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Mechanical Micrometre Parts Explained

Mechanical Micrometre Parts Explained

Posted by Jonathan Gee, EMG Precision Ltd. on Oct 07, 2021

What are the parts of a micrometre?

An in-depth look at all the main components are are assembled in order to make a working mechanical vernier micrometre. We take a look at the relationship between the parts, how they work and what their function if. We also consider how certain parts contribute to the overall quality and performance of a micrometre.

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Diagram & Legend of all the components that are assembled together to make a micrometre.

Parts of a Mechanical Vernier Micrometre Explained...

Close up image of the scale markings on a micrometers Sleeve and Spindle.

What are the parts that make a Mechanical Micrometre?

Check out the various parts of a mechanical vernier micrometer below. We have broken the product down into its main parts and described what they do and how they interact with the rest of the assembly and the user. This article on a micrometers parts explained forms part of a series of posts that look to fully inform you of of all the elements related to the engineering measuring tool that is the micrometer.

For the sharper eyed of you, you may notice that we have spelt micrometre in a couple of different ways. Micrometre is the most commonly used iteration and is used by the International Bureau of Weights & Measures. Micrometer is the American spelling. Don't quote me on it, but I heard that they spelt it differently to revolt against the introduction of the metric system, but I might be mis-informed. Send us a message at info@emgprecision.com if you know the real reason.

A - Frame Body

What does the U-Shape Frame Body do on a mechanical micrometre?

The frame of a micrometre fundamentally revolves around a U-shape section. This shape is what determines the maximum allowable measuring distance. The design of this U-Shape can change depending on the style or even the size of the micrometre in question. The Frame (A) is designed to support both the Anvil (B) and the Spindle (D) and its connected assemblies, the Sleeve (F), Thimble (G) and Ratchet (H). You will often find a Spindle Lock (E) incorporated into the frame of the micrometer. It is not unusual for some micrometres to have a ribbed of triangular design. This is often the case to add structural rigidity. Some models offer thermally non-conductive plastic covers over the top of the U frames. This is to help preventing transferring heat from the user to the micrometer and potentially causing thermal movement. It can also provide ergonomic benefits for the user.

Micrometer Frame Examples...

As you can see from the example photographs below the design of micrometer u-shaped frames can vary significantly.

Large size solid steel frame micrometer.
Steel framed micrometer with holes cutout.
Tube fabricated micrometer to achieve large capacity and low weight.

B - Anvil

What is the anvil on a micrometre?

The Anvil is the fixed element of the mechanical micrometre that the component or stock item rests against ready for the item to be measured. The design of the anvil can often change depending on the intent of the objects is it designed to measure. Some examples could be Blade Anvils, Disc, Point or spherical designs to name but a few. Some models of micrometer are multi-functional and come with interchangeable anvils to allow for different measurement functions.

The quality of the anvil plays an important part in the overall accuracy of the micrometre and its useful life. The flatness accuracy of the anvil plays an important part for obvious reasons as well as the material of which it is made. Dasqua Anvils are made from a speciality carbide that is highly resistant to rusting but you must be careful with some models who only use a surface coating of carbide or a plain carbon steel as these will have a short, useful service life. We will discuss this in more detail under the title ‘Measuring Faces’.

Close up photo of the Anvil on a micrometer.

C - Measuring Faces

What are the measuring surfaces on micrometres made of and why are they important?

As briefly discussed above the Measuring Surfaces are critical to the performance of a micrometer. Often anvil flatness or measuring surface flatness specification will be quoted. This obviously has an impact on the overall accuracy and repeatability of any type of micrometer. It is generally considered that solid carbide measuring surfaces are preferable over hardened steel. A carbon steel anvil & measuring face can easily become spoiled by surface rust over time through simple oxidisation. Some cheaper micrometers offer a thing skim of carbide for the contact surfaces, The best micrometers feature a solid section of carbide that is ground and lapped like the offering from Dasqua. Their use of a speciality carbide is highly resistant to rust and damage, it holds an extremely accurate surface finish and flatness and will lead to an extended accurate service life. Surfaces that are looked after through the adoption of good manufacturing practise and careful use will likely last for years and years after the standard 24-month warranty on our solutions.

Extreme close up of the spindle and avil measuring faces of a mechanical vernier micrometer.

In this close up photo of the spindle and anvil you can see the incredibly accurate and flat finish on the anvil. You can also actually see the solid carbide sections that form the full, hard wearing contact points.

D - Spindle

What is the spindle on a micrometre and what does it do?

Like the anvil we discussed earlier and the same measuring surfaces it shares, the Spindle (D) functions like an anvil, only it is mobile. The spindle is connected by a screw to the Thimble (G). When the Thimble is turned by the user, the screw rotates the Anvil while at the same time axially moves forward and backwards depending on which way the Thimble is rotated. This functionality serves to tighten the moveable anvil against the object being measured and in turn against the opposing anvil. The spindle design can generally be considered as a threaded tube that connects to the Thimble. Just like the Anvil, the spindle has a designated contact surface element which is often a precision ground and lapped carbide.

Picture of an anvil and spindle on a micrometer.
Full photo of a Dasqua Micrometer on a white background photographed face on flat.
Close up photo of the stainless steel screw element inside a micrometer assembly.

E - Spindle Lock

What does the Spindle Lock do on a micrometre?

The spindle lock can be a very useful feature on a micrometer. Exactly as it sounds, the spindle lock, when engaged locks the spindle and prevents it from rotating. In other words, this locks in the position of the spindle and therefore the thimble against the sleeve, as all these elements are connected. This makes it easier to take manual readings without the risk of the spindle moving slightly whilst in your hands. It is not always necessary to use the spindle lock, but when the object you are measuring is awkward to position or hold, it can be beneficial to lock the spindle with your thumb, immediately after adjusting the thimble with your fingers on the same hand. The lock can be used to suspend objects in measurement mode to share readings with colleagues. With the use of a standard or professional micrometer stand, the spindle lock can be engaged more comfortably as the user does not have to concern themselves with supporting the micrometer itself. This can prove very helpful with large micrometers or heavy repetition.

F - Sleeve

What is the Sleeve for on a micrometer?

The sleeve is a barrel that is fixed permanently to the assembly, in so much as this component does not move axially forward or backwards and it does not rotate. The primary scale of the micrometer is most often marked on this component. Micrometers with a scale in metric or imperial are commonly available. For those not familiar with it, an imperial scale is one that is designed to measure in inches and fractions thereof. It is entirely typical for a index line to be marked or engraved on the Sleeve also.

G - Thimble

What is a Thimble on a micrometer and what does it do?

Just like the Sleeve (F), the Thimble (G) is a barrel shape that looks very similar to the sleeve. It really is much simpler than it sounds, but the Thimble acts like a sleeve, rotating around the sleeve that we previously mentioned. I told you it sounds silly. The Thimble is of a larger diameter than the sleeve and it rotates around the outer side of the sleeve. The thimble carries a second scale, that matches the unit of measurement type that the sleeve is etched with. The Thimbles scale is a subdivision of the primary scale on the sleeve. One division on the sleeve, is then broken down into multiple divisions on the Thimble to fine tune the accuracy readings.

H - Ratchet

What does the Ratchet do on a Micrometer?

Like the Thimble, the Ratchet is a rotatable cylinder that is connected directly to the spindle and contributes to the application of force on the component to be measured as it is sandwiched between the Anvil (B) and the Spindle (D) Measuring Faces (C). The ratchet is designed to be used the apply the final, and correct amount of pressure to the component to get a correct, and representative reading. The Ratchet is usually designed to provides subtle feedback through the user’s fingers and an audible click when the correct amount of pressure is applied to the component through the Spindle. The ratchet helps the user to not overtighten the pressure, and subsequently risk damaging your micrometre, and to indicate to the user that the right amount of force as been applied, this giving a trustworthy reading. We cover how to use a mechanical vernier micrometre if our article aptly named, “How to use a mechanical or manual micrometer?”.

I - Scales - Primary & Secondary Scales

What are the Scales for on a Vernier micrometer?

On a vernier micrometer, the scales are used to take the measurement. After tightening the spindle onto the component to be measure the user takes a reading off the scales to provide them with the measurement of the component inside the tolerance specification of that model. The Scales are normally available in Metric (mm) or Imperial (Inches) and are almost exclusively only available in one or the other. Typically the main scale, or primary scale is located on the Sleeve (F) and the secondary scale, or second scale is located on the Thimble (G). The divisions on these scales dictate the precision of the readings that can be taken. Some higher precision models have an tertiary scale, or third scale, often located on the sleeve which is used to provide another level of increased precision.

J - Screw

What does the Screw on a Micrometre Do?

Things get serious when we start talking about the screw inside a micrometre. This is really where all the action takes place and is what fundamentally defines the performance and precision of the micrometre. The screw is located centrally inside the Sleeve and Thimble assembly and is connected to the Spindle itself. You can see in the photo below how a typical micrometre screw looks like. The quality of the materials used and the processing techniques affect how smooth and accurate the micrometer is overall. Many cheap versions of micrometres use a basic carbon steel for the screw. This can cause many issues in the future with corrosion and surface oxidisation effecting the smoothness and accuracy of the unit. Dasqua Micrometres use a fully double ground, hardened stainless steel screw for maximum performance and longevity. The screw is the critical component that transfers rotation of the Thimble and Ratchet, into axial & linear motion of the Spindle.


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How to use a mechanical or manual micrometer?

Author Jonathan Gee / About Micrometers Series / Published: TBC