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(1)

Gauges

• Used for dimensional control of the component

• Gauges are used in mass production because

– Measuring dimensions is time consuming &

expensive

– Generally absolute measurement is not required

(2)

Classification of Gauges

According to: Types

Type/Use Standard gauge

Limit gauge

Application Workshop gauge

Inspection gauge

Master/Reference gauge

Form Plug gauge

Snap/ring gauge Design/Construction Fixed limit gauge

Indicating gauge Combination gauge Specific application Screw gauge

Radius gauge Filler gauge

(3)

Types of Gauges

• Workshop Gauges:

Used by the machine operator.

Designed to keep the size of the component near the centre line of the tolerance.

• Inspection Gauges:

Used by the inspectors for the final acceptance of manufactured components.

Have slightly larger tolerance than the workshop gauges

• Master Gauges/ Reference Gauges:

Used only for checking of other gauges.

Seldom used due to high cost

(4)

Indicating & Combination Gauges

• Indicating Gauges

Indicate the value of dimensions on a visual display system.

E.g. Dial gauge

Involve some magnification system.

For dimension control of a component, the pointer must lies between two prefixed points.

• Combination Gauges:

Specially designed to check more than one dimensions in a given setup.

(5)

Standard Gauges

• Made to the nominal size of the part to be tested

• Have the measuring member equal in size to the mean permissible dimension of the part to be checked.

• A standard gauge should mate with some

snugness.

(6)

Types of Standard Gauges

(7)

Radius or Fillet Gauge

Radius gauge are used to:

To check concave and convex radii on corners or shoulders.

For layout work and inspection of components.

As a template when grinding of cutting tools.

(8)

Thickness or Feeler Gauge

Uses:

Measurement of clearances between components

Setting small gaps

Determining fit between mating parts.

E.g. Adjusting the spark gap between the distributer points of an automobile.

Consists of a set of narrow strips

(12.5mm wide) with thickness marked on each strip.

Blades should neither be forced nor slide freely between the mating parts.

(9)

Screw Pitch Gauge

• Also called thread gauge

• Used for checking the pitch of a screw thread

• Available in metric & inch units

• Each blade has several teeth shaped to the standard thread form.

• Available with 55° and 60°

included thread angles.

(10)

Limit Gauges

• Check product dimensions w.r.t its maximum

& minimum acceptable limits

• Majority of gauges are in the form of limit gauges.

• Continually subject to abrasive wear

(11)

Limit gauges

(12)

Limit Gauges (Contd.)

• Advantages:

– Fast inspection

– Low dependence on operator skill

– More than one dimension can be checked simultaneously

– Economical

• Limitations:

– Exact dimension cannot be ascertained

– Accuracy of gauge declines with time due to wear

(13)

Desirable Properties of Gauge Materials

• Accuracy & service life are the most important characteristics of gauges.

• Gauge Materials must therefor possess:

– Wear resistance.

– Stability: to preserve size and shape – Corrosion resistance

– Good Machinability

– Low coefficient of expansion

(14)

Common Gauge Materials

High carbon steel:

Heat treated Cast steel (0.8-1% C) is commonly used for most gauges.

Mild steel:

Case hardened on the working surface Stable and easy to machine

Case hardened steel:

Used for small & medium sized gauges.

Chromium plated & Hard alloys:

Chromium plating imparts hardness, resistance to abrasion &

corrosion.

(15)

Common Gauge Materials

Cast Iron:

Used for bodies of frames of large gauges whose working surfaces are hard inserts of tool steel or cemented carbides.

Glass:

Free from corrosive effects due to perspiration from hands.

Not affected by temperature changes.

Invar:

It is a nickel-iron alloy (36% nickel)

Possesses a low coefficient of expansion Not suitable for usage over long periods.

(16)

Types of Limit Gauges

(17)

Snap Gauge

Used to check the accuracy of shafts

It has a U-Shaped frame with jaws

Snap gauge may be:

Single ended or double ended.

Fixed or with adjustable jaws.

Snap gauges are:

Light weight Easy to operate Sufficiently rigid

Permit interchangeability parts.

Available in the size of 150-600 mm with tubular frames

(18)

Pin Gauge

• Used to check holes larger than 75mm, such as automobile cylinder

• During measurement, the gauge is placed lengthwise across the cylinder bore.

• Especially useful in measurement of width of grooves or slots.

(19)

Plug Gauge

• Used to check the accuracy of holes.

• Used as sets of GO & NO GO gauges

• It should engage the hole to be checked without using pressure

• Should be able to stand in the hole without falling

(20)

Ring Gauge

• Used to check the shafts and male members.

• The “Go’ and ‘Not Go’

members may be separate or in a single ring.

• Ring gauges are of three types:

Plain ring gauge Taper ring gauge Thread ring gauge.

(21)

Limit Gauges

• Used for mass production

• May be used by unskilled workers

• Determine whether the size of a component lies within the prescribed limits.

• Do not determine the size of a part

(22)

Taylor’s Principle

• GO Gauge

Designed on the maximum material condition

Checks all dimensions of the work piece

GO plug gauges must have :

Full circular section

Length > 1.5 diameter to be tested

• NOT GO Gauge

Designed for the minimum material conditions

Checks only one dimension at a time

(23)

Gauge Tolerance

• Gauge Tolerance

– 10% of work tolerance

– Provided on the GO and NO GO gauges

• Wear allowance

– 10% of gauge tolerance

– Provided on the GO gauge only

– If gauge tolerance is less than 0.09 mm no wear allowance is provided

(24)

Disposition of Gauge Tolerance

(25)

Disadvantages of Workshop and Inspection Gauges.

• The workshop and inspection gauges are to be made separately as their tolerance zones

are different.

• Components within work tolerance limits may be rejected under workshop gauges. Therefore they are again checked using inspection gauges.

• Components not in work tolerance limits may be

accepted when tested by inspection gauges.

(26)

Revised Gauge Limits

• Tolerance zone of inspection gauge is reduced

• Workshop gauge tolerance remains the same.

• For ‘Go’ and ‘No Go’ inspection gauges in this system, the 110% of the range of work tolerance is covered

(27)

British System

(28)

Example

Design the general type of GO & NO GO gauges for components having 50 H7 d9 fit.

Given that:

Upper deviation of d shaft = -16D 0.44

50 mm falls in the diameter step of 30-50 mm

IT7 = 16i IT9 = 40i

Solution

i = 1.571 microns Hole:

Tolerance = 0.025mm;

Limits: 50 mm, 50.025 mm

Limits of GO Gauge: 50.000 mm, 50.0025 mm

Limits of NO GO Gauge: 50.0250 mm, 50.0225 mm Shaft:

Tolerance = 0.063 mm;

Fundamental dev. = - 0.080 mm Limits: 49.857 mm, 49.92 mm

Limits of GO Gauge: 49.9137 mm, 49.92 mm

Limits of NO GO Gauge: 49.8574 mm, 49.8637 mm

References

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