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Chapter 8.0

Chapter 8.0. Surface Plate Inspection. 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

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Chapter 8.0

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  1. Chapter 8.0 Surface Plate Inspection

  2. 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

  3. 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

  4. Introductions • Part dimensions can be checkedvery 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 surfaceplate which acts as a simulated datum or reference. • Thus, surface plates provide a true, flat reference surface for any types of dimensional measurements.

  5. Surface Plate Inspection • 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.

  6. Surface Plate Inspection (cont) • 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

  7. Granite Surface Plate Insp. • 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

  8. Granite Surface Plate Insp. (cont) • 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

  9. Standard Sizes and Grades • 0-Ledge - for economy and stability • 2-Ledge Granite Surface Plate

  10. Standard Sizes and Grades • 4-Ledge Granite Surface Plate p/s : Plates with ledges are for work clamping purposes only

  11. Overall Flatness • 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

  12. Comparison btwn Cast Iron & Granite.

  13. 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.

  14. 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

  15. Care of Surface Plate. (cont)

  16. 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

  17. Care of Surface Plate. (cont)

  18. 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…

  19. 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.

  20. 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.

  21. 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 vernier • used in conjunction with a surface plate for marking or lay-out the workpiece when the scriber is attached

  22. 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

  23. 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 .

  24. 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.

  25. 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)

  26. Surface Plate Accessories and Holding Devices (cont) • Parallel Bar • made 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

  27. Surface Plate Accessories and Holding Devices (cont) • Angle Block/Plate • They 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)

  28. 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.

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