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Chapter 8.0

Surface Plate Inspection

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Topics Objectives Explain the design and functions of surface plate State types and the advantages/disadvantages over

the said material Explain and perform the methods for maintaining the

surface plate Inspect complex linear measurements using various

techniques Identify the accessories or holding devices used in

conjunction with surface plate

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Contents Introduction Surface plate inspection Granite Surface Plate Inspection Standard Sizes and Grades Overall Flatness Comparison btwn Cast Iron & Granite. Care of Surface Plate. Sources of Errors Surface Plate Accessories or Holding Devices

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Part dimensions can be checked very precisely and accurately by means of the surface plate method in conjunction with many types of height gauges, measuring instruments and holding devices.

However, accurate measurements can only be maintained when the reference surfaces of the parts are established with respect to the surface plate which acts as a simulated datum or reference.

Thus, surface plates provide a true, flat reference surface for any types of dimensional measurements.

Introductions

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Surface plates are truly flat surfaces which are available in many sizes and difference accuracy.

Their surfaces are very accurately machined and well-polished.

It is used a reference plane or datum surface from which measuring and marking-out activities & etc.

Surface Plate Inspection

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Surface plate, that big, flat rock sitting in your temperature-controlled inspection lab, is the foundation of dimensional measurements stand.

Selecting and caring for a granite surface plate is key to ensuring that your products’ dimensional specifications are as accurate as possible.

Generally they are made of 2 types of materials: cast iron granite stone

Surface Plate Inspection (cont)

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All of the granites have been carefully measured to establish the modulus of elasticity, allowing us to comply with the federal specifications and user requirements

Granite Surface Plate Insp.

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Granite surface plates provide an accurate reference plane for work inspection and for work layout.

Their high degree of flatness, overall quality and workmanship also make them ideal bases for mounting sophisticated mechanical, electronic and optical gauging systems

Granite Surface Plate Insp. (cont)

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0-Ledge - for economy and stability

2-Ledge Granite Surface Plate

Standard Sizes and Grades

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4-Ledge Granite Surface Plate

p/s : Plates with ledges are for work clamping purposes only

Standard Sizes and Grades

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Three standard grades of tolerance for surface plates as follows:

• AA - Laboratory Grade: For high precision operations in consistent temperature gauging rooms and metrology departments

• A - Inspection Grade: For general use in quality control areas

• B - Toolroom Grade: For shop work and production checking

Overall Flatness

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Cast Iron GraniteWear quality Good Good

Stability Excellent Excellent

Rigidity Excellent Excellent

Effect of moisture X rust (x distort) X rust (may distort)

Shape and size Limited Almost unlimited

Heat absorption Fast absorb, slow dissipate Slow absorption & dissipate

Heat radiation Reflect Absorb

Cost High Low

Comparison btwn Cast Iron & Granite.

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Care of Surface Plat Do not abuse surface plates; they are precision tools. Clean entirely the surface plate before and after use

with soap and water or alcohol. Part should be deburred and clean before they are

placed onto the surface plate. Do not allow unnecessary objects or tools to be placed

on the surface plate. Do not drop any objects onto the surface plate. Keep the surface plate covered when it is not used.

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Care of Surface Plate. (cont)CLEANERS Keeping your precision granite products clean

and in the best condition can lengthen your calibration intervals and help ensure that your readings are accurate.

Two types of cleaner: liquid and waterless. Pink liquid cleaner is furnished in plastic bottles. Waterless cleaner is a product that is extremely

popular. The waterless cleaner is packaged in 1-pound containers, with there being (12) per case

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Care of Surface Plate. (cont)

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Care of Surface Plate. (cont)

SURFACE PLATE COVERS Usage of surface plate covers to protect your

precision granite investment. Prevent abrasive build up on your plates with

covers made from heavy gauge black vinyl with a soft interior lining.

Covers provide a tough, durable, protective outside with a soft cushion inside

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Care of Surface Plate. (cont)

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Sources of Errors Eventually wear may cause loss of accuracy,

but this takes quite some time. A workpiece which has burrs and dirt will cause

poor readings as well as increasing unnecessary wear.

More…

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Surface Plate Accessories and Holding Devices

A Surface Plate must always be used in conjunction with numerous measuring instruments, accessories and holding devices

The commonly and widely used accessories or holding devices to the surface plate are :

# vernier height gauge, # dial gauge, # gauge blocks, # parallel bars, # V-block, # angle plate, sine-bar, # precision vice, # precision try-square, cylindrical pin, # and etc.

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Surface Plate Accessories and Holding Devices (cont)

They must be kept clean and free from burrs and nicks.

When necessary a fine stone can be used to clean and remove burrs. The prime concern is their flatness, squareness and parallelism.

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Surface Plate Accessories and Holding Devices (cont)

Vernier Height Gauge Types of Height Gauges

vernier height gauge dial height gauge digital height gauge

self-supporting measuring instrument which consists of a heavy base with a vertical vernierused in conjunction with a surface plate for marking or lay-out the workpiece when the scriber is attached

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Surface Plate Accessories and Holding Devices (cont)

• A dial gauge attached to the height gauge to provide greater accuracy in measurement - comparative method with the help of a Master Height Gauge.

Base – ensure rigidity and stability• Ground & lapped to an accuracy 0.005mm.

Beam Measuring jaw & scriber Graduation Slider

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Surface Plate Accessories and Holding Devices (cont)

• Sources of errors The slide arm is not parallel with the base. An unclean and damaged base causes inaccuracy. The scriber is worn-out. The height gauge is not calibrated properly.

• When you check for accuracy always ensures that the zero mark of the vernier and main scale coincide when the base of the scriber makes contact flat with the surface plate.

• Alternatively we can use a gauge block and compare it with the scale of the height gauge

Avoid parallax errors. When you read the measured value, always look vertical to the scale .

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Surface Plate Accessories and Holding Devices (cont)

• Guidelines for using a Vernier Height Gauge Always ensure that the height gauge had been

calibrated. Clean the height gauge and surface plate entirely

before use. Hold the base firmly to the surface plate to avoid

tipping. Always lock the main scale when in use. Move the height gauge slowly and gently. Do not slam

it around. Clamp the scriber as near as possible to the column.

This will increase accuracy and less vibration. A dial gauge may be attached to provide greater

accuracy.

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Surface Plate Accessories and Holding Devices (cont)

• Principle of Surface Plate Inspection To inspect the height or length of the

workpiece To inspect hole location of the part To inspect a workpiece using vernier height

gauge and dial gauge To inspect the part using transfer method

(comparative)

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Surface Plate Accessories and Holding Devices (cont)

Parallel Barmade of harden tool steel and rectangular in shape

which come in different sizes. They are machined very accurately in such a way

that the surfaces are parallel, straight and squared to each other.

used in conjunction with a surface plate for stack-up or supporting the workpiece to establish the reference the reference surfaces

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Surface Plate Accessories and Holding Devices (cont)

Angle Block/PlateThey are used to hold and locate the work piece

vertical to the surface plate. They are made of cast iron and machined very

accurately to maintain the squareness and flatness.They can also be used to check the squareness of

the work piece by means of light gap Two grades – Grade 1 & Grade 2 (flatness,

squareness, parallelism)

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Surface Plate Accessories and Holding Devices (cont)

V-Block used for checking out the roundness of cylindrical

work piece & marking center accurately before use V-block :

Check visually / finger – dents, edge nicks, scratches, burrs (damage surface plate, cause V-block to tilted imperceptibility from true flat or vertical.