Precision Measuring Tools: Micrometers, Gauges, and Calibers

Depth Micrometer Features and Components

The depth micrometer ensures a precise measurement of the depth of hole flutes. It differs from standard micrometer measurements by replacing the arc with a flat base.

Key Parts of a Depth Micrometer

• Steel Bridge
• Support plane
• Mobile axis (Spindle)
• Locking device
• Graduated body (Sleeve)
• Graduated drum (Thimble)

This axis measures available variables that are interchangeable. To ensure the measurement is correct, it is essential that the plane of the micrometer bridge fits perfectly to the surface of the piece, maintaining the greatest possible contact.

Internal Micrometer for Large Hole Diameters

The internal micrometer is used to measure hole diameters and other dimensions greater than 50mm. It is formed by a micrometer head on which one or more interchangeable prolongation axes can be mounted.

Internal Micrometer Components

• Graduated drum (Thimble)
• Graduated body (Sleeve)
• Micrometer head
• Locking device
• Fixed point of the head
• Spherical tip
• Flat tip

The combined axes are contained within the prolongation tubes; when attached, they can create multiple combinations for various measurements.

Micrometer with Expandable Contact

For a micrometer with expandable contact, the measurement is made by three heads located at 120-degree intervals. These expand symmetrically when pushed by a threaded cone, which is fixed to the shaft and controlled by a button. They are most suitable for testing all kinds of holes, as the support of the three legs determines the level of reading.

Precision Steel Gauge Blocks

Gauges are prismatic blocks of special steel with two opposite sides levigated to be perfectly flat and parallel, forming the measurement surface. The thickness of the block is constant at any point on the surface; the nominal dimension is graduated on one of its faces. The manufacture of these steel blocks involves high carbon, tempering, and stabilization to eliminate internal stresses. They may contain chromium, manganese, silicon, vanadium, and tungsten.

Main Features of Gauge Blocks

• High degree of dimensional accuracy, flatness, and parallelism
• Strict surface fineness
• High surface hardness
• Low coefficient of thermal expansion
• Resistance to warping and rust

Vernier Caliper Measurement Standards

The caliber (or vernier caliper) is the linear measuring instrument most commonly used in the workshop. It can control external and internal length and depth measurements. Its accuracy typically ranges from 1/10 to 1/50 mm.

Main Parts of a Caliper

• Body size
• Slider (Vernier scale)
• Tips for external and internal measures
• Rod to measure depth
• Graduated scale in mm
• Graduated scale in inches
• Button to lock the cursor

These are constructed of stainless steel, which provides high resistance to deformation and wear. The most accurate gauge features a vernier divided into 50 parts.

External Micrometer Mechanics

The micrometer for external action consists of a movable shaft with a threaded portion, at the end of which a graduated drum is mounted. On the fixed line, there is a sleeve graduated in mm.

External Micrometer Parts

• Horseshoe arch (Frame)
• Fixed-point plane (Anvil)
• Mobile axis (Spindle) with a flat tip parallel to the fixed point
• Graduated body (Sleeve) with a scale in mm and 0.5mm
• Graduated drum (Thimble)
• Locking device

The thread of the micrometer screw has a pitch of 0.5mm; a full turn of the screw moves it 0.5mm forward or backward.