Two of the most commonly asked questions about fasteners are “When should fine-thread fasteners be used?” and “Is it preferable to apply torque to the nut rather than the bolt head?” Many different factors influence those decisions, but here are some basic answers to both questions.
As with most endeavors where success can’t be measured by keeping score, a good job of engineering is often defined by not doing a bad job. In other words, the most direct measurement of successful joint design and assembly is a lack of joint problems. Here’s a brief look at the most common reasons why problems occur during joint design, joint assembly and troubleshooting.
The nut factor, as defined in the equation T=KDF, is not derived from engineering principles. Instead, it is arrived at experimentally to make the equation valid.
Installation torque is one of the most common points of assembly discussion between design engineers and manufacturing engineers. However, the most widely held misconception is that joint integrity is determined by applying the right torque.
Studies of fastening costs are generally only valid for an existing design and don't predict the potential costs savings in changing designs. Cost-reduction efforts should focus on three areas: significant product redesigns; superficial design changes; and assembly labor reduction.
Few aspects of threaded fasteners generate an argument as quickly as the use and selection of locking methods. While there is no shortage of locking methods on the market to supplement resisting forces and maintain clamp load, three methods are commonly used by manufacturing engineers.
Less than half of all engineered products undergo any specific joint testing before introduction. While there are exceptions to every rule, this is usually a big mistake. However, before proceeding, it's always a good idea to ensure that test conditions are consistent with production realities.
