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Surface Texture

Surface Texture. http://youtu.be/bl5rRmfdIaw?list=UUex9HyH13mgYPNu6Xo2s-xQ G Lancaster Marlborough Boys College. Contents. Definition Surface texture effects Terms Ra or CLA Roughness Grade Numbers Basic symbol for use on drawings Drawing Symbol Notation Lay symbols

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Surface Texture

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  1. Surface Texture http://youtu.be/bl5rRmfdIaw?list=UUex9HyH13mgYPNu6Xo2s-xQ G Lancaster Marlborough Boys College

  2. Contents • Definition • Surface texture effects • Terms • Ra or CLA • Roughness Grade Numbers • Basic symbol for use on drawings • Drawing Symbol Notation • Lay symbols • Average values for various processes • Other roughness values • Methods of testing • W W W References All underlined text acts as hyperlinks to indicated topic. Press Esc at any point to exit presentation Back One Last At Contents Page Forward One

  3. Definitions • Surface texture describes the variation of the surface from a perfect surface • Surface texture is made up of Roughness Waviness. Lay Flaws It is the topography of the surface The term surface texture is preferable to surface finish as surface finish implies coatings and finishing techniques (Painting, chrome plating etc)

  4. Surface Texture Effects • The appearance • The finer the texture the higher the aesthetic value • The function • Some functions require a fine texture • The dimensional tolerances possible • The finer the texture the greater the degree of dimensional accuracy possible • The cost • The finerthe texture the greater the cost to produce

  5. Surface Texture Terms

  6. Roughness • The closely spaced peaks and valleys produced by the machining process

  7. Waviness • Repeated widely spaced irregularities generally resulting from machine vibrations of chatter in th emachine

  8. Profile Profile is the shape of the surface It is made up of roughness and weariness. Profile is influenced by the tool type and shape

  9. Lay Lay is the dominate pattern of marks left on the surfacearising frommachining processes (tool type, feed rate, and machine type) Indicated by symbol Plane of Projection Parallel Perpendicular Diagonal Multi Circular Radial

  10. Flaws • Discrete or irregular infrequent irregularities these could be scratches, pits or cracks

  11. Errors of Form • Long form or non cyclic deviations in surface profile produced by errors in machine ways, slides or alignments

  12. Ra or CLA Sample Length The Ra (Roughness Average) or CLA (Centre Line Average) is the average distance from the centre line to the highest or lowest point. The Ra or CLA can be found by using the formula Ra (Micrometers) = A¹+A²+A³+….+AnCut off length Micrometers = 0.000001 meters = 1 x 10-6 meters

  13. Roughness Grade Numbers Roughness Average in Micro meters (Ra) can also be expressed as a Roughness Grade Number (N)

  14. Drawing Symbols Symbol has an angle of 60 degrees and an open top with two uneven sides. Basic shaped symbol. Machining optional Machine finish required This symbol has a bar added to the top of the standard shaped symbol. Removal of material not permitted This symbol is a basic shaped symbol with a circle added in the groove. Basic symbol with a bar added to the top of the right hand line. Special surface feature required

  15. Drawing Symbol Notation = Production Method Roughness Grade Number or Roughness Average = C= Sampling Length (f)= Other Roughness Values Machining Allowance = = Direction of Layusing Lay Symbols Click on labels for explanations of the notation

  16. Lay Symbols

  17. Average Values For Processes For More Detailed Information

  18. Machining Allowance • This is the amount of material that can be removed to achieve desired surface texture

  19. Other Roughness Values • Rp : is the height of the highest peak in the roughness profile over the evaluation length    • Rv is the depth of the deepest valley in the roughness profile over the evaluation length .   • Rt, is the sum of these two,or the vertical distance from the deepest valley to the highest peak. • Rz is the sum of the height of the highest peak plus the lowest valley depth within a sampling length

  20. Methods of Testing • Scratch comparison plates. • Each machining process requires it own set. • Optical and mechanical

  21. Information Sites • Virtual Machine Shop • Cyberman PDF files • Surface Texture Symbols and How To Apply • Notes USA Standards • Drawing Standards

  22. References • http://www.roymech.co.uk/Useful_Tables/Surface_Texture/Surface_Texture_index.html

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