Abrasives and Sanding

Sanding plays a crucial role in woodworking, as do abrasives. As a woodworker, it is important to choose the right abrasive as it helps to:

  • Adjust size or remove excess material from saw cuts
  • Produce a flat, level surface
  • Hide or blend defects, dents, or scars
  • Round sharp corners and wood splinters
  • Remove scratches and tool marks from sawing, routing, or shaping
  • Prepare a new wood surface to accept glue, adhesive coating, varnish, or oil finish
  • Open up the surface by cutting across cellulose fibres, improving adhesion to coatings and glues
  • Remove undesirable or damaged coatings, or prepare for refinishing
  • Blend in joints such as scarf joints on moulding trim

Every workshop should have a supply of abrasive discs, sandpaper sheets, hook and loop or PSA abrasive discs, and abrasive belts for their finishing needs. Essential abrasive power tools include sanders, portable disc sanders, portable belt sanders, edge sanders, and bench belt/disc sanders.

Why use abrasives?

For those who frequently finish or refinish concave shapes and complex contours, drum sanders, abrasive sponges, and contour sanding power tools are invaluable. Abrasive drum sleeves are necessary if you have a drum sander or a sanding drum mounted on a drill or drill press. Pneumatic, corded, and cordless tools can all perform well for most DIY applications.

bobbin sander

Abrasives -  Grits

A good range of grit sizes will enable the completion of tasks including dimensional changes, rough finishing, smoothing, flattening, fine sanding, and polishing. While it may seem counterintuitive, a larger abrasive grit number equates to a finer abrasive product. Grit size is based on how the abrasive grains on sandpaper pass through a series of test sieves or screens, designated by the number of wires per unit area. Hence, a 400 mesh size screen has much finer openings compared to a 50 mesh screen. A 400 grit abrasive disc produces finer finishes compared to a 220 grit product, while a 24 grit product produces much deeper scratches in wood compared to a 50 grit sleeve.

Abrasives - Considerations

Wood is softer and easier to abrade or sand compared to metal alloys, cement, or glass materials. However, wood sanding dust can load or clog the spaces between the abrasive grain particles. This eventually reduces or stops the abrasion process. A dull or loaded abrasive product will require extra operator muscle to sand and may leave dark “burn” marks on a surface. Stearate or wax-like anti-loading additive layers are used on the top surface of woodworking abrasives to prevent or delay loading. Some woodworking professionals might have concerns about their impact on subsequent varnish, adhesive, or paint adhesion.

The spacing of the abrasive grains on the surface can also affect loading. A closed coat abrasive has more abrasive grain per unit area, and the grains are closer together. Closed coat products are more aggressive and produce a better surface finish. Closed coat abrasives are almost always the best choice for sanding hardwoods like oak, maple, hickory, and ash. Pine, fir, spruce, cedar, redwood, and other softwoods have a greater tendency to load. An open or semi-open coat product has extra space between the grit particles, which might accommodate more sanding dust before loading.

Health and Safety Considerations

Always wear dust masks or respirators and eye protection when using abrasive products. Besides being a pervasive irritant to the respiratory system, the sanding dust of certain exotic hardwoods can be toxic. Abrasive belts for woodworking have conductive and anti-static layers to reduce or prevent triboelectric static charges and spark discharges from occurring.

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