Precision Tools of the Trade: Linear Measurement Equipment
During all aspects of design engineering, it is critical to ask how the design will be manufactured. “precision tools of the trade” explores manufacturing through the tools used to inspect and monitor designs as a part or assembly moves through an engineering process. Knowing the tools available to the 3rd party companies responsible for manufacturing your product will help you understand how pricing can dramatically increase based on the communicated GD&T requirements posed.
Linear refers to a dimension along a datum plane or perpendicular to a datum plan. Small precision linear equipment is used for incremental measurement of shaft diameter, root diameter, thickness, feature to feature dimension, groove measurement, depth of a feature, squareness, and more. They are utilized for in progress verification as well as quality control between engineering processes.
Measurement equipment is labeled with accuracy and resolution, these are commonly misinterpreted. The resolution is simply the smallest incremental reading available on the measuring tool, whereas accuracy will vary based on how the tool is used. Mitutoyo and other precision measurement manufacturing companies have developed comprehensive documentation outlining error mitigation while inspecting. This is a link to a Mitutoyo PDF document titled: Quick Guide to Precision Measuring Instruments
Calipers are available in the Vernier scale, dial, and digital. Calipers are useful and most accurate for linear point to point measurements over small distances. Longer calipers are available, but will decrease in nominal accuracy and pose greater risk for measurement error. Physical limitations including flat measurement faces make hole measurements error prone (or require additional geometry to determine the error present).
Mitutoyo Digital Caliper
Starrett Dial Caliper
Fowler Vernier Caliper
The micrometer is one of the highest resolution tools available for small feature measurement. Micrometers are available in incremental sizes in order to maximize resolution. The measuring head can be dynamic, including: spline micrometers, point micrometers, v-anvil micrometers, disk micrometers, gear tooth micrometers, and many more.
Mitutoyo Digital Micrometer
Fowler Digit Counter Disc Micrometer
Mitutoyo V-Anvil Micrometer
The height gauge is a stationary tool used to measure the vertical dimension of a feature. It is intended to be used in a controlled environment on a level surface to remove as many error factors as possible. The head of the gauge can be replaced to accommodate flat or round surfaces, a dial indicator for higher precision measurements, counterbores, and more.
Starrett Digital Height Gauge
Mitutoyo Digital Height Gauge
Depth Gauges and Micrometers
Depth gauges are used to measure the depth of a feature more precisely than a caliper attached depth gauge. Best used on a bore feature perpendicular to a flat surface, the depth gauge’s scale will physically move into the hole or bore as the “arms” rest on the surface. Some depth gauges and micrometers have replaceable extension rods to cater to the application.
Fowler Vernier Scale Depth Gauge
Mitutoyo Digital Depth Gauge
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