26-05 Demo: Abrasives by Dennis Cahill

‍ ‍Abrasives in Turning

Dennis Cahill was our May club demonstrator who covered everything we want to know about abrasives.  

Safety: Respiratory safety is of the utmost importance while sanding and use of filter masks, such as a P100, should be considered. 

• Anatomy of Sandpaper: It is no longer just sand glued to paper but includes  materials such as aluminum oxides and silicon carbides.  Sandpaper life is shortened by head and solvents (eg. Water, mineral oil). 

• Prolonging life (of sandpaper):  Sand at the slowest lathe speed and use gentle pressure. 

• Size: For sandpaper selection, remember that the smaller the number the bigger the particle size.  Generally, start with the lowest grit needed (this fixes tear-out or can refine a shape).  

• Power vs manual: 

  • Power sanders or friction sanders help blend in scratches by creating a random pattern

  • Manual sanding often creates  straight lines 

  • Assess your sanding using a light source at a low angle to help reveal scratch patterns 

• Places to purchase (at a bargain): Kilingspor bargain boxes - 10lbs for $19, 20lbs for $35. 

• Customizing sanding discs: cloth backed rolls allow for cutting custom sanding discs (especially for hook and loop handheld sanders) which ends up being more economical than buying pre-cut discs. 

• Sanding mesh (Abranet): 

  • Advantages: Many holes allows for better clearance of dust makes it longer lasting

  • Disadvantages: Can be expensive

• Best practices using sandpaper on a lathe: 

  • Slow down the speed of the lathe (high speed = heat)

  • Reverse the direction of the lathe = better visibility and control when sanding 

    • Be careful not to unscrew the piece from the chuck/face plate

• Surface preparation: 

  • Wipe down turned piece with rubbing alcohol or mineral spirits to raise the grain, then sand (working up in grit size to achieve desired smooth finish) 

• Sanding sealer: Seals the woods and stiffens the fibers to make the abrasive grit more effective. Sealer prevents wax from penetrating too deeply into the wood and therefore can be stripped off with a solvent if needed. 

• Other abrasives: 

  • Steel wool: can be a useful intermediate step (or even fine abrasive), especially with polyurethane.  Use care cleaning to avoid rust stains from metal fibers especially on light woods. 

    • Ebonizing effect: dissolve steel wool in vinegar

  • Scotchbrite: use in same manner as steel wool, but easier to handle 

• Sanding in narrow spaces: use creativity to make homemade tools such as a champagne cork on a dowel padded and secured with superglue to sand deep inside a piece, or creating a disc sander by mounting a round piece of wood onto an old face place. 

• Cleaning sandpaper: A “sandpaper eraser” is essentially solidified rubber cement.  This cleans the grit of the sandpaper. 

• Sanding with solvents: Helps to eliminate dust.  Ensure the solvent will not dissolve the adhesive. Be careful to dispose of appropriately after laying out to dry on concrete as rags soaked with oil-based solvents or tung oil can spontaneously combust. Never dispose of with sawdust or wood shavings. 

• Sharpening tools: the abrasives must be stronger than the material they are used on 

  • Diamond wheels for carbide tools 

  • CBN for high speed steel tools

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