Marking-Off Techniques for Metal Fabrication
According to engineer S. K. Garg, there are eight main tools for marking off sheet metal. As well as mastering the use of each of these, metal fabricators need to be capable of careful and precise work to fractions of an inch. Good technique also dictates that metal should be cut as resourcefully as possible so as to avoid waste and unnecessary cost.
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General Technique
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Paint the area of the metal to be marked with marking blue. This blue liquid, a mixture of gentian violet and methylated spirits, will show up your marks more clearly. Mark the metal with a scriber, a pen-like tool with a needle point. It is the equivalent of the carpenter's pencil. You might also use a prick punch, solid punch or center punch to make lines stand out even more or to mark holes to be drilled.
Use the Correct Rule
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Good marking-off techniques depend on excellent measuring. For Garg, there are three main rulers that are of use to the metal fabricator. The first is the 12-inch steel ruler. Use this for small work. Many metal workers carry their 12-inch rulers in a special pocket in their overalls. The folding ruler, as the name suggests, folds up for convenient carrying, and is useful when you are marking-off larger work. Use the steel tape for the largest work.
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Other Tools
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The protractor is available with a functional swinging blade. Use a marking tool called a "straight edge" to mark off straight lines. This is a flat steel bar, available in various lengths. To mark off right angles, use a steel square. This is an "L" shaped tool with a 90-degree angle. The wider part is the steel square is called the "body" and the narrower part is called the "tongue." For other angles, use a swinging blade protractor. For circles and arcs, use dividers or a beam compass.
Patterns
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Sheet metal fabrication expert Eddie Paul is keen on making patterns before beginning any cutting out of metal parts. He suggests you cut these out from paper, card or wood to serve as templates. When you are happy with your pattern, or template, trace it onto your metal as a cutting guide. Expensive mistakes can thereby be avoided. Store all your patterns carefully after use to save time in the future.
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References
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