Vocabulary Items
Being able to measure accurately is an important skill for anyone who reads and uses blueprints in all the metals trades like welding or machine tool technology. This part of the lesson reviews the basic rules of measurement. Some students may not have had many chances to measure things carefully before, so these exercises will give them the practice they need. Other students, who have more experience, can still use these activities as a helpful review.
No matter your experience level, there is one very important rule when taking measurements from a print: Do not measure the actual paper print if a dimension is missing or hard to read. Prints can shrink, stretch, or be printed at the wrong scale. If you measure the drawing itself, you may end up with measurements that are completely wrong. Always look for the written dimensions on the print or ask your supervisor if something is unclear.
Understanding Scale Measurement
A drawing can be the same size as the real object (full size), or it can be drawn larger or smaller. Most of the time, if it is not full size, the drawing is made smaller. This makes the blueprint easier to handle and read. For example, no one wants to carry around a full‑size drawing of something huge, like a rail car. On the other hand, if the object is very small—like a tiny machine gear—it may be easier to draw it larger so you can see the details.
Different types of work use different scales. For example, a metal part might be drawn at half size (½″ on paper equals 1″ in real life). A large structure might use ¼″ = 1′‑0″, which means the real object is 48 times larger than the drawing. Maps, buildings, and mechanical parts all use different scales depending on how big the real object is and how much detail is needed.
There are many scales used in different trades. Welders and machinists often see certain scales again and again, so it is helpful to practice reading them. Understanding scale will make blueprint reading easier and help you read welding drawings more accurately.
Full Scale (1″=1″, 1:1)
Full scale is simply letting one inch on a ruler, steel rule, or draftsman’s scale equal one inch on the actual object. Rules of this kind are usually divided into 1 /16” or 1 /32” units. The first measurement exercise will be with full size. If you can measure accurately in full scale, you may want to skip ahead.
Measurement practice
Here is a “big Inch”. Each space equals 1/32”. If you have not worked with accurate measurement, spend some time studying it.
Locate the given fractions.
Directions:
Each of the fractions below is numbered. Write that number above the scale and point with an arrow where the fraction is located. Number 1 has been completed. Click on the image below to get a copy to print.
Scaling Up
Half Size (1/2″ = 1″, 1/2:1)
The idea of half size measurements on a drawing is a unit, such as 1/2” on the drawing, represent a larger unit such as 1” on the part. If the drawing is properly labeled, the words HALF SIZE or 1/2″= 1″ will appear in the title block.
Using a Special Half-Size Rule
Using the half-size scale is not difficult, but it does take some practice. When you use this special type of rule, read it from right to left (<–). To measure a distance of 2-3/16” you look first for the 2, then go backwards (to the left) to the zero and count off another 3/16 on the fraction tick marks. You measure this way for each dimension that has a fraction. Whole numbers (numbers without fractions) are measured in the usual way.
Practice with half-size rule (optional)
Next, locate a half size scale. Measure the lines· below to the nearest 1 /16 of an inch. Write the length of the line in the space provided. Click the image to get a copy to print.
Because paper is dimensionally unstable due to humidity, exact answers to this half size measurement practice cannot be given. That is another reminder that it’s poor practice to measure from a piece of paper.
Quarter Size
Quarter size is used and read in a similar way to half size except that each unit, such as a quarter of an inch, represents a larger unit, such as one inch. If the drawing is properly labeled the words QUARTER SIZE, QUARTER.SCALE, or 1/4″ = 1″ will appear in the title block.
Using a Special Quarter-Size Rule
The quarter size scale is used in a similar manner as the half size scale.
Practice with quarter size rules (optional)
For quarter size practice, use a ¼”=1” scale, if available. Draw lines in the area provided to the required length. Have another student or the lab instructor check your lines for accuracy.
Practice Quiz
For this quiz, you will be given an object to measure with a ruler or tape measure. You will record measurements in full scale and then draw each length in ½ and ¼ scale.
Questions
