208 Welding Print Reading With the exception of height, which is optional, no other back or backing weld dimensions are shown with the weld symbol, Figure 16-23. If other dimen- sions are required, they are shown on the drawing. A melt-through weld assures full joint penetra- tion. The melt-through weld symbol is similar to the back or backing weld symbol with the bead filled in as shown in Figure 16-24. A dimension to the left of the symbol specifies the amount of melt-through. Backing, Joint Spacers, and Runoff Weld Tabs Backing is material placed against the back side of a joint to withstand molten weld metal, as shown in Figure 16-25. It is employed when full penetration groove welds are required and welding can only be done from one side. Backing is thoroughly penetrated by the weld and usually left in place. Figure 16-22. A symbol added above the flush contour symbol identifies the mechanical method used to finish the weld flush. M NOTE 2 Backing weld machined flush with base metal Desired welds Symbol Figure 16-23. Only the back or backing weld height dimension is shown on the welding symbol. If other dimensions are needed, they are given elsewhere on the print. Desired weld Symbol 1 16 1 16 Figure 16-24. The melt-through weld symbol resembles the back or backing weld symbol, but the bead is filled in. The height of root reinforcement may appear as a dimension specified to the left of the melt-through symbol. (American Welding Society) Desired weld Symbol 1 8 1 8 Figure 16-25. Backing used in a joint. A specification indicating its use is shown in the tail of the reference line. Backing Desired weld Symbol B-3 Figure 16-21. A flush contour symbol indicates the weld is to be finished approximately flush with the base metal. Desired welds Symbol NOTE 1 Weld deposited flush with base metal Figure 16-20. Specifications for a back weld. A note in the tail of the reference line indicates whether to make a back or backing weld. NOTE- 1. GROOVE WELD MADE BEFORE WELDING OTHER SIDE. 2. (ABOVE FOUND ELSEWHERE ON PRINT) Desired welds Back weld Symbol NOTE 1