What’s the first thing that comes to mind when you think of gears?
- Shifting gears while driving?
- Grinding your gears at a frustrating situation?
- A grain-powered gear train?
Or, since you’re looking for information on gear types, did you think of spur gears?
Spur gears are known for their simplicity in design, efficiency in power transmission, and cost-effective price for multiple applications. But it isn’t the only gear type out there.
In this post, we’ll discuss some of the most common gear types, their applications, and their drawbacks.
Spur Gear
With teeth parallel to the axis of rotation, spur gears are used to transmit power between two parallel shafts. This parallelism ensures no thrust load is experienced in the axial direction.
Spur gears are easy to maintain due to their simple shape, allowing many issues to be diagnosed quicker than their more complex counterparts.
Seen in everyday items from washing machines to watches, they have a wide range of capabilities from high load capacity to precision in timing.
As with all things, nothing is entirely without flaw. At higher speeds, spur gears have the tendency to create noise and vibrations. Having more of a rattling grind than a clink, it can be caused by how the teeth enter and exit meshing. This can be amplified due to a design error such as bad center distance layouts or because of issues in fabrication, such as a poor tooth surface finish.
Gear Rack
Imagine taking a spur gear, making a singular cut from the bore to the outer diameter, opening it flat, and you’ve made a gear rack. Typically described as “a section of spur gear with an infinitely large diameter,” these gears are characterized by their linear shape allowing the rotary motion of a spur gear to be transferred into linear motion.
If you’ve ever driven a car, you’ve used a gear system that includes a gear rack. The steering wheel connects to a pinion, a round gear, which drives the steering gear rack. This system converts the rotary motion of turning the steering wheel into the linear motion of pushing your tires towards the direction you want to go.
Similar to spur gears, gear racks are not meant for high-speed applications and can also create noise with more of a clank than a grind. Although you can connect multiple gear racks in series with specifically manufactured parts, this can take up a significant amount of design area that might not be readily available.
Ring Gear
Now we’re going to take that gear rack and reconnect its ends with the teeth facing inward to create one of the most important parts of a planetary gear system, a ring gear. These gears are to be used in combination with spur gears to create a system that can provide high torque in a compact space.
Commonly found in cordless drills, ring gears help a planetary gear system keep constant meshing with uniform loading to help reduce any unnecessary wear and noise. No clink-clank here. Another advantage to using a planetary gear system is the high reduction ratio, which can be used in applications that need to lower the speed of input rotation.
A disadvantage of using ring gears is the cost to manufacture. Ring gears cost more more than a typical spur gear or gear rack due to the complex geometry of the teeth. Additionally, thrust forces are generated along the axis of rotation and would need to be compensated for with thrust bearings that can handle the load.
Comparing Gear Types
| Feature | Spur Gear | Gear Rack | Ring Gear |
|---|---|---|---|
| Shape | Circular with teeth parallel to the axis of rotation | Flat, linear “unrolled” spur gear | Circular with inward-facing teeth |
| Motion Transfer | Rotational → Rotational | Rotational → Linear | Rotational → Rotational (used in planetary systems) |
| Typical Application | Washing machines, watches, general machinery | Car steering systems | Cordless drills, planetary gear systems |
| Advantages | Simple design Easy to maintain High-load capacity Cost-effective | Converts rotary to linear motion Can be extended in length | High torque in compact space Constant meshing Uniform load sharing |
| Disadvantages | Noisy at high speeds Susceptible to vibration | Noisy (clanking) Takes up space Not suited for high-speed | More expensive to manufacture Generates axial thrust forces |
| Noise Profile | Rattling grind at high speeds | Clank | Reduced noise due to uniform meshing |
| Design Complexity | Low | Moderate (especially when connecting in series) | High |
Take a look at Spur Gear Tooth Geometry: Understanding Gear Module and Pitch Diameter to learn more on the proper selection of gears for your application.
For more information on gears, consider reading Gears Part 1: Backlash and Ratios.
Explore MISUMI’s wide range of gears.
