previous weld deposits before welding over them. Some of  the common types of groove welds performed on butt joints  in the flat position are shown in  Figure 5-36. flat position because of the force of gravity. The molten metal  has the tendency to run down. To control the flow of molten  metal, the voltage and current adjustments of the welding  machine must be correct.  Fillet welds are used to make tee and lap joints. The electrode  should be held at an angle of 45° to the plate surface. The  electrode should be tilted at an angle of about 15° in the  direction of welding. Thin plates should be welded with little  or no weaving motion of the electrode and the weld is made  in one pass. Fillet welding of thicker plates may require two  or more passes using a semicircular weaving motion of the  electrode.  [Figure 5-37] The current setting, or amperage, is less for welding in  the vertical position than for welding in the flat position  for similar size electrodes. Additionally, the current used  for welding upward should be set slightly higher than the  current used for welding downward on the same work piece.  When welding up, hold the electrode 90° to the vertical, and  weld moving the bead upward. Focus on welding the sides  of the joint and the middle takes care of itself. In welding  downward, with the hand below the arc and the electrode  tilted about 15° upward, the weld should move downward.  The procedure for making fillet weld in a lap joint is similar  to that used in the tee joint. The electrode is held at about a  30° angle to the vertical and tilted to an angle of about 15°  in the direction of welding when joining plates of the same  thickness.  [Figure 5-38] Overhead position welding is one of the most difficult in  welding since a very short arc must be constantly maintained  to control the molten metal. The force of gravity tends to  cause the molten metal to drop down or sag from the plate,  so it is important that protective clothing and head gear be  worn at all times when performing overhead welding.  Vertical positing welding includes any weld applied to a  surface inclined more than 45° from the horizontal. Welding  in the vertical position is more difficult than welding in the  For bead welds in an overhead position, the electrode should  be held at an angle of 90° to the base metal. In some cases  where it is desirable to observe the arc and the crater of the  weld, the electrode may be held at an angle of 15° in the  direction of welding.  When making fillet welds on overhead tee or lap joints, a  short arc should be held, and there should be no weaving of  the electrode. The arc motion should be controlled to secure  good penetration to the root of the weld and good fusion to the  plates. If the molten metal becomes too fluid and tends to sag,  the electrode should be whipped away quickly from the center  ahead of the weld to lengthen the arc and allow the metal to  solidify. The electrode should then be returned immediately  to the crater of the weld and the welding continued. Anyone learning or engaged in arc welding should always  have a good view of the weld puddle. Otherwise there is no  way to ensure that the welding is in the joint and keeping  the arc on the leading edge of the puddle. For the best view,  the welder should keep their head off to the side and out of  the fumes so they can see the puddle.  The expansion and contraction of metal is a factor taken into  consideration during the design and manufacturing of all  aircraft. It is equally important to recognize and allow for the  dimensional changes and metal stress that may occur during  any welding process. Expansion and Contraction of Metals Overhead Position Welding Fillet Weld Lap Joint Weld Vertical Position Welding  Figure 5-38.  Typical lap joint fillet weld. Figure 5-37.  Tee joint fillet weld.  $^{1}$/$_{4}$ " Leg size Direction of welding Short arc 45° R o o t o f  w e ld Profile view $^{3}$/$_{8}$" $^{3}$/$_{8}$" 30° 1 2 5-29