Bearing
Spline Shaft Mounting
Splines are an excellent way to transmit torque and centre a gear for high power applications. They are used in automatic transmissions, in couplings between engines and gearboxes, and
Involute Splines
Parallel Key Splines
Ball Splines
| Involute Spline Profile | Parallel Key Spline Profile | Ball Spline Profile and Function |
|---|---|---|
Keyed Shaft Mounting
Friction Fit Mounting
Tapered Shaft Mounting
Interference Fit Mounting
An interference fit is the simplest way of fixing a gear onto a shaft. It requires no extra components, but may require a press or hammer to assemble and disassemble. It also requires that the shaft and bore of the gear be precisely machined so that the tolerances of the interference fit are met. For most cases,
Set Screw Mounting
For light loads and fast assembly, a set screw can be used to lock the gear onto the shaft. In most cases, the shaft is required to have a flat or divot where the set screw makes contact. This avoids raising a burr on the shaft, which would make the gear nearly impossible to remove. Brass or nylon tipped set screws can also be used to avoid marring the shaft if it is not possible to add a flat for the set screw. It's important to note that even if the shaft has a flat, the diameter of the set screw and tip geometry has a large effect on the allowable torque. If the set screw is small, the tip will see very high contact forces as the shaft tries to rotate relative to the gear, so it should be made as large as possible.
The amount of torque able to be transmitted by this mounting solution is highly variable - it depends on the surface condition of the gear bore, whether the assembly was lubricated prior to assembly, and how much torque the user applied to the set screw as they tightened it. If the set screw is not held in place with a second set screw or permanently secured with a threadlocking compound like Loctite, it can loosen over time, allowing the gear to run spin, which would destroy the gear and the shaft.
In most cases, a gear secured with a set screw will not be as well-centred as a gear secured with a friction fit or spline shaft. In most low speed and low torque applications that set screws are used for, this is fine, but if there is a large amount of clearance between the shaft and gear bore, the gears will not mesh smoothly because the effective centre distance will change constantly, leading to wear and noise.
A pulley secured to a shaft using a set screw. Note the mark on the shaft flat.