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Possible Reasons for Streaking of a Workpiece
- The belt is loaded or dull.
- Contact roll may be too aggressive or hard.
- The sanding pressure is too high. On platens, excessive pressure will cause streaking, which is shiny and white (1.5 inches or more). Usually, the streaking is straight. Wavy streaking (longitudinally) is caused by belt oscillation (snakemarks).
- The belt tension is too low.
- Contamination of platen surface or contact roll.
- The felt layer on the platen may be compacted.
- 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 on the surface of the contact roll can cause raised areas on the workpiece.
- Sanding dust or loose graphite is between the belt and the contact roll or platen.
- Damaged abrasive belt. i.e., inclusions of loose grit, resin, or other foreign matter.
- Excessive out-feed hold-down shoe pressure is generally seen as straight streaks.
- Damaged graphite cover on platen.
- Hand sand the cover with 100 or 120-grit material to re-establish a smooth surface.
- The abrasive material is defective.
- Oscillation mechanisms are out of adjustment.
- 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.
- There is dust on the workpiece or resin spots in wood.
- Static electricity buildup, machine improperly grounded, or low humidity. Streaking of this nature is usually very narrow in width (1/16" or less) and is intermittent.
- There is overloading due to glue lines, pitch, or tramp material on the workpiece. This causes belt burning.
- Improper belt mounting can cause slight creasing. (Check handling procedures)
Possible Reasons for Scratching of a Workpiece
- Grit is too coarse for application.
- The platen surface is uneven or tilted. High or low platen surface.
- The abrasive belt is too narrow for the pressure shoe.
- Improper grit sequence. Previous grit scratch not being removed.
- Loose grit from another operation getting into the sanding area.
- Contamination on abrasive belt surface.