In order to ensure that an acme lead screw serves a particular application correctly, there are a variety of factors that need to be considered. In fact, there are four primary things to consider when it comes to lead screw selection: load, speed, length of travel and end fixity.
In order to ensure that an acme lead screw serves a particular application correctly, there are a variety of factors that need to be considered. In fact, there are four primary things to consider when it comes to lead screw selection: load, speed, length of travel and end fixity. In this article we are going to take a closer look at end fixity and how it relates to the proper mounting of your lead screw assemblies.
For the purpose of this discussion, we will define end fixity as the method by which the ends of the acme lead screw are supported within a given linear motion application.
There are many options for lead screw mounting and it is impractical to cover them all in a single post. So in this article, we'll cover four of the most used combinations of end mounting. As an overview, there are four basic types of end fixity:
Each combination affects the rigidity of the system, which in turn affects the speed at which the system can run and the load capacity of the system. When a system has a high rigidity, it is able to operate at higher speeds and handle larger load capacities. The descriptions and illustrations below are listed in order of the lowest rigidity to the highest rigidity.
Fixed/Free: One end supported with a double bearing and the other end is free.
NOTE: Not recommended for any application other than short travels and slow speeds.
Simple/Simple: Both ends supported with a single bearing.
Fixed/Simple: One end supported with a double bearing and the other end supported with a single bearing.
Fixed/Fixed: Both ends supported with a double bearing.
NOTE: When supporting both ends of a screw with double bearings, the screw is highly ridged and extra care should be taken to ensure compliance in the assembly design.
CAUTION: When using fixed bearing mounts on both ends, contact a Helix Engineer to determine the mount-to-mount length tolerance of the final assembly.As we discussed in the beginning, the type of acme lead screw that you'll need depends upon a variety of different variables, including load, speed, length and end fixity. All of these variables are somewhat related to the other. For instance, in the example given above where we depicted an assembly with one end mounted and one end free, the potential speed and length of this assembly is directly related to the use of this mounting style. Choosing this option would only accommodate an application where travel distance is minimal and the speed of travel is slow. It's important to consider all of the variables within any application and to consult with the experts before deciding on mounting options if needed. Failure to do so could result in a lead screw assembly that just doesn't stack up - and that is an issue that you surely don't want to encounter.
As always, feel free to contact us with any questions.