Using a directional lock or total lock on your casters can be ideal in many applications. The directional lock provides the ability to swivel any of your casters and then lock them into a rigid position when desired to help increase the ease of steering on the unit you are pushing. The total lock brake provides you with the ability to securely lock your casters on the wheel and the caster raceway making your cart completely stationary. However, a situation we disagree with where we see many total locks and directional locks in use is on a stem caster. Using a stem mount on your casters is popular in a hospital or medical setting(along with many others) and is where we have seen challenges arise with this application.
Grip ring Stems, Threaded Stems and Expansion Stems are three common stem styles were this downgraded performance can occur. All of these stems are individually designed for their unique function but they all have one thing in common – they are round. The challenge with having a directional lock or total lock used with a round stem is that the stem can rotate within the mounting hole. There is nothing to secure the stem in a fixed position in the mounting hole which creates the risk of the caster stem moving out of alignment inside the hole. This can be a huge issue when using a directional lock.
The directional lock ensures that the caster(s) will lock into position to guide the cart in a straight line but in order for that to happen, the caster alignment needs to match up exactly with the direction of the rigid casters. Since these stems have the possibility of rotating in the mounting hole, there is no way to guarantee the direction of the caster alignment which can decrease the performance of your cart. If the caster rotates out of alignment you run the risk of flat spotting your wheel and increasing the need for maintenance on the cart. This rotation can occur with any of these stem styles.
The total lock ensures that a caster will be securely fixed when the brake is locked in place since neither the wheel or the caster raceway will be able to turn. If pressure is put on the cart to move while the brake is activated there will be force put on the mounting area of the caster. Since the stems are not horizontally fixed in the mounting hole the casters have the possibility of rotating which could allow the cart to move slightly. Depending on the application this could be an issue and if this occurs over time it could become worse and easier for the casters to move out of alignment over time.
With all this being said, there are definitely many carts and applications that use a directional lock or total lock with a stem mount on the casters. We are not saying it can’t be done. All we want to do is make you aware of the issues that can arise with this application so you take note on the downgraded performance associated. Total lock and directional lock casters being are fantastic options for many carts so always ask your caster expert if these are the right option for your application.