Accurate Measurement Practices

Mount Wachusett College and Wood Digest have teamed up to present a series of college-level wood technology courses. This is the 2nd installment in the series of 12 which discusses measuring tools and how to add, subtract, multiply and divide measurements.

Accurate Measurement Practices
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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.
Mount Wachusett Community College
444 Green Street
Gardner, MA 01440
Ken Hanson
Wood Technologist
Wood Products Workforce
Development Coordinator
Forest and Wood Products Institute
(979) 630-9179
Fax: (979) 630-9554
Student of the Month
NAME: Hongtao Zhou
SCHOOL: Purdue University
PROGRAM: Wood Research Laboratory
MAJOR: Furniture design and manufacturing
GPA: 3.8
AGE: 28
zHow did you become interested in working with wood?
I was born in a small wood production town in northern China. I fell in love with wood while working with my father in his wood architecture business. Although my fingers were nicked many times by knives and saws, the "excellent" woodworks I made increased my interest and motivated me to attend Northeast Forestry University in China. Later, I attended the Purdue Wood Research Laboratory, which provides me with more visions of many interesting wood products and woodworkers.
Where do you look for inspiration?
I think it is anywhere. I am trying to discover new markets, life styles, cultures and technologies all the time. It is enjoyable to think of and try all of the possible new creations. Sometimes, the sparks in a dream are powerful, and they make the design process more exciting.
When wood can make life more beautiful, why not?
How would you describe your style?
My style is a combination of art and technology for a certain market, which maximizes the usage of material and machinery and reaches the best in functionality, profit and sustainability.
I am mainly focusing on population needs and markets. I believe new visions of population, culture, science and technology not only inspire products' forms, but also influence new concepts and new marketing. The new combinations can inspire more exciting ideas for furniture.
What was your latest project?
My last project was an adjustable CNC rocking chair. This project is designed to adapt to a wider range of population sizes with the idea of design for assembly. This design won first place in the ready-to-assemble category in the Design Emphasis Awards at the 2006 International Woodworking Fair in Atlanta.
What are you plans for after graduation?
I plan to be a furniture designer, get deeper and create more products for people's new needs and promote them into markets.
In the long run, it will be good for me to start from industry to business and later to go into education. This allows me to continue tasting the joyfulness in the world of wood from different perspectives and to never leave it.
References used:
Print Reading for Industry by W. Brown and R. Brown



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