Sanding: Art by Nature, Perfect by Design

Wood is not as resistant to time, or to scratches, as metal or stone – but this is what makes it so special! Each piece of wood has a unique grain pattern, and wooden furniture or floors can be given different textures and colours over the years. The quality of sanding of solid wood and wood-based panels is what makes the difference between standout work pieces and the also-rans. Check out why…

Sanding of wood can be done manually (L) or with the latest robotic sanding machine, such as this one from Biesse (R).

Sanding is the process of levelling and smoothing the wood surface, by making the top layer uniform. It is, therefore, vital before polishing, painting or impregnating, because wood protection and decoration products work much better on well-sanded wood surfaces.

Unfortunately, sanding is generally low on the priority list among furniture and panel manufacturers. Sanding is viewed as an obstacle, but it is the opposite: sanding is finishing. One must treat it as a separate – and integral – first part of the finishing process. The quality of a sanding job can be the difference between a masterpiece and a large paperweight!

But why do we sand wood anyway? Hard-to-reach areas generally retain saw marks; glue joints are not flush with the components; open areas are prone to chatter marks from the planer; and hand-made work pieces leave much to be desired in smoothening out surfaces, joints and curves.

Sanding also gets rid of old paint, coating or adhesives, and scratches on wooden surfaces. It is essential to sand wood before using veneer. Even when gluing wooden elements together, sanding the area of contact is necessary to ensure correct fit and uniform application of adhesives.

Manual Vs machine

Sanding can be accomplished manually or by machines. Manual sanding is good if the work piece to sand is very soft or soft wood. Manual sanding involves the use of sandpaper with application by hand. The sandpaper can be attached to a holder to enable sanding of larger surfaces of wood.

A wood sanding tool – usually powered by electricity or air under pressure (pneumatic) – can speed up the process of smoothing and levelling surfaces significantly. A sanding tool can also help achieve a more even wood grain structure.

While manual sanding is best done by hand in furniture with angles and curves, sanding machines are better suited for large-flat surfaces, such as a table or the sides of a wardrobe.

Sanding larger pieces of wooden furniture by hand can be both tough and time-consuming. Manual sanding is better for angles and curves, as well as all kinds of decorative elements.

Whether sanding by hand or with a sander, the appropriate sandpaper is required; and the full process of sanding will require several types of paper with different grain sizes. 

The grain size literally means how big the grains on the sandpaper are – the smaller the number, the bigger the grains.

The most common sandpaper grain sizes are coarse grain (40-60), average grain (80-120), fine grain (150-180), very fine grain (220-240), and super-fine grain (above 280).

Sanding wood begins by sanding harder and more aggressively, then moving on to more delicate smoothing and refining of the wood surface. In other words, one should progressively go from coarser (low number) to finer (higher number) sandpaper.

When sanding untreated wood, it is a good idea to start with a grain size of 80-100, to remove the largest cavities and bumps. Large grains are also useful when removing old paint, varnish or glue from a piece of furniture or wooden item.

The final sanding work should be done with sandpaper with a grain size of 180-220. One should use finer sandpaper for polishing, when working on wood that has already been treated.

Even after sanding, wood should have some texture and should not be perfectly smooth. Otherwise, it may be too hard to treat or paint. Varnish or paint may not stick to the surface well enough, and could start to peel off after some time.

If the surface has to be darker after being treated, one needs to use thicker paper. The smaller the grain (the bigger the number), the brighter the wood will appear later on.

The choice of suitable grain size of the sandpaper also depends on how hard the wood is. The more resistant a given material is to normal wear, the more coarse-grained paper is to be used.

When sanding hard wood such as oak, one can start with a grain size of 120, then go to 150, and finish off with 180. But in the case of linden, spruce or walnut, one can use sandpaper with grain sizes of 150, 180 and 220 respectively.

Wood sanders

An angle grinder is a tool for both cutting and cleaning various kinds of material. It can also be used for sanding. To use it on wood, the operator will need a sanding disc to which is attached a sanding pad. However, improper handling of an angle grinder with a flap disc may result in damaging or even burning the wood.

A sanding disc, with which one can use various grain sizes, is a better option. The grain size classification is the same as with sandpaper. Sanding discs are therefore easier to use and more practical than a flap disc.

Disc sanders are usually stationary devices, with a vertically mounted disc and an adjustable base for the work piece that needs sanding. One can use them for jobs requiring a high level of precision. They are often recommended for quick work with smaller wooden elements.

Orbital sanders usually have a rectangular or triangular disc for wood. They are great for both larger flat surfaces and places that are more difficult to reach. They are especially recommended for sanding soft wood.

Random orbital sanders are a more sophisticated version of orbital sanders. During use, the angle of rotation of a random orbital sander is variable. They are also often more powerful than orbital sanders, making them more suitable for processing harder wood or removing old paint.

Belt sanders are especially handy for sanding very large wooden surfaces, such as floors or panelling. Using one properly may require more practice than other sanders, but they let you work much faster on harder material.

Stationary brush sanders can effectively and consistently sand sealer on profiles, such as mouldings, raised panel doors and drawer fronts. The bristles of brush sanders can conform to profiles, effectively sanding at various thicknesses without destroying the profile.

Many types of brush heads and grits are available; and quality brush sanders offer machine adjustments to handle a wide variety of materials and finishes.

Finishing wood

Machinery and abrasives are now matched more precisely to a specific process. The change in coatings alone has sparked the need for more advanced and process-specific brush sanders. However, some basics remain basic to the process and art of sanding.

Before sanding, the surface to be sanded must be cleaned, taking care that the work piece does not become too moist. A vacuum cleaner or a brush nearby can get rid of the dust from the sanded area.

Start with a coarser grain first, then a medium one, and finish with a fine grain.

Keep cleaning the sanded wood as one goes along, otherwise particles could stick to the work piece and risk scratching the surface. Fine details can be finished with a special sanding sponge, making it easier to distribute the pressure evenly and sand areas more difficult to reach.

Wood fibres are basically torn apart during sanding, so it is very important to sand along the grain. If wood is sanded against the grain, the fibres get damaged, leaving the surface rough, scratched and uneven. Even oil or paint applied later on will not solve the problem!

The last stage of sanding is protecting the surface, or imparting a specific colour. Impregnation protects the wood against UV radiation or moisture. It can be enriched with pigments that will give the wood a deeper colour, while leaving the grains and rings clearly visible.

Applying varnish – translucent or transparent – after impregnation creates a protective layer against scratches and mechanical damage. More traditional methods, such as waxing or oiling, can also be employed.

Common mistakes

The sanding stage is usually the worst place that a work piece can be damaged. Machine components and abrasive belts and pads wear unevenly and create problems and unnecessary expense.

Finish, accuracy and the machine all suffer if this is not part of a regular maintenance schedule. A machine that is calibrated and maintained correctly helps production in the short and long terms.

Most productivity issues from sanders, regardless of type, can be summed up in two words: service and training. The vast majority of sander problems stem from a lack of one, or both.

This is where operator training comes in. The ability to recognise sanding defects, and know which components on the machine to start trouble-shooting, is invaluable.

The basic task for any woodworker is to check accuracy and calibration of the sanding machine. One way to do it is to sand three consistent work pieces – two at the edges of the conveyor belt and one in the centre.

After sanding at a low feed speed, so the belt has time to cut, measure the sanded parts, compare dimensions and adjust the machine settings accordingly.

The purpose of pre-finish sanding is to give the work piece an even, clean look that is free of visible scratches. In a majority of cases, wooden pieces only need medium-grit sandpaper to create that optimal look.

Over-sanding is a frequent mistake made by woodworkers. It must be remembered that any small imperfections can be smoothed out when sanding between coats of finish.

Remember that employing the wrong belt or pads, or the wrong abrasives on them, can damage your machines, belts/ pads – and one’s expectations from the sanding process!

What separates a good craftsman from a great one is their ability to repair these inevitable mistakes. And, ultimately, it is impossible to produce a smooth and professional finish on wood without the help of high-quality sanding paper and sanding machinery.

 

Sanding abrasives come in the form of belts, discs and bands, and in different shapes and sizes.

 

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