The goal of all brush sanding is to break edges, both inner and outer, leading and trailing, along with the ability to sand 3D parts such as the five-panel door manufacture and yacht construction industries.
Parts run through a brush machine not only have the edges broken but also benefit from sanding loose wood fibers in the profiled areas. Breaking or softening the 90 degree edges or corners is done because an edge will not hold any stain or sealer coat. If the edges aren’t broken, air and moisture can get in under the coating and can leads to cracks and peeling of the finish. The edge breaking process improves lacquer/sealer adhesion while at the same time reducing the amount of material required. Edges that have been “broken” will accept a more even coating of sealer, reduce the amount of sealer used and provide an upgraded product over previous methods. The amount of sealer material is reduced by eliminating typical over coating when work pieces have sharp edges.
Brush sanding upgrades the previous face sanding by also sanding into the profile which provides for more uniform staining results on all surfaces. Fiber removal provides a much smoother work piece. The abrasives work deep into the profiles to shorten the wood fibers to more closely match the surface sanded areas and greatly improve the after sealer-sanded results. Lacquer, or sealer coats, do not adhere evenly to sharp edges and tend to flow away from the sharp edges.
A rule of thumb is if the part can be roll coated then it needs to be wide belt sanded, and if the part has to go through a spray booth then it will need to be brush sanded. One added advantage is that if you purchase a brush sander from a sanding machine manufacturer, you can get a combination machine with brushes and normal wide belt heads in the same machine.