Quick Guide to Precision Measuring Instruments

PG13Quick Guide to MeasurementGuidelines for Self-made FixturesA micrometer head should be mounted by the stem in an accurately machined hole using a clamping method that does not exert excessive force on the stem. There are three common mounting methods as shown below. Method 3 is not recommended. Adopt methods (1) or (2) wherever possible.(Unit: mm)Graduation Styles●Care is needed when taking a reading from a mechanical micrometer head, especially if the user is unfamiliar with the model.●The "normal graduation" style, identical to that of an outsidemicrometer, is the standard. For this style the reading increases as the spindle retracts into the body.●On the contrary, in the “reverse graduation” style the reading increases as the spindle advances out of the body.●The "bidirectional graduation" style is intended to facilitate measurement in either direction by using black numerals for normal, and red numerals for reverse, operation.●Micrometer heads with a mechanical or electronic digital display, which allow direct reading of a measurement value, are also available. These types are free from misreading errors. A further advantage is that the electronic digital display type can enable computer-based storage and statistical processing of measurement data.Thimble Diameter●The diameter of a thimble greatly affects its usability and the "fineness" of positioning. A small-diameter thimble allows quick positioning whereas a large-diameter thimble allows fine positioning and easy reading of the graduations. Some models combine the advantages of both features by mounting a coarse-feed thimble (speeder) on the large-diameter thimble.Normal graduation styleReversegraduation styleBidirectional graduation style 05045502025455009080102020801090502025Mounting methodPoints to keep in mind(1) Clamp nut (2) Split-body clamp(3) Setscrew clamp Stem diameterø9.5ø10ø12ø18ø9.5ø10ø12ø18ø9.5ø10ø12ø18Mounting holeFitting toleranceG7+0.005 to +0.020G7+0.006 to +0.024G7+0.005 to +0.020G7+0.006 to +0.024H50 to +0.006H50 to +0.008PrecautionsCare should be taken to make Face A square to the mounting hole.The stem can be clamped without any problem at squareness within 0.16/6.5.Remove burrs generated on the wall of the mounting hole by the slitting operation.M3x0.5 or M4x0.7 is an appropriate size for the setscrew.Use a brass plug under setscrew (if thickness of xture allows) to avoid damaging stem. Face A

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