Surface Finish Measurement: Interpreting Symbols and Using Surface Indicators, Lecture notes of Analytical Geometry and Calculus

Download Surface Finish Measurement: Interpreting Symbols and Using Surface Indicators and more Lecture notes Analytical Geometry and Calculus in PDF only on Docsity!

Surface Finish

Measurement

Objectives

• Interpret the surface finish symbols that appear on a drawing
• Use a surface finish indicator to measure the surface finish of a part

Surface Indicator

• Tracer head and amplifier
• Tracer head has diamond stylus, point radius. μin that bears against work surface
• Movement caused by surface irregularities converted into electrical fluctuations
• Signals magnified by amplifier and registered on meter
• Reading indicates average height of surface

Readings

Either arithmetic average

roughness height (Ra) or root mean square (Rq)

Surface Finish Definitions

• Surface deviations: departures from nominal surface in form of waviness, roughness, flaws, lay, and profile
• Waviness: surface irregularities that deviate from mean surface in form of waves
• Waviness height: peak-to-valley distance in inches or millimeters
• Waviness width: distance between successive waviness peaks or valleys in inches or millimeters

Surface Finish Definitions

• Roughness: relatively finely spaced irregularities superimposed on waviness pattern - Caused by cutting tool or abrasive grain action - Irregularities narrower than waviness pattern
• Roughness height: Ra deviation measured normal to centerline in microinches or μm
• Roughness width: distance between successive roughness peaks parallel to nominal surface in inches or millimeters
• Profile: contour of specified section through a surface

Symbols that Indicate Direction of Lay

|| Parallel to boundary line of surface indicated by symbol | Perpendicular to boundary line of surface indicated by symbol X Angular in both directions on surface indicated by symbol M Multidirectional C Approximately circular to center of the surface indicated by symbol R Approximately radial in relation to the center of surface indicated by symbol

Average surface roughness produced by standard machining processes

Microinches Micrometers

Turning 100–250 2.5–6.

Drilling 100–200 2.5–5.

Reaming 50–150 1.3–3.

Grinding 20–100 0.5–2.

Honing 5–20 0.13–0.

Lapping 1–10 0.025–0.

To Measure Surface Finish with a

Surface Indicator

5. Thoroughly clean surface to be measured
   • Ensures accurate readings
   • Reduces wear on rider cap protecting stylus
6. Using smooth, steady movement of stylus, trace work surface at approximately .125 in./s
7. Note reading from meter scale

Other Methods

• Surface analyzer
  • Uses recording device to reproduce surface irregularities on graduated chart, providing ink-line record
• Comparison blocks
  • Used for comparing finish on workpiece with calibrated finish on test block using fingernail test
• Commercial sets of standard finished specimens
  • Up to 25 different surface finish samples