Chapter 4: Metrology
Overview
The US Secret Service works to combat the industry of counterfeiting money. One of the strategies utilized in identifying fake money is visual identification. By inspecting authentic paper bills, the agent develops a keen eye for specific details. With repetition, the agent’s skills become so refined that when a counterfeit bill is encountered, the agent can spot the fake immediately. The experienced machinist becomes conditioned in the same manner. A major skill mastered by all machinists is measuring and evaluating dimensions or the size of a feature called out on a print. It is not uncommon for a machinist to look at a feature and be able to give you a very close approximation of its size. This skill is often referred to as using the “eyecrometer” to measure.
One of the main tasks in manufacturing a part is measuring the finished part. Engineers develop parts that perform under specific tolerances. When a part is made, machinists must measure and record dimensions for further verification. There are a variety of tools used to inspect and measure a part, and machinists must learn the skills necessary to use these.
This chapter will begin your journey toward mastering the art of precision measurement. This journey begins with a basic understanding of measurement principles.
Objectives
- Identify information in an engineer drawing that is used to verify part dimensions.
- Perform basic arithmetic to identify the tolerance of a given dimension.
- Work with measurements in fractions and decimals.
- Select the correct measuring equipment for a specific task.
- Distinguish the difference between gages, indicators, and direct reporting measurement equipment.
Key Terms
- Accuracy
- Bore
- Decimal place
- Direct read measurement equipment
- Gage
- Go/No-Go Gage
- Inside dimension
- Inspection standard
- Micrometer
- Outside dimension
- Precision
- Resolution
- Slide caliper
- The 10X rule
- Whole numbers
Attributions
the numerical value assigned to a part size, shape or feature.
