Problem
Hedge trimmer blades were loosening over time and use. On earlier models of hedge trimmers, the cutter blade's retaining bar assembly was attached to the stationary bar with five machine screws and corresponding nuts. These nuts were crimped for locking action, and a spacing washer was placed between the stationary bar and the retaining bar to allow the cutter bar to reciprocate.
Over time, however, the continuous vibration of the trimmer loosened the assembly of the machine screw and crimped nut. The blades would separate, and the trimmer would no longer cut efficiently.
Also, to sharpen the trimmer blade the screw and nut had to be disassembled. Once disassembled, the crimped nut lost most of its locking ability. This led to even quicker vibrational loosening of the trimmer blade after reassembly.
Solution
The trimmer blade assembly was redesigned to incorporate five TAPTITE® screws driven directly into pilot holes in the steel stationary bar of the trimmer. The inherent locking action of these thread forming TAPTITE® screws eliminated the vibrational issues present in the old machine screw/nut design. The product now performed as expected, insuring efficient cutting over time.
The hedge trimmer blade represents an excellent application of TAPTITE® thread rolling screws. Break-away and prevailing back off torques of TAPTITE®screws are higher and more consistent than those of machine screws with crimped nuts. In this type of application, TAPTITE® screws provide an excellent strip-to-drive ratio of 5 to 1, which solved the vibrational loosening problem for this manufacturer.
But the product benefits didn't stop there. In the improved design, the old crimped nut assembly was eliminated altogether, as TAPTITE® screws form their own threads in the stationary retaining bar and don't require a separate nut. The customer realized large cost savings in fewer required parts and reduced assembly time.
The same TAPTITE® screws can be also reinstalled when the blades are serviced without losing any of their original locking ability. This makes the sharpening process easier, and increases the usable lifespan of the tool.