Why use threaded fasteners at all when building a machine?
Why use bolts at all? Why not just weld everything together? Threaded fasteners are (usually” not permanent. It may seem obvious, but some components need to be able to be removed in order to service the machine. It’s true some amount of permanent assembly methods are present in most machines, and there is a cost balance that needs to be reached between simplicity and serviceability. Welded base frames are made instead of bolting every structural beam together, for example. All automation equipment will need servicing during its life, however, and this process usually requires the removal of exterior guarding, panels, or the like. If the panels were welded or riveted on, this couldn’t be accomplished easily. The added benefit of easily servicing the machine justifies the added cost associated with the purchasing and installation of fasteners.
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Threaded fasteners come in many different sizes but are standardized around only a few “series” which are common in industrial automation. We’ll go more into thread series later, but suffice to say, there are two main ones used in the United States: Unified and Metric. There are many obvious benefits to basing our fastening needs around standardized parts. Firstly, standard clearance and tapped holes can be specified in parts with a high degree of confidence that fabricators will have that drill bit or tap size on the shelf. Second, we can depend on vendors to have those standard sizes in stock to be ordered and readily available. There are plenty of opportunities to prove cleverness in a design, but finding a specialty or obscure thread is not one of them.