derivative, geometric, and power calculation expertise while you’re honing your SolidWorks and mechanical engineering skills.
Check out RocketGear’s course catalog for more of our interactive online mechanical engineering classes!