DIGITAL MICROMETERS & OUTSIDE MICROMETERS
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PRODUCTS
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PRODUCTS
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PRODUCTS
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The micrometer is a measuring device for the unit of length.
The micrometer is universally recognised as a symbol of precision & accuracy – hence the reason Miller’s Tooling logo is based upon the actual micrometer reflecting our ethos.
Outside micrometer, inside micrometer, and depth micrometers are some
of the spinoffs of the actual micrometer head.
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An outside micrometer sometimes known as a micrometer screw gauge, is a device
incorporating a calibrated screw widely used for precise measurement of
components in mechanical engineering and machining as well as
most mechanical trades, along with other metrological instruments
such as dial, vernier, and digital calipers.
Micrometers are usually, but not always, in the form of calipers (opposing
ends joined by a frame), which is why micrometer
caliper is another common name. The spindle is a very accurately
machined screw and the object to be measured is placed between the spindle and
the anvil. The anvils are mostly carbide tipped, to resist wear & chips. The
spindle is moved by turning the ratchet knob or thimble until the object to be
measured is lightly touched by both the spindle and the anvil. “Feel” is a term
of actual feeling the faces touching at the correct pressure by the tradesman
to gain an accurate reading of the micrometer.
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Micrometers are also used in telescopes or microscopes to measure the apparent diameter of celestial bodies or microscopic objects. The micrometer used with a telescope was invented about 1638 by William Gascoigne, an English astronomer.
Colloquially the word micrometer is often shortened to mike or mic.
Micrometer stands are inexpensive & free
up both hands for accurate measurement
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History of the MICROMETER
The word micrometer is a neoclassical coinage from Greek micros, meaning "small", and metron, meaning "measure". The Merriam-Webster Collegiate Dictionary[2] says that English got it from French and that its first known appearance in English writing was in 1670. Neither the metre nor the micrometre (µm) nor the micrometer (device) as we know them today existed at that time. However, the people of that time did have much need for, and interest in, the ability to measure small things and small differences. The word was no doubt coined in reference to this endeavor, even if it did not refer specifically to its present-day senses.
The first ever micrometric screw was invented by William Gascoigne in the 17th century, as an enhancement of the vernier; it was used in a telescope to measure angular distances between stars and the relative sizes of celestial objects.
Henry Maudslay built a bench micrometer in the early 19th century that was jocularly nicknamed "the Lord Chancellor" among his staff because it was the final judge on measurement accuracy and precision in the firm's work. In 1844 details of Whitworth's
Gascoigne's Micrometer as drawn by Robert Hooke
Workshop micrometer were published. This was described as having a strong frame of cast iron, the opposite ends of which were two highly finished steel cylinders, which traversed longitudinally by action of screws. The ends of the cylinders where they met was of hemispherical shape. One screw was fitted with a wheel graduated to measure to the ten thousandth of an inch. His object was to furnish ordinary mechanics with an instrument which, while it afforded very accurate indications, was yet not very liable to be deranged by the rough handling of the workshop.
The first documented development of handheld micrometer-screw calipers was by Jean Laurent Palmer of Paris in 1848; the device is therefore often called palmer in French, and tornillo de Palmer ("Palmer screw") in Spanish. (Those languages also use the micrometer cognates: micromètre, micrómetro.) The micrometer caliper was introduced to the mass market in anglophone countries by Brown & Sharpe in 1867, allowing the penetration of the instrument's use into the average machine shop. Brown & Sharpe were inspired by several earlier devices, one of them being Palmer's design. In 1888 Edward W. Morley added to the precision of micrometric measurements and proved their accuracy in a complex series of experiments.
The culture of toolroom accuracy and precision, which started with interchangeability pioneers including Gribeauval, Tousard, North, Hall, Whitney, and Colt, and continued through leaders such as Maudslay, Palmer, Whitworth, Brown, Sharpe, Pratt, Whitney, Leland, and others, grew during the Machine Age to become an important part of combining applied science with technology. Beginning in the early 20th century, one could no longer truly master tool and die making, machine tool building, or engineering without some knowledge of the science of metrology, as well as the sciences of chemistry and physics (for metallurgy, kinematics/dynamics, and quality).
Micrometers come in many forms, the basic outside micrometer ranges 0 – 25mm ( or imperial equiv.)
Micrometers step up in 25mm increments ie; 0 -25mm then 25 – 50mm, 50 – 75mm etc. Universal micrometers or interchangeable micrometer sets are also popular to cover large diameter ranges. The anvils can vary on micrometer to create blade micrometer, disc brake micrometer, tube micrometer, thread micrometer, V anvil micrometer, can seam micrometer, bore micrometer, ball micrometer, bench micrometer, limit micrometer, stop micrometer & many more, all suit a specific job.
Operating principles of a micrometer
Animation of a micrometer used to measure an object (black) of length = 4.14 mm
Micrometers use the principle of a screw to amplify small distances[6] (that are too small to measure directly) into large rotations of the screw that are big enough to read from a scale. The accuracy of a micrometer derives from the accuracy of the thread-forms that are at its heart. In some cases it is a differential screw. The basic operating principles of a micrometer are as follows:
- The amount of rotation of an accurately made screw can be directly and precisely correlated to a certain amount of axial movement (and vice versa), through the constant known as the screw's lead . A screw's lead is the distance it moves forward axially with one complete turn (360°). (In most threads [that is, in all single-start threads], lead and pitch refer to essentially the same concept.)
- With an appropriate lead and major diameter of the screw, a given amount of axial movement will be amplified in the resulting circumferential movement.
For example, if the lead of a screw is 1 mm, but the major diameter (here, outer diameter) is 10 mm, then the circumference of the screw is 10π, or about 31.4 mm. Therefore, an axial movement of 1 mm is amplified (magnified) to a circumferential movement of 31.4 mm. This amplification allows a small difference in the sizes of two similar measured objects to correlate to a larger difference in the position of a micrometer's thimble. In some micrometers, even greater accuracy is obtained by using a differential screw adjuster to move the thimble in much smaller increments than a single thread would allow.[7][8][9]
In classic-style analog micrometers, the position of the thimble is read directly from scale markings on the thimble and shaft. A vernier scale is often included, which allows the position to be read to a fraction of the smallest scale mark. In digital micrometers, an electronic readout displays the length digitally on an LCD display on the instrument. There also exist mechanical-digit versions, like the style of car odometers where the numbers "roll over".
Imperial system
Micrometer thimble showing 0.276 inch
The spindle of a micrometer graduated for the Imperial and US customary measurement systems has 40 threads per inch, so that one turn moves the spindle axially 0.025 inch (1 ÷ 40 = 0.025), equal to the distance between two graduations on the frame. The 25 graduations on the thimble allow the 0.025 inch to be further divided, so that turning the thimble through one division moves the spindle axially 0.001 inch (0.025 ÷ 25 = 0.001). Thus, the reading is given by the number of whole divisions that are visible on the scale of the frame, multiplied by 25 (the number of thousandths of an inch that each division represents), plus the number of that division on the thimble which coincides with the axial zero line on the frame. The result will be the diameter expressed in thousandths of an inch. As the numbers 1, 2, 3, etc., appear below every fourth sub-division on the frame, indicating hundreds of thousandths, the reading can easily be taken.
Suppose the thimble were screwed out so that graduation 2, and three additional sub-divisions, were visible (as shown in the image), and that graduation 1 on the thimble coincided with the axial line on the frame. The reading would then be 0.2000 + 0.075 + 0.001, or .276 inch.
Metric system
Micrometer thimble reading 5.78mm
The spindle of an ordinary metric micrometer has 2 threads per millimetre, and thus one complete revolution moves the spindle through a distance of 0.5 millimeter. The longitudinal line on the frame is graduated with 1 millimetre divisions and 0.5 millimetre subdivisions. The thimble has 50 graduations, each being 0.01 millimetre (one-hundredth of a millimetre). Thus, the reading is given by the number of millimetre divisions visible on the scale of the sleeve plus the particular division on the thimble which coincides with the axial line on the sleeve.
Suppose that the thimble were screwed out so that graduation 5, and one additional 0.5 subdivision were visible (as shown in the image), and that graduation 28 on the thimble coincided with the axial line on the sleeve. The reading then would be 5.00 + 0.5 + 0.28 = 5.78 mm.
Vernier scale on micrometer
Micrometer sleeve (with vernier) reading 5.783mm
Some micrometers are provided with a vernier scale on the sleeve in addition to the regular graduations. These permit measurements within 0.001 millimetre to be made on metric micrometers, or 0.0001 inches on inch-system micrometers.
The additional digit of these micrometers is obtained by finding the line on the sleeve vernier scale which exactly coincides with one on the thimble. The number of this coinciding vernier line represents the additional digit.
Thus, the reading for metric micrometers of this type is the number of whole millimetres (if any) and the number of hundredths of a millimetre, as with an ordinary micrometer, and the number of thousandths of a millimetre given by the coinciding vernier line on the sleeve vernier scale.
For example, a measurement of 5.783 millimetres would be obtained by reading 5.5 millimetres on the sleeve, and then adding 0.28 millimetre as determined by the thimble. The vernier would then be used to read the 0.003 (as shown in the image).
Inch micrometers are read in a similar fashion.
Note: 0.01 millimetre = 0.000393 inch, and 0.002 millimetre = 0.000078 inch (78 millionths) or alternatively, 0.0001 inch = 0.00254 millimetres. Therefore, metric micrometers provide smaller measuring increments than comparable inch unit micrometers—the smallest graduation of an ordinary inch reading micrometer is 0.001 inch; the vernier type has graduations down to 0.0001 inch (0.00254 mm). When using either a metric or inch micrometer, without a vernier, smaller readings than those graduated may of course be obtained by visual interpolation between graduations.
