How to reduce the costs of driving screws

In any screw-driven assembly operation, there are three basic components to be considered to ensure the correct joint is effectively and efficiently achieved: the fastener being used, the screwdriver being used, and the bit used in the screwdriver.

It is this third element that is often overlooked in the planning process, but it is also the one element that represents a repeating cost to the process, as it is a consumable.

There are typically two major complaints regarding screwdriver bits, and that is either that they break too soon or they wear out too soon. By doing a bit of analysis of the particular application, it is possible to choose the best tool for the job, and choosing one that is harder is not always the better choice.

By choosing the right bit for the application, it is possible to generate some significant cost savings in the assembly process.

“Through the application of recently developed bit technology, such as the Wera BiTorsion system, it is possible to reduce the effective cost per fastening, even when the cost per bit may be higher,” says Ian Parkhill, president of Wera Tools in North America. “Like anything else, you get what you pay for in screwdriver bits too, and manufacturers that will invest a bit of time to evaluate their applications, and the products available to help them work more effectively, will be much better served in the long run.”

Generally there are two different types of screw-fastened joints; a hard and a soft joint.

In the case of the hard joint, there is very little resistance against the fastener (and the bit), until the fastener seats against the surface being joined. At this time, there is a significant stress put on to the tip of the bit, as the screw wants to stop, and the screwdriver continues to deliver the ultimate torque required. Although it might sound strange, in this case a bit that has some give to it could possibly last longer than a harder bit in the same application.

On the other hand, with a soft joint, this is often a self-tapping application, where the fastener is cutting its way through the material. There is no final torque peak in this case. However, the overall stress placed on the bit throughout the fastening cycle is considerably higher. As a result, even though this is often the case when driving into softer materials such as wood, a harder bit can offer superior durability and performance.

Newer technologies now available in screwdriver bits can actually combine different hardness levels into a single bit, placing a tougher material at the drive end and at the tip, while at the same time providing some give in the centre. This multiple hardness capability, combined with the use of cylindrical-shaped instead of hexagonal-shaped shanks, help to absorb the stresses normally placed on the tip of a bit in the softer centre, almost acting like a shock absorber.

The result is a bit that lasts longer when properly matched to the application, and a reduction in consumable bit costs to anyone involved with high-volume screwdriver assembly operations.

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