In our previous ‘Caster Basics’ post, we talked about wheels. Now it’s time to learn more about the other element that makes a caster a caster: the rig. Also called a fork or horn, the rig holds the wheel in place. While that may seem basic, there are many important things to consider when choosing a rig for your casters. Does the item you’re moving need to turn? How much does it weigh? What conditions will it be exposed to? Will your item be moved manually or by power?
While rigs are traditionally made of steel, they are also available in stainless steel. Stainless rigs are recommended for applications where the caster will frequently be exposed to cleaning agents, steam, caustic solutions or other corrosives that could cause the rig to rust – typically medical and food processing facilities.
Rigs also come in two forms: rigid and swivel. Casters with swivel rigs allow the wheel to rotate and turn in 360 degrees, allowing the object it is attached to also turn. Casters with rigid rigs are just that – rigid. They limit movement to a straight line.
When it comes to racks, carts or other items that are frequently moved around facilities, it’s a safe bet that they include swivel casters. Think of a shopping cart – the two casters at the front of the cart are swivel casters, which allow you to easily turn the cart. The wheel in a swivel caster is usually offset from the vertical axis of the caster to enable the wheel to follow behind the direction of movement. Swivel rigs are available with kingpins, or kingpinless design.
Swivel casters with a kingpin include a rivet or nut & bolt that ties the fork to the top plate, but still allows the rig to rotate. Kingpins allow slightly more ‘give’ in the caster’s assembly, which can lead to a shimmy and increased wear in the caster. The kingpin is also a common point of failure in swivel casters, so it’s important to keep load capacity and how your cart is being moved in mind when choosing a caster with a kingpin.
For heavier loads or use of powered equipment, kingpinless casters are a better choice. On kingpinless casters, the yoke and top plate are tied together with a single race of ball bearings. This eliminates the need for a kingpin, making these casters less likely to fail while also helping to reduce caster ‘shimmy’.
Rigid rigs hold the wheel in a stationary position so it can not change direction, limiting the direction of movement to a straight line. Staying with the shopping cart example, the rear wheels of the cart are rigid. They help maintain the orientation of the cart. If all four wheels swiveled, the cart would be very hard to control, especially with a load of groceries. If all four were rigid, it would be nearly impossible to turn the cart.
Since there are no moving parts in the rig due to no bearings or a kingpin, the rig is virtually maintenance free.
Choosing the correct rig depends on the specific application. If you’re looking to only move things in one direction, a rigid caster would work best. For carts, racks or other things that need to be able to turn, swivel casters – with either a kingpin or kingpinless design, depending on the load – are necessary. Need help choosing the correct caster? Reach out to us. Our experts will help you find the right caster for your needs.