Technology and our changing world high Technology

CUTTING EXTERNAL THREADS

1. 
   Grind or file a chamfer (slanted surface across part of an edge) at the end of the stock. This helps to protect the finished thread and aids in starting the die.
   
2. 
   Fit the propei' die in the diestock, with the tapered portion of the die toward the guide collar.
   
3. 
   Fasten thepieceto be threaded in avise. Apply afew dropsofoil.
   
4. 
   With one hand, hold the die over the workpiece. Turn the die to get it started. After the thread has started, apple even pressure to both handles. Turn thedie aboutone complete turn.
   
5. 
   Continue to cut the threads until the desired length is reached. Remove the die and carefully, clear away the chips. Test the piece in the threaded hole.
   

Review question

1. 
   Tell the special use for each of the following fasteners: (a) machine screws,(b) cap screws,(c) machinebolts, and (d) setscrews.
   
2. 
   Why should you notusepliers to tighten nuts and bolts?
   
3. 
   For what is the tap used?
   
4. 
   What tool is used for cutting external threads?
   
5. 
   What is the correct tap drill to use for cutting a A” 20 thread?
   

SOLDERING, BRAZING, AND WELDING
Soldering is joining metal parts with a filler metal, called solder, at temperatures bellow 800°F. Soldering differs from welding in that the metals joined are not actually melted. Because of this, the melting point of the solder mustbe lower than thatof the metal workpieces.
Soldering is not difficult if a few simple rules are followed. First, the metal to be soldered must be clean. Second, a flux must be used. This will prevent oxidation and help lhe flow of the solder. Third, enough heat mustbe applied to melt the solder. Fourth, the correct solder mustbe used for the job.


SOLDERING EQUIPMENT
The following tools to provide heat for soldering are commonly found in the shop:

• 
  Th e so Ider ing copper is heated in a gas furnace.
  
• 
  An electric soldering copper is convenient to use. These coppers range from 50 to 3000 watts. The 200 - watt copper is a good size for most sheet-metal soldering. Small electric soldering guns are also used for electrical work.
  
• 
  A propane torch is used for soldering copper tubing general sheet­metal work.
  

Soft solders for most metals, such as galvanized iron, tin plate, and copper, are made from a combination of tin and lead. They are available in bar and wire forms. A good solder to use is fifty-fifty, or half-and-half, solder which melts at about 414° F. Fluxes are used to keep the metal clean while soldering. They also help the solder spread evenly. Acid flux and rosin paste fluxes aregenerally used. Rosin fluxes mustbeused in electrical work to stop theparts from corroding. Some solder wirehas ahollow core filled with flux.