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IntroductionMeasuring tools for small engines are divided into three categories.Direct readingMeasurement transferringReject gages
Direct Reading Measuring ToolsSmall engines use two types of direct reading measuring tools:MicrometersCalipers
Micrometer IntroductionA micrometer is a mechanical device designed to measure distances as small as 1/10,000 of an inch (0.0001 in).Micrometers are only one (1) inch long.The micrometer is used with different types and sizes of frames to provide precise measurements of many different objects.Small engines uses three (3) types of micrometers:Micrometer caliperInside micrometerDepth gauge micrometer
Micrometer calipers are available in mechanical and digital models.
Micrometer CaliperA micrometer caliper uses a frame that allows the micrometer to measure the thickness of objects.For small engine use, different frame sizes are used to provide a wider measurement range.One inchTwo inchEtc.
Reading Micrometer Caliper-partsThe first step in being able to read a micrometer is learning the names of the parts.The face of the anvil and the face of the spindle are the contact surfaces.The spindle and thimble turn together.The ratchet/friction stop improves the repeatability of measurements for beginners.A micrometer caliper is read at the point were the edge of the thimble crosses the barrel scaleInsure the lock is released before trying to turn the thimble..
Reading Micrometer Caliper-barrelA micrometer caliper is read just like an ruler.Start by determining the smallest whole unit, and then determine the values of each sub division. The smallest whole unit is determined by the frame size.One (1) inch frame = 0.0 smallest whole unitTwo (2) inch frame = 1.0 smallest whole unit.Etc.The micrometer barrel scale is one (1) inch long and is divided into ten (10) sections. Each number on the barrel scale = 1/10 or 0.1 inch.
Reading Micrometer Caliper-barrelEach 1/10 of an inch on the barrel scale is divided into 4 segments.Each short line = 0.25 inches (25 thousands of an inch).
Reading Micrometer Caliper-thimbleThe last step is reading the value on the thimble scale.The thimble scale subdivides the last segment on the barrel scale.The smallest segment on the barrel is 25 thousands (0.025).The thimble is divided into 25 segments = 1/1,000 or 0.001 inch.
Micrometer Caliper ExampleDetermine the reading for the micrometer caliper in the illustration.Smallest whole unit0.000Tenths of an inch0.300Twenty five thousands ( 0.025 x 2 )0.050Thousands0.015 Sum (measurement)0.365
Micrometer Caliper-digitalMost measuring tools are available with a digital readout.AdvantagesEasier to read.Can be interfaced with data collection devices for automatic recording.Easy to convert between English and metric units.DisadvantagesRequires batteryMore expensive
Inside MicrometerInside micrometers have been replaced by dial calipers and other tools for small gas engines.The principles for reading are the same.The primary difference is determining the smallest whole unit.The physical size of the micrometer limits the smallest whole unit to 1 or 1-1/2 inch.Extensions are added to set the minimum size to the desired range.
Inside Micrometer ExampleRead the inside micrometer in the illustration.Smallest whole unit1.500Tenths0.200Twenty Five Thousands0.025Thimble0.014 Sum (reading)1.734
Inside Micrometer Example 2Inside micrometers use extensions to change the range of measurements.Adding an extension increases the minimum measurement.Smallest whole unit2.000Tenths0.200Twenty five thousands0.075Thousands0.001 Reading2.276In this example a 1/2 inch extension has been added.Note: when the zero on the thimble is close to the reference line and a 25 thousands line is close to the edge of the thimble, it may be difficult to determine if the last line that should be counted. If the thimble zero is above the reference line the line is not counted. If it is below it should be counted.
Depth Gauge MicrometerDepth gauge micrometers are used to measure the depth of blind holes, slots, key ways, etc.The spindle length can be changed to set the micrometer for the desired range of measurement.To read a depth gauge micrometer you must visualize the distance that has been covered by the thimble.ThimbleSpindle
Depth Gauge Micrometer ExampleSmallest whole unit0.000Tenths0.800Twenty Five Thousands0.050Thousands0.017 Sum (reading)0.867Read the depth gauge micrometer in the illustration
IntroductionCalipers can be direct reading or measuring transferring tools.Direct reading calipers are capable of a wider measurement range than micrometer calipers.Six (6), eighteen (18) and twenty four (24) inch are popular.Three common designs of direct reading calipers;VernierDialDigital
Vernier CaliperVernier calipers are an old tool that has been mostly replaced by dial and digital calipers.They are manufactured with decimal scales, metric scales and fractional scales.The Vernier scale is still used on many mechanical measuring tools.
Vernier ScaleThe reference point is the 0 on the vernier scale.To read a Vernier, the line of coincidence must be located.The line of coincidence (LOC) is the line on the Vernier that coincides with a line on the main scale.Illustration LOC = 19In theory only one LOC is possible, but usually when reading the vernier it appears several exist. When this occurs pick the middle line.A Vernier is a mechanical means of magnifying the last segment on the main scale so addition subdivisions can be made.
Vernier Caliper-practiceSmallest whole unit1.000Tenths of an inch0.200Twenty five thousands 0.000Vernier scale0.011 Sum (measurement)1.211LOCRead the Vernier caliper in the illustration.
Dial CaliperA dial replaces the Vernier. This makes the caliper easier to read.The reader must still determine the units and graduations.
Measurement Transferring Tools
IntroductionMeasurement transferring tools are tools that collect a measurement, but do not have a scale to read the measurement.Common tools are:Spring calipersDividersTelescoping gaugesBall gauges
Spring CalipersSpring calipers are used to transfer measurements.Three types of spring calipersOutsideInsideHermaphrodite
DividersDividers are very useful for laying out several equal distances or transferring a distance measurement when other measuring devices cannot be used.
Telescoping gagesTelescoping gages are used to measure inside diameters.One or both ends are spring loaded so they can be retracted and inserted into the hole being measured.The measurement is made with a caliper or micrometer.
Ball GaugesBall gauges are use to transfer measurements that are too small for telescoping gauges.The ball is split and a tapered wedge is used to increase and decrease the diameter of the ball halves.