What should be the motion used during preheating to ensure uniform heating?

Using a slow, constant, circular sweeping motion during preheating ensures uniform heating across the entire area of the joint being brazed. This technique helps distribute the heat evenly, which is critical for achieving optimal brazing conditions. By moving in a circular pattern, you can effectively avoid hotspots that may occur with more linear or erratic movements, which could lead to uneven temperature distribution.

Uniform heating is vital as it allows the filler metal to flow smoothly into the joint without being hindered by thermal stresses or variations in material temperature, which can affect the strength and integrity of the bond. This method also helps prevent overheating certain areas, which could cause warping or damage to the parts being brazed. Therefore, the circular sweeping motion is the best choice for ensuring consistent and effective preheating.