The micrometers —Also called Palmer gauges or Palmer screws— are used in different industries: metalworking, plastics, bolting, automotive, and so on. Is a Measuring instrument that allows to measure lengths with an accuracy of up to one thousandth of a millimeter.
As with the Vernier caliper or caliper, there are different types of micrometer, either to measure the outside, the inside, heights, depths, and so on. They are also divided into analog and digital. We will see below the different types – according to this last criterion – and the correct way to operate them.
Analog and digital micrometers
There are basically two types of micrometer available on the market: analog and digital, and each of these types is available for the different micrometer models depending on the measurement to be carried out: external and internal parallels, external and internal cylinders, special cylindrical parts – such as wicks, strawberries, and chalicears — plus height and depth measurements.
Mechanical or analog micrometers
Are the micrometers More traditional and preferred by many professionals and technicians, since machine reading, for someone experienced, is much simpler and more reliable compared to digital ones, and the use of batteries is not required for it. On the other hand, some novice operators may have difficulties at first, since the reading is not immediate and requires some practice to do it fluently.
This type of micrometer —when they work in the metric system— has a screw inside it with a pitch of half a millimeter. Thus, a full turn of the drum will cause the stop plates to separate exactly half a millimeter. Using this principle, it is possible to achieve a resolution of up to one thousandth of a millimeter (0.001 mm), although not all micrometers they have the necessary vernier; in these cases its nominal precision is one hundredth of a millimeter (0.01 mm).
There are different models of micrometer, according to their use: from those for general use to the highly specific ones (such as the micrometer depth measurement gauge, seen below). However, the principle of operation is similar: they all have a screw, an approach drum and a cricket to achieve the support of the stop plates.
Depth micrometer. The coliza can be seen above the instrument.
It is important, when working with this type of micrometer, to take special care not to force the drum, and to bring the stops closer by making exclusive use of the cricket or ratchet. This device is prepared to adjust the stops against the piece to be measured with the necessary pressure; once secured, the mechanism falsely rotates the ratchet or cricket — hence its name — and prevents damage to surfaces or the instrument.
There are some micrometers equipped with a dial with a needle, which indicates the measurement in a perhaps more direct way to the operator, although the vast majority of the time these micrometers they are limited to a precision of one hundredth. Furthermore, due to the complexity of the mechanism necessary to move the needles, these instruments are somewhat cumbersome, making their use only practical in laboratory or technical office environments.
Three-contact micrometer, especially for measuring cylindrical parts, including strawberries, wicks, drills and chalicears.
In this case, the operating principle is similar to its analog pairs, although an encoder is used as an interface for the measurement, with which the measurement appears easily readable on a digital display. The reading, thus, is much easier than in its analog equivalents, although at the cost of sacrificing reliability, since if the instrument is powered by faulty batteries, a false measurement can occur.
A great advantage over analog micrometers is that, due to their digital nature, they allow measurements to be instantly converted to inches and arbitrarily set to zero on the measurement.
Inside of a micrometer or Palmer caliper
Whether analog or digital, outdoor or indoor, height or depth, the interior of the micrometers outdoors does not change much. The micrometer screw is generally manufactured with a length of 25 mm, with which each instrument will be able to carry out measurements within that range, starting, of course, from a measurement zero arbitrary; this is standardized in steps of 25 mm: from 0 to 25 mm, from 25 mm to 50 mm, from 50 mm to 75 mm, and so on.
So, according to the application or the work to be done, it is the type of micrometer that you should buy. Also, according to the use that the micrometer, the body or arch is modified, making it larger or replacing it with a base, a tripod, etc. Most of the micrometers of general use have an insulating insert that allows taking it without affecting, with the body heat, the measurement by means of the expansion of said arc.
Micrometer with stop plates for threads.
The stop plates are generally interchangeable; This is because, with use, the ground and cemented surface of these plates tends to wear out.}
In some specific measurement models – such as the micrometers for threads, gears, or grooves — these stops will need to be replaced to match their geometry with the thread type, groove size, or gear modulus to be measured.
Special micrometer for measuring grooves. Note the sharp wedge-shaped stop plates, and the part used to calibrate the instrument.
When the stop plates are changed, it is necessary to verify that the instrument is correctly calibrated. For this they are usually accompanied by small calibration pieces like the one that can be seen in the photograph above.
Tips for use: micrometer
- Never adjust the stops against the workpiece using the drum; This should only be used to bring the plates closer together and the operation should be completed using the cricket or ratchet.
- The instrument should be held only by the thermal insulation plates (usually black) that are on the body. It should never be taken directly from the tip, as body heat will expand the metal, thus modifying the distance and measurement.
- Do not separate the piece from between the stops without first separating them unless the surface is perfectly parallel and mirror polished; otherwise you could scratch the plates or force them, thus losing the calibration of the instrument.
- Save the micrometers in their respective cases. Do not expose them to direct heat, excessive humidity, or corrosive environments or suspended particles.
- If possible, clean the instrument regularly using a cotton cloth and a neutral cleaning agent. Prevent the product from entering the mechanism.