Fig. 77.--Burning Upright Joint
Fig. 78.--Branch Joint Ready for Burning
The seams should not be soiled or greased, and care must be taken not to tarnish them in any way. If the lead is not shaved quite clean, or it becomes tarnished after it is shaved, it will be found difficult to burn it together successfully. No tallow or smudge is necessary. The operator will soon detect the presence of any foreign substance or dirt on the lead, and the shavehook should be kept handy to remove it.
In burning a vertical lapped seam, starting at the bottom, the lapping lead is melted, and as it runs is turned on to the back portion and fused into it. A slight projection is formed, which holds the next melting, and so on, each layer forming a base for the next, and adding to the height until the top is reached.
In practising either horizontal or vertical burning, the student should first place his work at an easy angle—say, at about 25° or 30°—gradually raising it as he becomes proficient until the seam is in a horizontal or vertical position as desired. Two surfaces can be burned together in any position—horizontal, vertical, or even overhead, where soldering would be impossible.
Pipe joints can also be made by burning. First one pipe is opened to form a socket like a slip joint. The male part, which must enter at least 3⁄4 in., must be well shaved and made to fit tight. [Fig. 77] shows an upright joint prepared and partly burnt. [Fig. 78] shows a section of a branch joint as prepared for burning. Care must be taken to work up a good thick shoulder for the socket N.