•  Close both the acetylene and oxygen regulators by  backing out the adjusting screw counterclockwise  until loose. •  Carefully coil the hose to prevent kinking and store it  to prevent damage to the torch and tip.  The material to be welded, the thickness of the metal, the type  of joint, and the position of the weld dictates the procedure  and technique to be used. When light-gauge metal is welded, the torch is usually held  with the hose draped over the wrist.  [Figure 5-24]  To weld  heavy materials, the more common grip may provide better  control of the torch.  [Figure 5-25] The torch should be held in the most comfortable position that  allows the tip to be in line with the joint to be welded, and  inclined between 30° and 60° from the perpendicular. This  position preheats the edges just ahead of the molten puddle.  The best angle depends on the type of weld, the amount of  preheating required, and the thickness and type of metal.  The thicker the metal, the more vertical the torch must be for  proper heat penetration. The white cone of the flame should  be held about  1 ⁄ 8 -inch from the surface of the metal. Welding can be performed by pointing the torch flame in the  direction that the weld is progressing. This is referred to as  forehand welding, and is the most commonly used method  for lighter tubing and sheet metal. The filler rod is kept ahead  of the tip in the direction the weld is going and is added to  the puddle.  For welding thick metals or heavy plate, a technique called  backhand welding can be used. In this method, the torch  flame is pointed back toward the finished weld and the filler  rod is added between the flame and the weld. This method  provides a greater concentration of heat for welding thicker  metals and would rarely be used in aircraft maintenance.  If the torch is held in the correct position, a small puddle  of molten metal forms. The puddle should be centered in  the joint and composed of equal parts of those pieces being  welded. After the puddle appears, the tip should be moved  in a semicircular arc or circular motion equally between the  pieces to ensure an even distribution of heat. As the metal melts and the puddle forms, filler rod is needed  to replace the metal that flows out from around the joint.  Adding Filler Rod to the Puddle Puddle Figure 5-25.  Hand position for heavy-gauge materials. Gas Welding Procedures and Techniques Figure 5-24.  Hand position for light-gauge materials. 5-15