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Abrasive Troubleshooting

Streaking & Scratching Workpiece

Possible reasons for streaking of a workpiece:
  1. Belt is loaded or dull.
  2. Contact roll may be too aggressive or hard.
  3. Sanding pressure is too high. On platens, excessive pressure will cause streaking, which is shiny and white (1.5 inch or more). Normally, the streaking is straight. Wavy streaking (longitudinally) is caused by belt oscillation (snakemarks).
  4. Belt tension is too low.
  5. Contamination of platen surface or contact roll.
    • Felt layer on platen may be compacted.
  6. Contact roll face damaged or worn.
    • This is often caused by feeding the workpieces unequally across the width of the belt, causing uneven wear. Always process the widest pieces first.
    • Grooves worn in surface of the contact roll can cause raised areas on the workpiece.
  7. Sanding dust or loose graphite is between the belt and contact roll or platen.
  8. Damaged abrasive belt. i.e. inclusions of loose grit, resin, or other foreign matter.
  9. Excessive out-feed hold-down shoe pressure, normally seen as straight streaks.
  10. Damaged graphite cover on platen.
    • Hand sand the cover with 100 or 120 grit material to re-establish a smooth surface.
  11. Abrasive material is defective.
  12. Oscillation mechanisms are out of adjustment.
  13. Needle-shaped streaks or hairlines are often caused by inclusions of sand, resin, grit, or minerals in the workpiece. These inclusions can damage the grit or backing sides of the belt.
  14. There is dust on the workpiece or resin spots in wood.
  15. Static electricity buildup, machine improperly grounded or low humidity. Streaking off this nature is normally very narrow in width (1/16" or less) and is intermittent.
  16. Overloading due to glue lines, pitch, or tramp material on workpiece. This causes belt burning.
  17. Improper belt mounting can cause slight creasing. (Check handling procedures)
Possible reasons for scratching of a workpiece:
  1. Grit is too coarse for application.
  2. Platen surface is uneven or tilted. High or low platen surface.
  3. Abrasive belt is too narrow for pressure shoe.
  4. Improper grit sequence. Previous grit scratch not being removed.
  5. Loose grit from another operation getting into sanding area.
  6. Contamination on abrasive belt surface.
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