My job as a technician for Dixon Abrasives is to make sanding make sense. This is not as simple a task as most people would think. Every part of the sanding process must work together to accomplish a few simple tasks:
If the product coming through the wide belt machine is polished or smashed, it will feel smooth and shiny. It will not accept stain properly. In wipe stains certain pigments will wipe off. In spray stains the pigments will pool up on the surface and a darker color will result. You will notice that parts that have been hand sanded will often be patchy because the sanders will miss parts or not cover the whole surface evenly.
Swirls are also a result of smooth and shiny wide belt sanding. It is impossible to hand orbital sand a smooth and shiny surface without leaving scratch marks that show. This is the rotary swirl mark everyone tries to avoid. When wood is properly wide belt sanded, the scratch pattern sands away easily. I always say it melts away like butter. The hand sander should stop sanding once the little mountains of scratch are removed to avoid driving grains into the flat plane that has just been created. The more the flat plane is sanded the more swirls will result. If the hand sander is polishing the surface they will cause their own smooth and shiny surface to create swirls in. This concept is the real way to eliminate swirls.
If a sanding process breaks any of these principles it will cause issues. Many companies base their entire staining and coating process on very poor sanding. They fight forever to maintain color with an ever changing result. It can be incredibly frustrating to see a company trapped in a prison of their own design because they really never understood how to sand.
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