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Can it be true that a larger weld may actually result in a weaker connection? As strange as it may seem, the answer is yes. Listen to the "tale of two welds."
A manufacturer of presses decided to build a new, larger model with twice the capacity of anything they had ever produced. The new press required larger shafts, bigger gears, and greater horsepower, and involved more torque. Everything about it was bigger than before. Everyone in the company agreed that every part of this new unit would have to be robust enough to reliably handle all the increased loads, including the increased torsional loads transmitted through a shaft to a gear.
The standard model that the manufacturer had been turning out for years featured a shaft joined to a gear with a simple fillet weld around its circumference, and this design worked successfully in the past. The new model required increasing the diameter of the shaft to 4 in. Initially, the design engineer specified a 1 in. fillet weld to join the shaft to the gear (Figures 1 and 2). As a precautionary measure, the engineer decided...