Thanks to all the feedback I got from my first post, my second will explain the how, why and what of threaded fasteners. Of course, this post will not go into the jargon of types of threads, thread angle and pitch, any wikipedia page will give that information. I will explain the practical use of different machine screws, heads and types.
One of the first design choices we run into in an assembly is to use fasteners or to weld the parts together. This may lead us to answer the "why fasteners." Any two parts that serve some purpose when mated, but need to be disassembled in the future for service or maintenance will have to be fastened by screws, else we can just weld them in most cases. Also when two dissimilar materials need to be fastened, screws come into the picture. Circumstances allowing, I will always have two parts welded to each other to provide a strong, permanent bond.
There is a lot of know-how into using threaded fasteners. Do we use it with or without washers? What is the use of machine screws with built in flange-like washers. How do we use self-clinching nuts? In order to reduce assembly time, I have always used self-clinching nuts and screws with built-in washers. In most cases, I use a washer to use my screw on an oversized hole (I sometimes use oversized holes to widen tolerances and reduce manufacturing costs). Of course, washers are inevitable when steel screws are used over softer materials like aluminum and copper.
The drive of the screw is very important. I have always avoided using a slotted screw driver because it is difficult to get a continuous drive and the driver always tends to slip. My first preference would be a hex-socket headed screw because this provides the maximum grip to tighten with an allen key. Second preference would be Philip-headed screws. The tools to tighten these are also widely available when compared to torx or other drive types. And I will try my best to use the same type and size of screw in an entire assembly for obvious reasons like standardization and time saving.
No comments:
Post a Comment