Technology and our changing world high Technology

Using files
Follow these suggestions when using files.

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  Be sure to have a handle on the file, for safety.
  
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  Keep the file clean with a file card or brush. This will keep the file from gouging and scratching the workpiece.
  
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  Whenever possible, mount the workpiece in a vise. This makes filing easy, safer, and more accurate.
  

Abrasives
An abrasive is a hard substance used to wear away a softer material. Abrasives are crushed into small grains having sharp cutting edges. Each grain of abrasive is actually a cutting tool like a saw or chisel. These abrasive grains are used to make grinding wheels. They are also glued to belts, discs, and sheets to form metal-cutting “sandpaper”. These are called coated abrasives.
USING THE GRINDER
Hand grinding includes the rough shaping of metal pieces and the sharpening of small tools. The hand grinding of steel parts of tools is usually done on a bardı or floor grinder. In many shops there are two machines. These machines are a small bench grinder for tool grinding only and a larger, floor-type grinder for general purpose work.
To use the grinder, hold the metal firmly against the tool rest. Then press the metal against the revolving wheel. Move it back and forth across the wheel face so that the grinding is done evenly. To round an end, hold the metal on lhetoolrest. Move the back of he metal in an arc while keeping the end to berounded in contactwith thewheel.
When grinding points and edges of tools, check frequently to be sure they hold the right shape. Use a gauge to check this. Correct shapes of common tools are shown in this book. When sharpening chisels, remember to grind the “mushroom” heads.
Polishing and buffing operations
Polishing is done on a belt or disc sanding machine. Be sure that the machine is set up for polishing metal, and not for sanding wood. Number 40 (coarse), No 80 (medium), or No 120 (fine) grit abrasives are generally used. When using the polishing machine, wear goggles. Touch the workpiece gently to the belt or disc. Do not overheat the metal. Hand polishing can also be done with abrasive paper.
Buffing is done by holding the work against a flexible wheel. Fine abrasive materials have been applied to the wheel, using glue or some other material as abinder. Plated objects and nonferrous metals areoften buffed.
A buffing machine is shown in. Buffing wheels are made of stitched pieces of cotton, muslin, chamois, or flannel. Buffing compounds are bars of emery, Tripoli, rouge, pumice, rottenstone, and whiting.
Apply the compound to the wheel as it is rotating. Press the bar or stick of compound lightly on the wheel until the entire edge is treated. Hold the article to be buffed in a slanting position. Press it lightly against the wheel. Move itback and forth and up and down until thedesired finish is obtained.