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Shaft Coupling Ideas

Shafts convey torque from one location to another -- like a drive shift, conveying torque to a bell-housing and trans-axle. Since the dawn of the mechanical age, shafts have been integral in machinery of all kinds and the search for new and better designs has continued. Throughout the design history, a handful of ideas have formed shafts into categories.

Splines
- Splines are a commonly used mechanism to couple shafts. A spline end looks like a star-drive type screwdriver tip. The shape of the spline prevents spinning when inserted into an inverse spline coupling, creating a contiguous mechanical bond. Splines essentially function like Phillip's head screw drivers. The spline applies torque through its shaft to another shaft the way a screwdriver shaft transfers torque to a screw.
Universal Joints
- A universal joint, or u-joint, is a specific design for coupling shafts. It consists of two "U" or horseshoe-shaped couplings that connect to another in an interlocking arrangement. The use of u-joints allows a shaft to continue spinning while changing directions. U-joints are often used for allowing small directional changes in the shafts. They're typically not used for straight couplings or several bends in the shafts. A shaft that must veer off 10 degrees, for example, might use a universal joint, but a shaft that must redirect its torque 90 degrees would require a different type of mechanism.
Reduction Boxes
- Just as u-joints are usually used when there are slight directional changes in shafts, reduction boxes are usually used when there are large directional changes -- up to 90 degrees. Reduction boxes facilitate major changes in direction usually with beveled gears. They continue the rotation of shafts through changes in direction. Also, they increase or decrease speed at which the shafts turn. While reduction boxes are always shaft couplings, they don't necessarily have to change the shafts' speeds.
Flexible Materials
- Most shaft couplings are made from inflexible materials, which ride on bearings, and they are used to couple two non-flexible shafts. But some shafts are flexible. Rather than using a u-joint or reduction box to change direction, the shaft itself is flexible, like the shaft in a motorized weed trimmer. The concept of a flexible shaft can be used where a flexible section is spliced into two inflexible sections to act as a u-joint. For example, if you joined two sections of a one-quarter-inch solid shaft with slightly smaller rubber hosing, the flexible rubber would couple the two and allow for some bending. The concept can be applied in many ways.

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