Gauges

Gauging involves checking parts with various gauges. Gauging simply shows whether the piece is made within

the specified tolerances.

Examples of Gauges: plug gauges, ring gauges, snap gauge, thread gauge, and optical gauges..

Fixed Gauges

Figure 35.10 (a) Plug gauge for holes with GO and NOT GO on opposite ends. (b) Plug gauge with GO and NOT GO on one end. (c) Plain ring gauges for gauging round rods. Note the difference in knurled surfaces to identify the two gauges. (d) Snap gauge with adjustable anvils.

Plug Gauge

Plug gauges are used to check whether hole diameters are within specified tolerances.

A double end cylindrical plug gauge has two gauging members known as go and no-go plugs.

The go plug should enter the hole with little or no interference. The no-go plug should not fit.

Ring Gauge

External diameters are checked with ring gauges.

The go and no-go ring gauges are separate units, and can be distinguished from each other by a groove cut on the knurled outer surface of the no-go gauge.

Snap Gauge

A nonadjustable snap gage is made for one specific size.

An adjustable snap gauge can be adjusted through a range of sizes.

A snap gauge serves the same purpose as a ring gauge. Snap gauges are designed to check internal diameters, external diameters, or both. There are three general types:

A dial indicator snap gauge measures the amount of variation in the part measurement .

Thread gauges

Coating Thickness Gauges

Form Gauges

• Radious gauge • Width gauge

Feeler gauges are mostly used in engineering to measure the clearance between two parts.They consist of a number of small lengths of steel of different thicknesses with measurements marked on each piece.

Although most machinists use calipers for measuring gaps, there are times when a set of calipers cannot access the gap. One end is lined up with the zero mark on the ruler, and the person doing the measuring simply observes where the other point lands

Feeler Gauge

Applications

Pin & Wire gauge Measuring PinsThread Measuring Wires

Basic Measurement Devices

Surface plates Sine centre V-block Mandrels

Surface plate

Surface Plates

• Cast-iron plates– Well ribbed and high strength– Good wear-resistance qualities– After machined, surface scraped by hand to flat

• Operation long and cost high• Granite surface plates

– Manufactured from gray, pink, or black granite– Several degrees of accuracy– Extremely flat finishes produced by lapping

Advantages of Granite Plates

• Not appreciably affected by temperature change• Will not burr, therefore, accuracy not impaired• Nonmagnetic• Rustproof• Abrasives will not embed themselves as easily in the surface

Care of Surface Plates

• Keep surface plates clean at all times• Clean occasionally with solvent to remove film• Protect with wooden cover when not in use• Use parallels whenever possible to prevent damage to plates by rough parts or

castings• Remove burrs from workpiece before placing it on plate• Slide heavy parts onto the plate rather than place them directly on the plate• Remove all burrs from cast-iron plates by honing• When not in regular use, cover cast-iron plates with thin film of oil to prevent rusting• Center punching or prick punching layout lines should not be done on a surface plate

Sine centre

mandrel

V block