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Gauge blocks (also known as gage blocks, Johansson gauges, slip gauges, or Jo blocks) are a system for producing precision lengths. The individual gauge block is a metal or ceramic block that has been precision ground and lapped to a specific thickness. Gauge blocks come in sets of blocks with a range of standard lengths. In use, the blocks are stacked to make up a desired length (or height). Gauge blocks were invented in 1896 by Swedish machinist Carl Edvard Johansson. They are used as a reference for the calibration of measuring equipment used in
machine shop A machine shop or engineering workshop is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tool (machining), cutting tools to make parts, usua ...
s, such as micrometers, sine bars,
calipers Calipers or callipers are an instrument used to measure the linear dimensions of an object or hole; namely, the length, width, thickness, diameter or depth of an object or hole. The word "caliper" comes from a corrupt form of caliber. Many ty ...
, and dial indicators (when used in an inspection role). Gauge blocks are the main means of length standardization used by industry. An important feature of gauge blocks is that they can be joined together with very little dimensional uncertainty. The blocks are joined by a sliding process called , which causes their ultra-flat surfaces to cling together. A small number of gauge blocks can be used to create accurate lengths within a wide range. By using three blocks at a time taken from a set of 30 blocks, one may create any of the 1000 lengths from 3.000 to 3.999 mm in 0.001 mm steps (or .3000 to .3999 inches in 0.0001 inch steps).


Description

A gauge block is a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart. Standard grade blocks are made of a hardened steel alloy, while calibration grade blocks are often made of
tungsten carbide Tungsten carbide (chemical formula: ) is a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in in ...
(WC), chromium carbide (CrC) or
ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
( SiO2-based) because they are harder and wear less. Gauge blocks come in sets of blocks of various lengths, along with additional wear blocks, to allow a wide variety of standard lengths to be made up by stacking them. The length of each block is actually slightly shorter than the nominal length stamped on it, because the stamped length includes the length of one ''wring film'', a film of lubricant which separates adjacent block faces in normal use. The thickness of the wring film is about . The gauge's nominal length is also known as the '' interferometric length''. In use, the blocks are removed from the set, cleaned of their protective coating (
petroleum jelly Petroleum jelly, petrolatum (), white petrolatum, soft paraffin, or multi-hydrocarbon, CAS number 8009-03-8, is a semi-solid mixture of hydrocarbons (with carbon numbers mainly higher than 25), originally promoted as a topical ointment for i ...
or oil) and ''wrung together'' to form a stack of the required dimension. Gauge blocks are
calibrated In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...
to be accurate at and should be kept at this temperature when taking measurements. This mitigates the effects of
thermal expansion Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...
. The wear blocks, made of a harder substance like
tungsten carbide Tungsten carbide (chemical formula: ) is a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in in ...
, are included at each end of the stack, whenever possible, to protect the gauge blocks from being damaged in use. Machinists and toolmakers try to use a stack with the fewest blocks to avoid accumulation of size errors. For example, a stack totaling .638 that is composed of two blocks (a .500 block wrung to a .138 block) is preferable to a stack also totaling .638 that is composed of four blocks (such as a .200, .149, .151, and .138 all wrung together). As detailed in the
Grades Grade most commonly refers to: * Grading in education, a measurement of a student's performance by educational assessment (e.g. A, pass, etc.) * A designation for students, classes and curricula indicating the number of the year a student has reach ...
section, each block has a size tolerance of a few millionths of an inch, so stacking them together introduces a cumulative uncertainty. However, the stacked error from even multiple blocks is usually negligible in all but the most demanding uses. In a busy shop, some of the blocks will be in use elsewhere, so one creates a stack from the blocks available at the time. Typically the few millionths of an inch difference will not be detectable, or matter, in the context. Contexts demanding ultimate precision are rarer and require additional expense (for example, more sets of blocks and higher grades of blocks).


Wringing

''Wringing'' is the process of sliding two blocks together so that their faces bond. Because of their ultraflat surfaces, when wrung, gauge blocks adhere to each other tightly. Properly wrung blocks may withstand a pull. The mechanism is a combination of: *
Vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...
applies pressure between the blocks because the air is squeezed out of the joint *
Surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...
from oil and
water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...
that is present between the blocks *
Molecular attraction An intermolecular force (IMF; also secondary force) is the force that mediates interaction between molecules, including the electromagnetic forces of attraction or repulsion which act between atoms and other types of neighbouring particles (e.g. ...
that occurs when two very flat surfaces are brought into contact; this force causes gauge blocks to adhere even without surface lubricants, and in a vacuum It is believed that the last two sources are the most significant. Experiments with friction of the blocks suggest also that the removal of the oxide film from the steel surface by wringing plays an important role in the wringing action. There is no
magnetism Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, ...
involved, although to a user the clinging together of the blocks feels a bit like weak refrigerator magnets sticking together. Unlike magnets, however, the cling only lasts while the blocks are completely joined—the blocks do not attract each other across any visible gap, as magnets would. The process of wringing involves four steps: #Wiping a clean gauge block across an oiled pad. #Wiping any extra oil off the gauge block using a dry pad. #The block is then slid perpendicularly across the other block while applying moderate pressure until they form a
cruciform A cruciform is a physical manifestation resembling a common cross or Christian cross. These include architectural shapes, biology, art, and design. Cruciform architectural plan Christian churches are commonly described as having a cruciform ...
. #Finally, the block is rotated until it is inline with the other block. After use, the blocks are re-oiled or greased to protect against
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
. The ability of a given gauge block to wring is called '; it is officially defined as "the ability of two surfaces to adhere tightly to each other in the absence of external means." The minimum conditions for wringability are a
surface finish Surface finish, also known as surface texture or surface topography, is the nature of a interface (matter), surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a ...
of AA or better, and a flatness of at least . There is a formal test to measure wringability. First, the block is prepared for wringing using the standard process. The block is then slid across a reference grade ( flatness) quartz
optical flat An optical flat is an Optics, optical-grade piece of glass lapping, lapped and polishing, polished to be extremely flat on one or both sides, usually within a few tens of nanometres (billionths of a metre). They are used with a monochromatic li ...
while applying moderate pressure. Then, the bottom of the gauge block is observed (through the optical flat) for oil or color. For Federal Grades 0.5, 1, and 2 and ISO grades K, 00, and 0 no oil or color should be visible under the gauge block. For Federal Grade 3 and ISO grades 1 and 2, no more than 20% of the surface area should show oil or color. This test is hard to perform on gauge blocks thinner than because they tend not to be flat in the relaxed state.


Accessories

The pictured accessories provide a set of holders and tools to extend the usefulness of the gauge block set. They provide a means of securely clamping large ''stacks'' together, along with reference points, scribers, and various shapes of blocks that act like caliper jaws, either external or internal. Conical-tip ones ease measurement of center-to-center distances between hole centers. A stack of gauge blocks with external caliper-jaw accessories, all clamped together, acts as a quickly assembled custom-size go or no-go gauge. A special ''gauge block stone'' that cannot damage the surface is used to remove nicks and burrs to maintain wringability. There are two ''wringing pads'' used to prepare a gauge block for wringing. The first is an ''oil pad'', which applies a light layer of oil to the block. The second is a ''dry pad'', which removes any excess oil from the block after the oil pad has been used.


Grades

Gauge blocks are available in various grades, depending on their intended use. The grading criterion is tightness of tolerance on their sizes; thus higher grades are made to tighter tolerances and have higher
accuracy and precision Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value''. ''Precision'' is how close the measurements are to each other. The ...
. Various grading standards include: JIS B 7506-1997 (Japan)/DIN 861-1980 (Germany), ASME (US), BS 4311: Part 1: 1993 (UK). Tolerances will vary within the same grade as the thickness of the material increases. * reference (AAA): small tolerance (±0.05 μm) used to establish standards * calibration (AA): (tolerance +0.10 μm to −0.05 μm) used to calibrate inspection blocks and very high precision gauging * inspection (A): (tolerance +0.15 μm to −0.05 μm) used as
toolroom Tool and die makers are highly skilled crafters working in the manufacturing industries. Tool and die makers work primarily in toolroom environments—sometimes literally in one room but more often in an environment with flexible, semipermeable ...
standards for setting other gauging tools * workshop (B): large tolerance (tolerance +0.25 μm to −0.15 μm) used as shop standards for precision measurement More recent grade designations include (U.S. Federal Specification GGG-G-15C): * 0.5 – generally equivalent to grade AAA * 1 – generally equivalent to grade AA * 2 – generally equivalent to grade A+ * 3 – compromise grade between A and B and ANSI/ASME B89.1.9M, which defines both absolute deviations from nominal dimensions and parallelism limits as criteria for grade determination. Generally, grades are equivalent to former U.S. Federal grades as follows: * 00 – generally equivalent to grade 1 (most exacting flatness and accuracy requirements) * 0 – generally equivalent to grade 2 * AS-1 – generally equivalent to grade 3 (reportedly stands for American Standard - 1) * AS-2 – generally less accurate than grade 3 * K – generally equivalent to grade 00 flatness (parallelism) with grade AS-1 accuracy The ANSI/ASME standard follows a similar philosophy as set forth in ISO 3650. See the NIST reference below for more detailed information on tolerances for each grade and block size. Also consult page E-4 of
Commercial Gauge Block Tolerances
(Length refers to the calibrated thickness)


Manufacture

Gauge blocks are usually made either from hardened alloy
tool steel Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive ...
s,
ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
s or
cemented carbide Cemented carbides are a class of hard materials used extensively for cutting tool material, cutting tools, as well as in other industrial applications. It consists of fine particles of carbide cemented into a composite material, composite by a ...
s (such as
tungsten carbide Tungsten carbide (chemical formula: ) is a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in in ...
or tantalum carbide). Often the
carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of th ...
has a hardness of 1500
Vickers hardness The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness ...
. Long series blocks are made from high-quality steel having cross section (35 × 9 mm) with holes for clamping two slips together. These are also available in carbon steel material. Steel blocks are hardened and tempered. The
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...
is important because it slows down the gauge's rate of
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...
during use (this is why other kinds of gauges, such as pins, thread plugs, and rings, are also hardened.) The cutting of the blocks to size is accomplished with grinding followed by
lapping Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. Lapping often follows other subtractive processes with more aggressive material removal as a first ste ...
. Usually no plating or other coating is involved. Blocks are kept very lightly oiled, and are stored and used in dry climate-controlled conditions; unplated, uncoated steel gauge blocks can last for decades without rusting.


History

The gauge block set, also known as "Jo Blocks", was developed by the Swedish inventor Carl Edvard Johansson. Johansson was employed in 1888 as an armourer inspector by the state arsenal Carl Gustafs stads Gevärsfaktori (Rifle Factory of Carl Gustaf's town) in the town of
Eskilstuna Eskilstuna () is a Urban areas in Sweden, city and the seat of Eskilstuna Municipality, Södermanland County, Sweden. The city of Eskilstuna had 69,948 inhabitants in 2020, with a total population of 107,806 inhabitants in Eskilstuna municipality ...
, Sweden. He was concerned with the expensive tools for measuring parts for the Remington rifles then in production under licence at Carl Gustaf. When Sweden adopted a tailored variant of the Mauser carbine in 1894, Johansson was very excited about the chance to study Mauser's methods of measuring, in preparation for production under license at Carl Gustaf (which began several years later). However, a visit to the Mauser factory in Oberndorf am Neckar, Germany, turned out to be a disappointment. On the train home, he thought about the problem, and he came up with the idea of a set of blocks that could be combined to make up any measure. There had already been a long history of increasing use of gauges up to this time, such as gauges for filing and
go/no go gauge A go/no-go gauge is an inspection tool used to check a workpiece against its allowed tolerances via a go/no-go test. Its name is derived from two tests: the check involves the workpiece having to pass one test (''go'') and fail the other (''no- ...
s, which were custom-made individually in a toolroom for use on the shop floor; but there had never been super-precision gauge blocks that could be wrung together to make up different lengths, as Johansson now envisioned. Back home, Johansson converted his wife's Singer sewing machine to a grinding and lapping machine. He preferred to carry out this precision work at home, as the grinding machines at the rifle factory were not good enough. His wife, Margareta, helped him with the initial prototyping. Once Johansson had demonstrated his set at Carl Gustaf, his employer provided time and resources for him to develop the idea. Johansson was granted his first Swedish patent on 2 May 1901, SE patent No. 17017, called "Gauge Block Sets for Precision Measurement". Johansson formed the Swedish company CE Johansson AB (also known as 'CEJ') on 16 March 1917. Johansson spent many years in America; during his life he crossed the Atlantic 22 times. The first CEJ gauge block set in America was sold to Henry M. Leland at the Cadillac Automobile Company around 1908. The first manufacturing plant in America for his gauge block sets was established in Poughkeepsie, Dutchess County, New York, in 1919. The economic environment of the
post–World War I recession The post–World War I recession was an economic recession that hit much of the world in the aftermath of World War I. In many nations, especially in North America, economic growth continued and even accelerated during World War I as nations mo ...
and
depression of 1920–21 Depression may refer to: Mental health * Depression (mood), a state of low mood and aversion to activity * Mood disorders characterized by depression are commonly referred to as simply ''depression'', including: ** Major depressive disorder, al ...
did not turn out so well for the company, so in 1923 he wrote a letter to
Henry Ford Henry Ford (July 30, 1863 – April 7, 1947) was an American Technological and industrial history of the United States, industrialist and business magnate. As the founder of the Ford Motor Company, he is credited as a pioneer in making automob ...
of the
Ford Motor Company Ford Motor Company (commonly known as Ford) is an American multinational corporation, multinational automobile manufacturer headquartered in Dearborn, Michigan, United States. It was founded by Henry Ford and incorporated on June 16, 1903. T ...
, where he proposed a cooperation in order to save his company. Henry Ford became interested, and on 18 November 1923 he began working for Henry Ford in
Dearborn, Michigan Dearborn is a city in Wayne County, Michigan, Wayne County in the U.S. state of Michigan. An inner-ring Metro Detroit, suburb of Detroit, Dearborn borders Detroit to the south and west, roughly west of downtown Detroit. In the 2020 United States ...
. Hounshell (1984), citing Althin (1948) and various archive primary sources, says, "Henry Ford purchased the famous gaugemaking operation of the Swede C. E. Johansson in 1923 and soon moved it into the laboratory facility in Dearborn. Between 1923 and 1927, the Johansson division supplied 'Jo-blocks' to the Ford
toolroom Tool and die makers are highly skilled crafters working in the manufacturing industries. Tool and die makers work primarily in toolroom environments—sometimes literally in one room but more often in an environment with flexible, semipermeable ...
and any manufacturer who could afford them. It also made some of the Ford 'go' and 'no-go' gauges used in production as well as other precision production devices.". In the early 20th century, the U.S.
inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...
was effectively defined as 25.4000508 mm (with a reference temperature of ) and the U.K. inch at 25.399977 mm (with a reference temperature of ). When Johansson started manufacturing gauge blocks in inch sizes in 1912, Johansson's compromise was to manufacture gauge blocks with a nominal size of 25.4mm, with a reference temperature of , accurate to within a few parts per million of both official definitions. Because Johansson's blocks were so popular, his blocks became the ''de facto'' standard for manufacturers internationally, with other manufacturers of gauge blocks following Johansson's definition by producing blocks designed to be equivalent to his. In 1930, the
British Standards Institution The British Standards Institution (BSI) is the Standards organization, national standards body of the United Kingdom. BSI produces technical standards on a wide range of products and services and also supplies standards certification services ...
adopted an inch of exactly 25.4 mm. The
American Standards Association The American National Standards Institute (ANSI ) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organiz ...
followed suit in 1933. By 1935, industry in 16 countries had adopted the "industrial inch" as it came to be known, effectively endorsing Johansson's pragmatic choice of conversion ratio. In 1936, at the age of 72, Johansson felt it was time to retire and go back to Sweden. He was awarded the large gold medal of the
Royal Swedish Academy of Engineering Sciences The Royal Swedish Academy of Engineering Sciences (, IVA), founded on 24 October 1919 by King Gustaf V, is one of the royal academies in Sweden. The academy is an independent organisation, which promotes contact and exchange between business, ...
in 1943, shortly after his death. In 1948
Brown & Sharpe Brown & Sharpe is a division of Hexagon AB, a Sweden, Swedish multinational corporation focused mainly on metrology, metrological tools and technology. During the 19th and 20th centuries, Brown & Sharpe was one of the best-known and most influentia ...
bought the rights to the C.E. Johansson brand from Ford Motor Co., and blocks co-branded with the C.E. Johansson and
Brown & Sharpe Brown & Sharpe is a division of Hexagon AB, a Sweden, Swedish multinational corporation focused mainly on metrology, metrological tools and technology. During the 19th and 20th centuries, Brown & Sharpe was one of the best-known and most influentia ...
logos were made. Blocks co-branded with the C.E. Johansson and Ford logos are also sometimes still seen in use today.


Gauge pins

Similar to gauge blocks, these are precision-ground cylindrical bars, for use as plug gauges to measure hole diameters, or as parts of
go/no go gauge A go/no-go gauge is an inspection tool used to check a workpiece against its allowed tolerances via a go/no-go test. Its name is derived from two tests: the check involves the workpiece having to pass one test (''go'') and fail the other (''no- ...
s or similar applications.


Gauge rollers and balls

These are supplied as sets of individual rollers or balls as used in roller or ball bearings or tool and die making applications. Calibration balls can be used to calibrate contact angle goniometers, CNC machines and similar equipment.


See also

* * *


Notes


References

* . * * * .


Further reading

* * *


External links


The Joy of High TechThe Gauge Block Handbook; US National Institute of Standards & Technology (NIST) Monograph 180 with Corrections; 2004
{{DEFAULTSORT:Gauge Block Length, distance, or range measuring devices Metalworking measuring instruments Swedish inventions