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In manufacturing, accurate measurement practices are the lifeblood of business. We must know how to use several different types of measuring devices, and then know how to write, add, subtract, multiply and divide the numbers. For example, a reader needs to know the length of an object and the print may have only the following numbers:
2 1/4 + 5/8 + 5/16 + 17/32 + 5 19/64 = 2 16/64 + 40/64 + 20/64 + 34/64 + 5 19/64 = 7 129/64 or 9 1/64
Calculators will truly help, but may not be handy. When adding, the first thing we must do is find the common denominator. The denominator is the bottom number of a fraction. A common denominator is the number that all of the denominators divide into. In the above example, the common denominator is 64. Therefore, the equivalent fraction to 2 1/4 is 2 16/64. After using the same process to each number, the answer to this problem is 9 1/64.
When subtracting fractions, determine the common denominator, and then subtract the numerator (the top number in the fraction).
To multiply fractions, simply multiply the numerators and then multiply the denominators. An example of this is:
3/4 x 7/8 = 21/32
Using the same numbers, division requires us to reciprocate the second fraction and then multiply. For example:
3/4 ÷ 7/8 = 3/4 x 8/7 = 24/28 or 6/7 (always reduce numbers to their lowest forms)
To convert a fraction to a decimal number, divide the numerator by the denominator. In the last example, the decimal equivalent of 6/7 is .857 if rounded off to the thousandths. This also can be called eight hundred fifty-seven thousandths.
Published charts offer simple and handy conversions of fraction to decimal, metric, drill and tap sizes, and a host of others. Without the chart, 1 in. equals 25.4 millimeters (mm). To convert a standard measurement into millimeters (metric), multiply it by 25.4. For example, 6/7 x 25.4 = 21.771mm.
The above is meant to be a review for most, but also a reminder that math in one form or another is used every day in the wood products field. Measurements are taken or calculated using a variety of tools from the simple ruler or a tape measure to digital calipers or micrometers. (http://www.starrett.com)
Using measuring devices is a skill that is learned with practice. It is best to take a few measurements along a board to determine if the thickness or width varies. If it does, it will help you troubleshoot a problem with the setup of a machine or sharpness of your tool. Consistent measuring practices is essential not only for determining length and width, but also for thickness, depth of cut, angles, recesses, contours and diameters (inside and outside).
SCALE
The term scale has multiple meanings. In one form, a scale is a measuring device. When reading blueprints, a scaled print refers to a large item that is drawn smaller or "scaled down" incrementally. In this reference, a scale of "½" means that a drawing is produced half scale or one-half the physical size of the object. Conversely, a scale of "2/1" will double the drawn size of small object to make fine detail larger. This may be referred to double scale. Scale may also be referred to as 1" = 1" (full scale) or 1" = 2" or 2" = 1". The units of measurement (in this example inches) may be feet, yards, miles, millimeters, meters, etc., as determined by the print. Be very careful to understand the scale so the finished size is produced. A drawing may also be made to a "No Scale." This may be a print that has been modified on a copy machine or to show three-dimensional general shape. A mechanical engineer's scale or ruler is very helpful to hand draw an object to half scale, quarter scale, three-eighths scale, etc. (http://www.artstuff.net/pacific_arc_mechanical_engineers_tri_scales.htm)
Civil engineering scales, architect's scales, metric scales are other devices used by engineers to accurately draw objects by hand on paper. The textbook used in this course, Print Reading for Industry, by W. C. Brown and R. K. Brown covers this material nicely, with appropriate graphics and descriptions.
TITLE BLOCK
The scale notation on a print is located in the title block, a template location on a print. Typically located in the lower right-hand corner of a print, the title block is the location for information such as the name of the part, part number, drawing number, company name, reference numbers, quality control initials, sheet numbers, materials, and possible many other items of information.
LINES
When reading prints, a line is not just a line. Thickness and shape of a line will provide useful information that will show size, location, centers and interior shapes of hidden features not seen from the outside of a part. The first line to know is the visible line or object line. Typically thicker, this line will define the edges or surface detail of an object.
A hidden line, as the name implies shows the detail of interior components such as a hole through the center of an object. Hidden lines are used only when clarification of interior locations are needed and should not be duplicated if too many lines will confuse the reader.
Never to be confused with object lines, extension lines are thinner and are usually drawn outside the object and associated with a number or dimension. Extension lines show the extent of the dimension and the dimension lines are finished with arrows or slashes as they intersect the extension lines.
The phantom line is not used very often and may be confused with a hidden line, although they have very different uses. A phantom line is used to show movement of parts within a part. For example, a draftsperson may want to show the movement of a roll-top desk or movement of a hinged seat in a bench storage unit. There are other uses for a phantom line, but this is its main use. Next month, we will continue this discussion of line types and focus in on geometric shapes
TRY IT YOURSELF!
To all readers and students: To explore the discussion topics above, you can follow along at home or at work. For enrolled students: As part of your homework, write a one-page paper about the use and care of a measuring device used in your employment. A bulleted chronological list is acceptable. Try surfing the Net using phrases or terms from this article. If you find technical information, please let the class know about them on Blackboards Discussion Board or e-mail to me.