Marlborough Boys College 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 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

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)

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 finer the texture the greater the cost to produce

Surface Texture Terms

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

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

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

Lay Plane of Projection Lay is the dominate pattern of marks left on the surface arising from machining processes (tool type, feed rate, and machine type) Indicated by symbol Plane of Projection Parallel Perpendicular Diagonal Multi Circular Radial

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

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

Ra (Micrometers) = A¹+A²+A³+….+An Cut off length 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+….+An Cut off length Micrometers = 0.000001 meters = 1 x 10-6 meters

Roughness Grade Numbers Roughness Average in Micro meters (Ra) can also be expressed as a Roughness Grade Number (N) Ra N 50 Um N 12 25 Um N 11 12.5 Um N 10 6.3 Um N 9 3.2 Um N 8 1.6 Um N 7 Ra N 0.8 Um N 6 0.4 Um N 5 0.2 Um N 4 0.1 Um N 3 0.05 Um N 2 0.025 Um N 1

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

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

Lay Symbols

Average Values For Processes in µm 50 25 12.5 6.3 3.2 1.6 0.8 0.4 0.2 0.1 0.05 0.025 Gas Cutting   Shaping Drilling Milling Reaming Turning Grinding Lapping Average Possible For More Detailed Information

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

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

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

Further Information Sites Virtual Machine Shop Cyberman

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