Part Four: The Screw Thread Solution

So far in Fixing Fasteners, we’ve provided a short introduction to screw threads and threaded fasteners, along with some options for making them stay put. Part Three described one of the most efficient systems for accomplishing this, the Detroit Tool Company's wedge ramp thread design. The patent for that simple yet ingenious invention has long since run out and is now represented by two companies—Stanley Engineered Products with its Spiralock^TM brand and its alternative, Emuge-Franken’s Self-Lock™ thread locking technology.

Part Three: A Valiant Attempt

In the previous two segments of Fixing Fasteners, we reviewed the basics of thread design and provided some brief descriptions of the industry's various attempts to secure fasteners. This section will discuss a more practical approach to the latter. In 1979, the Detroit Tool Company made a simple modification to a standard thread profile. They called it Spiralock^TM, and it soon became quite popular for use in mission-critical applications by military and aerospace manufacturers, and eventually the medical industry.

Part Two: As the Screw Turns

In Part One of Fixing Fasteners, we offered a brief overview of screws and thread manufacturing, their different classes of fit, and some comments on the importance of proper tolerancing and gaging when machining screw threads. Adhering to these guidelines is the first step toward making strong, dependable fasteners. However, even the highest quality screw, nut, or bolt can come loose unexpectedly (often at the worst possible time) when subjected to vibration and other forces.

That's because threaded fasteners are intended to come apart. It’s an unfortunate truth (or a fortunate one, depending on your perspective) that all machinery and other mechanical assemblies must be constructed in a manner that allows them to be serviced, refilled, and repaired. If not, they could simply be welded together, eliminating the need for threads entirely.

Part One: Threads on Parade

This four-part series will discuss threaded fasteners, why they come loose, and how engineers and product designers can prevent this unfortunate, sometimes dangerous event. We’ll preface it by saying that Emuge-Franken is a cutting tool manufacturer with more than a century of experience in this area. The company invented the first spiral point tap for producing internal threads in 1921 and has since developed some of the highest-quality drills, end mills, and threading products on the market. As you’ll soon see, they have also addressed the problem just mentioned—fasteners coming loose—with a comprehensive and innovative solution.

In PartOne of this article, I presented some reasons why shops should consider material-specific taps. This section will explore some of the features to look for in one. Before diving in, however, it’s essential to recognize the difference between plug and bottoming taps.

Drilling has long been recognized as one of the most common yet most challenging of all metalworking operations. Tapping is even tougher. Aside from problems with chip evacuation and potential coolant starvation, there's the sheer amount of metal being removed relative to the available space for the cutting tool.