Measurement

Overview

Knowing how to measure accurately is an extremely important skill that all engineers should take the time to master. This information will help you learn some of the basics of measurement. If you are interested in learning more, please contact the machine shop staff.

Measuring Introduction Notes

Measuring Devices Overview
There is an extensive array of measuring tools in industry. This overview concentrates on what we have in our university shops.

English System v/s Metric System
We generally use the English measuring system in our shops. The majority of our tools use the English system. We can use the metric system if it is required.

How accurate do you need to be?
Accuracy of a project is determined by several factors:

Specified on the drawing – can be within .001”, .005”, or if no figure is given, it is assumed to be within .010”.
Indicated by the material used – plastics or Teflon are pliable enough to vary .020” whereas metals—aluminum and steels—can be cut with much greater accuracy.
Application – some projects simply do not require such a fine level of accuracy. You can expect to pay accordingly based on the level of accuracy specified.

Drill Classifications – Inch, Number, and Letter

Inch – 1/16th” to 1” by 64ths (Standard Set)
Number – Sizes from #1 to #80 (Sizes fall in between the Inch and Letter sizes)
Letter – Sizes from A to Z (Sizes fall in between the Inch and Number sizes)
Special – You can order any diameter drill or reamer you may need.

Rulers, Scales, and Measuring Tapes
Generally used for rough starting measurements like laying out material to be cut to size – for later turning or milling to its final dimensions.

Functions of a Caliper
Measures inside, outside, and depth dimensions of a part to an accuracy of .001”. A ‘Touch’ needs to be developed so that you do not over-tighten the caliper and interfere with the proper measurement.

Micrometer Types
In general micrometers are more accurate for small, sub 1” round parts. Micrometers feature a clutched tensioner knob that prevents over-tightening and provides more accurate measurements.

Outside – A separate tool is required for each size range (1” to 2”, 2” to 3”,etc.) as the tool only adjusts for the last inch of the given size range.
Inside – Like the outside style a separate tool is required for each range except the range is only about 0.1”.
Depth – Uses a single base micrometer with a 1” range and a set of standard length extensions for varying depths.
Machine – Lathe and Mill – Built-in micrometers for reading movement of the machines in the X, Y, and Z direction. Some backlash usually needs to be compensated for on older machines that do not use ball screws.

Hole Gauges - Expanded inside a bored hole (>0.5”) and is measured with a micrometer.

Telescoping Gauges – Uses opposing spring loaded probes for measuring larger holes. Once a satisfactory reading is taken and locked tool is measured with a micrometer.

Dial Indicators – Used to measure displacement on flat or round surfaces by means of the dial sweep. Some models indicate variations by digital readout.

Gage Blocks (Jo blocks) – Used for calibration and to setup tooling.

Sine Bar – Sets up or measures angles by means of trigonometry.

Measuring Threads
Machine threads are measured using thread gauges that utilize a range of combs matching the various thread pitches – one for English and one for metric. We also have sets of threaded gauges for English and metric.

English – Thread pitch is measured as threads per inch
Metric – Thread pitch is measured as distance between threads in mms

Thread Gauges - Utilize a range of combs matching the various thread pitches - English and metric. We also have sets of screw-in gauges for English and metric.

Radius Gauges – A flat set of precisely ground gauges for verifying interior and exterior radii. Range in size from 1/64” to ½”.

Digital Readouts (DRO) – LED device attached to a machine tool to accurately measure its position in the X, Y, and Z plain.