Whether sanding by hand or using electronic assistance, use of the correct paper and technique will impact on your end result
By Gareth Greathead
Many home DIY chores such as painting gutters, resurfacing a door or maintaining wood require sanding. Electric sanders can save woodworkers hundreds of hours when it comes to the preparation of wood.
Sandpaper has a paper or fibre backing and comes in grits ranging from 40 (course) to 3000 (extra fine) and everything in between. The two most commonly used abrasive materials used to make sandpaper are silicone carbide (general purpose) and aluminium oxide (for wood). The silica used is derived from different sources and some are more appropriate than others for a particular application. Wet and dry paper resists clogging when sanding; the intended application will be marked on the back of the sandpaper and will indicate the applicable materials. The sandpaper used on electronic sanders is not the same as that on ordinary sheets of sandpaper. They normally have an additional coating that makes the disc, sheet or belt last longer.
The lower the number on the sandpaper, the coarser the particles and the deeper the scratches it imparts on the wood. Commonly available grits for electric sanders range from 80-240 grit. Sheets of sandpaper start at 60 grit and are available in grits as high as 3 000, and to obtain a smooth surface on wood, the use of steel wool is recommended.
Belt sanders are big, heavy and powerful tools that can remove a large amount of material quickly. At home a belt sander can be used to flatten a large, flat surface such as a door, deck or even hardwood floors. It is also good for removing paint and varnish. These machines are loud and can be dangerous if you aren’t careful.
Belt sanders use reinforced belts that form a continuous loop. Belt sanders come in three different sizes and the belts in a variety of lengths and widths. Larger machines and belts will be more aggressive than smaller sanders.
The general design consists of two cylindrical drums at the front and back of the sander. The one at the rear is powered by the motor and the one in front is free running and has a fine belt adjustment knob to help with belt tracking. There is normally a belt release lever on the open side of the sander for replacement of belts. There is a steel skid placed at the bottom of the sander and this is the area where the sandpaper contacts the surface being sanded. Most sanders also have a dust port that can be connected to a dust extraction system or household vacuum cleaner.
Using a belt sander
Applying too much pressure will create deep impressions in the wood that can be difficult to remove. Sand with the grain and keep the sander moving at all times to avoid sanding depressions in the wood. Move the sander in a circular motion with the grain. Also, hold the sander by the handles and allow the weight of the sander to do most of the work. Adding too much pressure will also cause belts to wear faster and clog with varnish and paint.
Edges of boards can be sanded with a belt sander. It can be difficult to keep the sander flat against a narrow edge, and if you plan to sand more than one edge, it is better to clamp several boards together. This makes it easier to balance the sander and ensures that all the edges receive the same amount of attention.
The orbital sander has a base plate attached to the body of the sander via rubber grommets. The internal drive delivers power through these grommets causing the base to vibrate. This configuration causes the sander to oscillate creating a gyroscopic movement which moves the sandpaper underneath in a random oval pattern. If you hold an orbital sander against a workpiece and sand very lightly, you will feel how it gravitates towards a different direction each time – something like a pool Kreepy.
In operation the oscillating action will be combined with the vertical or horizontal input from you moving it up and down. It is designed to remove only a small amount of material and is used in the final finishing. This makes orbital sanders more forgiving and easier to perfect.
Using an orbital sander
Applying too much pressure will strain the sander, causing it to bog down. At the same time, the pressure will cause the sander to create shallow swirls on your work surface that undo any progress you may have made. The handles on an orbital sander are mainly for guidance and keeping the sander flat against the work surface. Holding the sander by the handles will allow you to apply even, gentle pressure, maximising the contact area of the abrasive.
When sanding the edges of boards, allow only half of the sanding pad to extend over the edge of the piece being sanded. This will prevent rounding of the edges.
Orbital finishing sanders
Quarter sheet square finishing sanders are relatively quiet, have low vibration and can reach places the larger orbital sander cannot reach. For example, it will be possible to get right into the corner of the surface on the inside of a framed object. It is called a quarter sheet because it uses a quarter of a conventional sheet of sandpaper.
Detail/finishing random orbital sanders are smaller and normally have a shape that allows you to get into difficult spots. They are good for picking out high spots and reaching into crevices. Some of these sanders come with interchangeable accessories in shapes that are designed to help you get into the tightest spots.
Random orbital sanders
Random orbital sanders oscillate, but also rotate the sanding disc at high speed. They have a round sanding pad and will remove more material than an orbital sander, but less than a belt sander, making it the perfect all rounder. The spinning motion added with the random orbital sander means that the path of the paper moving around changes. When trying to flatten an indentation or imperfection, it can be tempting to tilt the sander in an effort to apply concentrated pressure in a particular area.
This will certainly damage the surface and take you back a few steps. These sanders normally have one handle and are operated with one hand, allowing greater manoeuvrability.
How to use an electric sander
• Start with a coarse grit sandpaper and move your way up.
• Allow your strokes to overlap slightly.
• Avoid applying too much pressure – allow the sander to do the work.
• Move the sander parallel to the grain of the wood where possible.
• Always keep the sander flush against the surface.
• You can run a pencil over the surface being sanded. This will allow you to see where the sander is making contact and where more
work must be done.
• As with most power tools, it is important to have the orbital sander running before it makes contact with the work surface and only switched off when it has left the piece.
• It’s easy to become obsessed with the sanding job; giving the tool some rest time every half an hour or so may help to prolong the
life of the sander.
Sanding produces tiny microscopic particles of dust that may not be visible to the eye. This dust can permanently scar your lungs and reduce lung capacity. Many sanders are loud and because they are often used for a long period of time, the possibility of hearing damage is increased. At the same time, it is impossible to know if there are nails or other objects in the wood you are sanding. A sander has the ability to launch an object at speed. Because of these dangers, a dust mask, hearing protection and safety goggles are required.