In the introduction to our gears series we wrote about Backlash and Gear Ratios. Now that you have more background information on gears we can break down the five gear types and some advantages and disadvantages. Let’s start with the most commonly used gear: the Spur Gear.
The advantages of using spur gears in your application may be obvious. Efficiency and ease of assembly are going to save you time and keep downtime to a minimum, but what about the disadvantages? For example, the noise at high speeds is due to backlash and the instantaneous force the teeth of the gears experience when they first engage. The force can lead to wear and tear over time, which can decrease the efficiency of the gears.
A possible solution to this problem is plastic spur gears which are useful in lightweight applications and applications where noise must be kept at a minimum. Similar to the plastic spur gear, a bonded plastic spur gear with a carbon steel core and MC Nylon teeth helps keep noise levels down as well.
Another thing to consider is that spur gears can only engage properly if they are used in parallel, due to their straight tooth profile and location of the bore. In the example below, two spur gears are being used to slide a work piece from the right to the left.
The Bearing Built-In gear type allows you to synchronize the direction of rotation between two opposing gears as shown in the picture. Another special type of gear is the keyless spur gear. The keyless spur gear is available in three different types: E Type, F Type & G Type.
- E Type: Keyless spur gear has a similar shape to the A type gear but has a bushing fastened to the outside of the gear.
- F Type: Has the same shape as the A Type gear, but with a bushing attached to the inside of the gear’s width.
- G Type: Keyless spur gear is similar to our B Type gear, but has a bushing attached to the outside of the gear.
Helical gears have a diagonal tooth profile which allows them to be quieter and smoother then spur gears, since the teeth engage more gradually. Helical gears have the ability to be mounted in Parallel or Crossed. When the gears are crossed, you must select Same Handed Gears, Both Right, or Both Left. Some of the disadvantages of helical gears are they are less efficient then spur gears due to tooth slippage. The diagonal profile of the teeth is what causes the slippage and also leads to axial thrust on the shaft. It is important to choose a bearing that can withstand the axial thrust generated by the gears.
Bevel gears are used for intersecting shafts and have a changeable operating angle due to their shape. Some of the disadvantages of bevel a gear is they are difficult to assemble due to the changeable operating angle. The shafts also experience a large force, so like helical gears, it is important to ensure the bearing can withstand the force. Depending on the manufacturer, Bevel Gears can be found in two types; Straight Type and Spiral Type.
- Straight Type: Similar to spur gears and prone to suffering from backlash and excessive noise.
- Spiral Type: Similar to helical gears due to their similar tooth orientations, quieter than the spiral but prone to tooth slippage.
*It is important to note that spiral bevel gears are only guaranteed to mesh with a gear from the same manufacturer and they should always be bought in pairs.
Another type of gear is the Rack Gear and can be found in two different styles; the Flat Type and the Round Type. The advantages of rack gears are when paired with a spur gear or pinion; they can transfer rotary motion into linear motion. A disadvantage is they cannot run continuously, since the rack will eventually end.
A nice feature of flat rack gears is the number of mounting hole orientations. Depending on how you plan on mounting them you can either use side tapped holes, bottom tapped holes or side counterbored holes.
Worm gears are composed of two pieces, the Worm Wheel and the Worm Gear. Worm gears are self-locking and quiet, but suffer from high power loss and high thrust load on the Worm.
Regardless of your design requirements, remember that there are a variety of gears available, each having unique benefits. Additionally, there are solutions for linear motion as well as rotary motion. Hopefully, this break down of gear types has you thinking about new application designs or how to solve problems in existing ones. In the meantime, keep an eye out for part 3 of this series!
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