Okay you built your new illusion and you’re at the store reading about casters and you realize each caster has a weight rating on it. A common question is what size wheel and weight capacity do I need? The one that throws most people is if a caster has 150 pound capacity, does that mean per caster or does that mean the total project can’t weigh more than 150 pounds? Below I’ll show you how to do that calculation.
You’ll need to first determine the weight of your trick along with your assistant or any loads that may be placed inside the trick to determine the total load for the caster. The other major determination is what type of surface I will be pushing this trick over. This will determine the material and the diameter that you will need in choosing a caster. I can’t urge you enough not to skimp in this area. Especially if you’ll have an assistant loaded in your trick when you push it on or off a stage. That assistant is then trusting you to look after their safety and health while they’re onstage with you. A cheap caster on an illusion that causes the trick to tip over or crash on stage can cause serious injury to the person inside. Remember stages have slants -you need to consider how you will hold the trick in place once it’s onstage as well. There is nothing worse than a deceptive base rolling into the front row of the audience with an assistant inside!
- Wheel Diameter: The nominal diameter of the outside of the wheel, this typically describes the basic size of the caster (i.e. a 5” wheel diameter caster is typically referred to as a 5” caster).
- Swivel Radius: The distance from the center of the fastening to the outer most point of the caster. This specifies the minimum clearance required for a mounted caster to swivel a full 360 degrees.
- Mounting Height: The vertical distance between the bottom of the wheel and the mounting point of the unit.
- Dynamic Load: The load a caster is designed to carry on a continuous basis. Load is assigned on a per caster basis. To determine the load based on the number of casters on a unit, divide the total weight by the number of casters.
For Example: a trick needs to support 400 pounds and will use 4casters.
400 pounds / 4 casters = 100 lb. minimum load rating required per caste
Specifying the Correct Caster
Below is some general information aimed at making selecting the right Shepherd or Bassick caster a little easier.
- How much load capacity will your product require?
Divide the load capacity needed by the number of casters your product will be using. For example, your cart will need to carry 600 pounds and will use 4 casters: 600 pounds / 4 casters = 150 pound load per caster would be sufficient for your cart.
- What wheel size and material would be best for my application?
The best and easiest way to improve rollability is to choose the largest diameter wheel practical for your application. Wheel width must all be taken into consideration- are you going to be rolling over large grating or large thresholds? Selecting a tread material should be based upon the environment your casters will spend majority of their time on. Typically the harder the surface (tile, etc.), the softer the wheel you would want to use for protection. The softer the surface (thick carpet, etc), the harder the wheel you want to use for easy mobility. To the right is a chart detailing which materials are recommended on particular flooring materials.
- What type of fastening should I use?
There are a variety of different fastening methods available to make fastening your casters an easy task. Tube and pipe applications usually work best with stem style, while plate mounts can be mounted on a variety of bases where there is adequate room.
Other Caster Definitions
- Axle: The supporting shaft or member which a wheel or a set of wheels revolves on.
- Bearing: Known as either the swivel bearing raceway or the wheel bearing. Bearings enable a caster to swivel freely, and can also be used for added rollability within a wheel.
- Bolt Holes: The mounting holes on top plate style casters that are used to secure the caster to a product.
- Bore: The center hole of the wheel where an axle passes through.
- Brake: Stops or prevents the movement of the wheel. Various styles of brakes are available for a variety of different applications (i.e. total lock, friction, tread lock, etc.).
- Capacity: (Or Load Capacity) The maximum load per caster or wheel (please note that there are different types of capacity ratings- such as dynamic load rating, impact load rating, and static load rating).
- Caster: A wheel fastened within a mounting rig that is attached to a product in order to provide a mobility solution.
- Direction Lock: When this type of brake is applied, only the swivel section of the caster locks to a rigid straight position to help aid in easy steering.
- Durometer: A measurement of the hardness of the wheel tread.
- Dynamic Load Rating: A load rating that describes the overall capabilities of the caster. The dynamic load rating consists of durability testing at the established rating, 2x the rating in impact testing, and 4x the rating in static load testing. All Shepherd and Bassick casters are rated as a dynamic load.
- Fastening: The method of which a caster is mounted to a product. Typical fastenings include top plates, threaded stems, and grip ring stems.
- Friction Brake: A style of brake that when applied pinches the legs of the horn together to create friction against the wheel hub.
- Horn: The caster parts that comprise legs, plus a base.
- Hub length: The measurement through the bore to each side of the wheel.
- Kingpin: A rivet or threaded bolt that securely holds the mounting plate, bearings, and horn assembly securely together allowing for swivelability.
- Legs: The axle support brackets that extend down from the horn base or mounting plate.
- Offset: (Or Swivel Lead) The perpendicular distance between the vertical centerlines of the king pin and the axle of a swivel caster.
- Overall Height: The vertical distance from the bottom of the wheel to the top of the mounting plate (stem versions measure differently based on the style of stem).
- Rigid: Another term for stationary or fixed caster. The Rigid caster can roll forward or back, but it’s restricted from swiveling 360˚.
- Rig: A swivel or rigid caster assembly less the wheel and axle.
- Rollability: The ease of starting the rolling motion of a caster.
- Stem: A fastening method on the caster used to mount the caster to a product. Typical stems include grip ring stems, threaded stems, grip neck stems, expanding stems, etc.
- Swivel Lock: When applied, it converts a free swiveling caster into a rigid caster scheme.
- Swivel Raceway: Single or double rows of ball bearings which support the swiveling movement of the caster.
- Swivel Radius: Horizontal measurement from the middle of the kingpin to the edge of the wheel.
- Thread Guard: The piece of metal or plastic covering the wheel to prevent dirt, threads, and other debris from attaching to the wheel.
- Total Lock: When this style of brake is applied, it locks both the wheel and swivel of the caster simultaneously.
- Tread Lock Brake: A brake that when applied locks securely down onto the tread of the wheel.
- Wheel Diameter: The nominal diameter of the wheel, this typically describes the basic size of the caster (i.e. a 5” wheel diameter caster is typically referred to as a 5” caster).
- Wheel Tread: The outside material composition on the wheel which rolls directly on the ground.
- Wheel Core: The inside material composition on the wheel in which the tread is formed onto.
- Tread width: The width of the wheel when held upright.
- Yoke: Another term for horn.
Information provided by Shepherd suppliers