Screw Gauge

A screw gauge is a mechanical tool that measures the diameter, radius, or thickness of a thin wire or metal sheet precisely. A micrometre screw gauge is another name for it. It has two scales, one for pitch and one for circular motion. In comparison to the Vernier Caliper Scale, micrometre gauges are extremely accurate for measurement. A Micrometre and an Inch Micrometre can be used to measure screw gauge. A screw gauge is a tool used to precisely measure a cylindrical or spherical object. The screw gauge is primarily composed of a U-shaped frame and a spindle (or screw) attached to a thimble.

What is a Screw Gauge?

A screw gauge is a measuring instrument made of a calibrated screw that is used to measure the dimensions of small objects. A screw gauge is a meteorological instrument that is commonly used in machining and mechanical engineering. Screw gauges are used to precisely measure thin wires and sheets. It is divided into two scales: the Pitch Scale and the Circular Scale.

• The pitch scale is the primary scale used to calculate the distance travelled by the spindle per revolution (in millimetres). The instrument's barrel is engraved with vertical lines.
• The thimble has a circular scale engraved horizontally. A circular scale revolution corresponds to about half a millimetre of screw displacement.

Screw Gauge Measurement Using Micrometre

Learn about the construction of a Screw Gauge: Some sections, such as the Sleeve, Anvil, Spindle, Thimble Lock, Frame, Thimble, and Ratchet Stop, are movable, while others are fixed.

• Clean the spindle and anvil before beginning to measure: Place a piece of paper or a clean cloth between the spindle and the anvil. Tighten the setup slightly until the paper or cloth becomes jammed, then pull it out while cleaning the setup. This step is optional, but it aids in obtaining an accurate measurement because precision is essential.
• Place the object carefully between the anvil and the spindle: Place the object carefully between the anvil and the spindle. Because the anvil is inherently stationary, place the object against it. The object should be properly placed so that it does not move while being measured.
• To tighten, rotate the ratchet counter clockwise, making sure that the thimbles zero are parallel to the scale line on the sleeve.
• Tighten the spindle with the object in the middle: When rotated, the thimble clicks. Apply enough
• force until it clicks three times.
• While the object is in between, secure the thimble: Even if the thimble is locked, the spindle can be moved. This will assist you in getting an accurate measurement.
• Remove the object with caution: The accuracy of the screw gauge can be compromised if it is scratched or shaken, so avoid doing so.
• Take note of the reading before you unlock the spindle: If the single setup becomes loose, remeasure the entire setup.

Screw Gauge Measurement Using Inch Micrometre

The screw gauge measurement using an inch micrometre can be done by:

• Different thimble scales: The thimble has several distinct scales: In decimal notation, one hundred thousand is one-tenth of an inch, or 0.100. There are three lines between the numbers that are equal to twenty-five thousandths of an inch, which is expressed in decimal as 0.025.
• The equally spaced lines represent one thousandth of an inch, denoted in decimal notation as 0.001.
• Sleeves are numbered in whole numbers: The whole number scale defined by the lines on the sleeve represents a measurement of ten-thousandths of an inch, which is expressed in decimal notation as 0.0001. The number at the end represents a thousandth representation. If the last digit is 6, for example, the final representation is 0.500.
• Take note of the number of lines following the whole number: Note the markings next to the 100,000th mark and multiply by 0.25.
• Take note of the marking that corresponds to the thimble scale marking: Take note of the marking closest to it and directly beneath the measurement line.
• Add the figures: The screw gauge formula should be used to add the three numbers that were noted down in the previous step.

Working Principle of Screw Gauge

Screw gauges work on the screw principle. The screw gauge formula converts smaller distances to larger distances by measuring the rotation of the screw. Screw gauge measurement is based on two parameters: pitch and least count.

• The pitch of the screw gauge is defined as the ratio of the moved distance to the number of rotations.
• The screw gauge least count is the ratio of pitch to the total number of divisions on the circular scale.

A differential screw is an important component of an analogue screw gauge because it allows for small magnitudes. When spun one at a time, the threads on these screws correspond to axial movement. That is, each 360-degree rotation of the screw covers a small axial distance.

• This distance is known as the screw's lead or screw gauge pitch. Even if the object being measured is small, the size can be determined by turning the thimble, which rotates the screw.
• The minute dimension is converted into larger rotations that are much easier to understand.
• The measured wire dimension is displayed on an LCD screen in digital screw gauges.

Screw Gauge Formula

Every screw gauge employs two parameters. They are screw gauge pitch and least count.

• Pitch: The screw gauge's pitch is defined as the distance moved by the spindle per revolution, which is measured by moving the head scale over the pitch scale to complete one full rotation.

• The screw's least count is defined as the distance moved by the tip of the screw when it is turned through one division of the head scale.

A micrometre screw gauge is an instrument used to measure the diameter of thin wires and the thickness of small sheets of glass or plastics.

What is a Positive Zero Error?

When the dial and spindle of a micrometre screw gauge are brought together, the circular scale's zero mark is below the central scale line, indicating a positive zero error.

Positive zero error can be calculated using the division on the circular scale that corresponds with the main scale line. Optical errors are calculated by multiplying the number of divisions on the main scale line by the micrometre screw gauge's lowest count. To obtain the correct result, subtract this error from the total reading.

• When the zero mark on the circular scale is higher than the scale line on the anvil and spindle of a micrometre screw gauge, the zero error is said to be negative.

Negative zero errors in the circular scale (C.S.R.) can be found by inspecting the division on the main scale line. The product of the number of divisions of a circular scale based on the main scale line and the smallest count of the micrometre screw gauge equals the negative error. To obtain the correct result, this error must be added to the overall reading.

What is a Back Lash Error?

Because of thread wear and tear, the tip of the screw may not rotate completely backward during the reverse rotation of the head. Backlash is a term used to describe this phenomenon. When holding an object between anvil and spindle, do not rotate the head in the opposite direction. This will prevent backlash.

Uses of Screw Gauge

Screw gauge has several applications, including the following:

• A screw gauge is used to measure the diameter of circular objects, primarily wires, with an accuracy of 0.001cm.
• A screw gauge can be used to determine the radius of wires and other circular objects.
• A screw gauge can also be used to measure the thickness of paper.
• A screw gauge can be used to determine the thickness of metal sheets and glass slabs.
• A screw gauge can be used to determine the uniform thickness of any shape.

Things to Remember

• A screw gauge is a measuring instrument made of a calibrated screw that is used to measure the dimensions of small objects.
• Micrometres and inch micrometres can be used to measure screw gauges.
• A screw gauge is used to measure the diameter and radius of any metal sheet. It's a U-shaped tool with one end screwed on.
• Two parameters are used for measurement in every screw gauge. They represent the screw gauge's pitch and lowest count.
• The pitch is defined as the ratio of the distance moved to the number of rotations.
  • (distance)/ (pitch) (no. of rotations given).
• The least count is the ratio of pitch to the total number of divisions on the circular scale.
  • Least number of pitches = (pitch)/ (total no. of divisions on the circular scale).