Using Rubber Disc and Drum Sanders
Sanding, always a tedious task, can be speeded up by the intelligent use of power tools. The most common attachment is the flexible rubber backing disc to which discs of abrasive paper are screwed. Disc sanders are also available as integral tools and as attachments to turning lathes.
Ideally, timber should always be sanded along the grain direction, and disc sanders inevitably break this golden rule. For this reason a more satisfactory appliance is the belt sander. This is usually an integral tool which consists of a moving abrasive belt tensioned between two drive rollers. The nearest equivalent in power tool attachments is the drum sander, which also allows with-the-grain sanding.
Because of their rotary action, sanding discs must be used very carefully to avoid undue circular marking of the surface. It is usually best to complete the coarse sanding with a disc, working from coarse to medium grade abrasive papers, and then to complete the fine sanding by hand.
Never attempt to use the whole surface of the disc, as this will inevitably leave deep and difficult-to-remove circular marks.
Tilt the disc at an angle of 30° so that only one-third of its area is in contact with the work. Too much downward pressure may cause overloading. Keep the sanding action light, always working with a sweeping movement of the tool.
Disc sanders will not remove paint because the heat generated causes it to melt, forcing it further into the timber and clogging the abrasive paper. Avoid sanding over sharp edges which will snag and tear the sanding discs.
The drum sander, consisting of a foam-rubber wheel with an abrasive ‘tyre’, can be used on convex, concave and flat surfaces. Its action in removing waste is not as effective as the disc sander’s but it does have the important advantage of being able to work in the direction of the grain The abrasive belt or tyre is held to the foam-rubber wheel with spots of non-hardeningapplied to the non-abrasive side. The bond tends to fail after some time. When the abrasive belt starts to slip, more must be applied. As with the disc sander, light pressure gives the best results.
Abrasives for use with power sanders include ordinary glass- or sandpapers and the garnet-papers which have better durability and performance. Even better are the more expensive aluminium oxide papers.
The printed numbers on the back of abrasive papers denote the number of grit particles per square inch. Thus a coarse `40’ grade paper will have 40 particles in 25 mm square (square inch) and a fine ‘80’ paper 80. When ordering abrasive discs or belts, always state the grade numbers required. Store abrasives in a dry place as damp, and even atmospheric humidity, can make them useless.