Power sanding

Sanding is an essential preliminary to painting or varnishing most surfaces and although it is quite possible to sand by hand, this is often a laborious and time-consuming activity; and even after a great deal of hard work, you cannot always guarantee a good finish.

Using a power sander makes the job very much quicker and easier, and it has an added advantage in that it allows you to undertake jobs that would be almost impossible to complete by hand-such as sanding floorboards or removing heavy rust deposits from gutters downpipes, and other metalwork items.

Preparatory considerations

Almost all materials-wood, plastic, masonry or metal-can be power sanded providing you choose the correct machine. But both the surfaces and the surrounding areas must be prepared thoroughly before you start.

All nails or sharp objects which might tear the abrasive material or damage the machine must be removed-especially if you are working with wood. So go over the workpiece first to check for these, and keep an eye open for them while you are working.

Even if your sander is fitted with a dust bag there is bound to be some mess, so try to keep it to a minimum-particularly if you are tackling large areas. Moveable furnishings should be taken into another room and all fittings covered with dust-sheets or rolls of plastic sheeting.

Safety and health considerations are also important. Remember that you are dealing with machinery which can either be enormously helpful or potentially dangerous according to how it is used.

Safety goggles should always be worn in enclosed areas or when working with metal or masonry. If the machine is noisy or you are using it for a long period, it is a good idea to wear protective ear muffs at all times.

Types of abrasive

The effectiveness of any sanding machine and the results that you achieve are directly related to the quality of the abrasives employed. Even very good machines cannot work to their full potential if they are fitted with the wrong type of abrasive.

Although ordinary glasspaper can be used, it tends to wear out quickly and become clogged after only a short period of time. Try to find aluminium oxide or silicon carbide paper which is a lot more expensive but will last much longer and sand more effectively. The types with the grit spaced wide apart are best as they are less likely to clog when used at high operating speeds.

Abrasive paper is usually graded both by type and number-fine (100 to 120), medium (80 to 100) and coarse (50 to 60). In addition to these three basic grades there are a large number of intermediate abrasives available as well as extra coarse and extra fine grades.

Self-adhesive abrasive paper is now coming on to the market—types are available for use with disc or orbital sanders. To use these, you must also have a special plastic backing plate which the abrasive sheet is stuck to. The papers can be peeled off and re-stuck on to the backing plate a number of times.

As well as paper and cloth-backed abrasives, rigid metal discs can be used as attachments to power drills. These consist of a light alloy disc impregnated with tungsten carbide grains which are exceptionally tough and do not clog easily.

Attachments for drills

The most basic type of power sanding equipment consists of various attachments which can be fitted to your existing power drill. These allow you to tackle most simple sanding jobs without the need to buy or hire expensive sanding equipment.

Sanding attachments can be fitted ready for use in a matter of seconds. A shaft mounted on the back of the attachment is slotted into the jaws of the chuck-rather like a drill bit. The chuck is then fully tightened with a chuck key until the attachment is firmly held. Sanding discs: These are flat, circular discs of abrasive material mounted at right-angles to the chuck. They are usually used for fine sanding of wood or masonry. When the drill is running, the disc rotates to give a simple,.circular sanding action.

Two types of sanding disc are used. The more common of the two consists of rounded pieces of ordinary abrasive paper fixed to a flexible rubber backing : disc about 125mm in diameter. The paper is held in place by a central screw and wide flange mounted on the front of the backing disc.

Purpose made abrasive discs are available in a number of different grades from most hardware stores. But you can easily make your own from ordinary sheets of good quality glasspaper.

Try to choose abrasives with a strong paper or cloth backing since these will tear less easily during use. Place each sheet on a flat surface, abrasive side down, and use a felt marker to draw a circle around the outside of the backing disc. The paper can then be cut into discs with sharp scissors or a scalpel. Cut a slot in the middle so that the disc can be secured to the backing. Try to make up a number of discs of different grades-ranging from very fine to extra coarse-so that you can work on a variety of different materials.

The second type of disc is made from light alloy and may be rigid enough to be used without a backing pad. Like the ordinary paper discs, these are available in a number of different grades from fine to coarse. They are usually used for rapid stripping of materials which are encrusted with thick coats of paint or covered with rust.

Wear safety glasses or goggles when working with rigid abrasive discs-especially when stripping old paint or rust or smoothing down rough masonry.

Before working with an abrasive disc make sure that it is firmly held in the chuck; a number of unnecessary accidents are caused by discs spinning free during use. Choose a high speed setting, then pick the drill up and hold it firmly by the handle before switching on the motor.

Never hold the disc flat on to the workpiece; it will only dig into the surface and remove too much material. Instead, keep it at an angle of about 30° so that only part of the disc actually touches the surface. Keep the disc on the move all the time, working it slowly backwards and forwards so that only a thin skim of surface material is removed.

Sanding discs should be used with care-especially on softwood-since they often leave circular ‘swirl’ marks which are difficult to remove. To avoid this, start off with a fairly coarse paper disc and then work your way down through a number of medium grades, finally finishing off with a very fine disc. If any swirl marks then remain they can be removed by hand-with a fine piece of abrasive paper rubbed along the grain-or with an orbital sander.

Drum sanders: These consist of a sturdy foam cylinder with a belt of abrasive paper wrapped around it. Fresh belts are easily fitted and are available in a number of different grades.

Drum sanders are no good for very large flat areas, nor can they reach into tight corners. But they are ideal for fine sanding of all materials-particularly wood-since they leave few swirl marks and can be used along the grain. You can also use one to tackle gentle curves-a task that is practically impossible with any other type of sander.

Before starting work make sure that the belt is fitted correctly. It should be tight against the backing so that none of the foam is exposed. Most belts are seamless but others, with joins exposed, should be fitted the right way round so that the join does not catch or snag while the machine is in use.

Use the foam base to press the sanding belt gently against the surface of the workpiece during use. Occasionally withdraw the machine from the work-piece and allow it to speed up again before restarting work. Try to keep the drum on the move all the time and keep a constant check on the belt to ensure that it does not slip to one side.

Flap wheels: These allow you to sand internal corners and sharp curves which are almost impossible with either sanding discs or drum sanders. They consist of a large number of abrasive cloth strips attached radially to a central hub. As the tool is used, the outside edges of the cloth leaves wear away exposing fresh abrasive surfaces. A large number of wheels is available, each with a different diameter and grade of grit from fine to coarse.

Never apply excessive force or pressure when using the flap wheel. Advance it slowly towards the workpiece until just the outer edge of each leaf is brushing against the surface. As each part is sanded, withdraw the wheel and work from a slightly different angle until the whole area has been covered.

Orbital sanders

As their name implies, these work with an orbital-or oscillating-movement so they can be used equally well with or across the grain. They are designed specifically for fine-sanding large flat areas before they are painted or lacquered and should never be used for rapid removal of material; a disc sander will do this far more effectively.

Orbital sanders can be bought as attachments to your existing power drill or as integrals with their own in-built motor. For the majority of jobs around the home there is little to choose between either of these options in terms of performance-although you may be discouraged from buying an attachment because of the time taken to secure it to a hand-held electric drill.

Orbital sanders are sold in two basic sizes-half sheet and one third sheet-describing the size of abrasive paper that can be fitted. A half sheet machine takes paper 115mm x 280mm (equal to a standard sheet of abrasive paper cut in half lengthways), while the one third sander takes paper 93mm x 230mm.

Specially sized sanding sheets are available in a variety of grades although you can easily make your own from good quality abrasive paper. The sheets should be the same width as the rubber pad mounted on the bottom of the machine but must be cut about 300mm longer to allow for fixing.

Some models do have two handles, one mounted on each side of the main motor. Near the top of the machine usually on the underside of the handle is the on/off switch and switch lock control button.

The working end of the sander consists of a flat block mounted about 100mm below the handle. Below this is a rubber pad to which the abrasive paper is attached with either tightening screws or two adjustable clips. The only visible moving part of the machine is the rubber pad which oscillates at speed once the motor is switched on.

It is of vital importance to ensure that the abrasive sheet is secured correctly before starting work. Poorly fitted sheets quickly work their way loose or tear along the edges, causing damage to the rubber pad underneath. Make sure that the sheet is held as tightly as possible and that no part of the rubber pad is visible-especially along both outer edges.

Always switch on the machine before lowering it on to the workpiece. Hold the machine flat against the surface and work it slowly backwards and forwards in broad sweeps. Resist the temptation to press down too heavily: although this removes material faster, the abrasive paper will quickly become clogged and need to be replaced.

Stop the machine occasionally and check the state of the abrasive sheet. If it shows signs of wear and tear or is becoming clogged, replace it immediately with a fresh sheet. If a worn sheet is left on too long the sander will leave small swirls which are difficult to remove except by further sanding.

It is a good idea to start off with an abrasive sheet which is fairly coarse and work down to a fine abrasive sheet as the work progresses.

Belt sanders

A belt sander is a heavy machine that is intended for rougher work-such as stripping paintwork or levelling boards. It gets its name from the continuous belt or loop of abrasive paper which passes around two large wheels, one at the front of the machine, the other at the back.

Most belt sanders are large, heavy machines and it is more likely that you will hire one for special jobs rather than buy your own. However, there are a number of smaller models designed for domestic use.

If you want to buy a belt sander, look for one that is easy to use and control. Some have short handles fixed directly to the body of the machine, others have longer handles so that they can be used while the operator stands up.

It is essential to choose a model which is fitted with a dust bag. This is fixed behind the main body of the machine and collects dust, paint and other loose material from the surface that is being sanded.

Some models have a flat top so that the whole machine can be turned upside down and used as a bench-mounted sander. This can be a very useful device for rounding edges or for sanding small pieces of wood.

It has a handle attached to the main body of the machine where the on/off switch and switch lock are situated. A smaller, rounded handle is fixed to the front of the sander so that it can be controlled more easily with two hands.

The sander has two rollers which carry the loop of abrasive. The front roller keeps the paper in line while the back roller provides drive from the motor mounted directly above it. On the side of the machine is a knob which adjusts the angle of the front roller to stop the belt wandering during use.

Abrasive belts are fairly easy to fit. Turn the machine over or support it at an angle on one of its bottom edges. Then release the tension lever between the rollers and push the two drive wheels together. Any old or worn belts can then be removed and a new one slipped into position over the rollers. Once the tension lever is retightened and the tracking knob adjusted so the belt runs smoothly and absolutely straight, the sander is ready for use.

Belt sanders are far more difficult to control than almost any other type of sanding machine and should be treated at all times with extreme caution. If your sander is of the smaller, domestic variety, pick it up and start the motor before lowering it carefully on to the surface; larger machines should be tilted on their back end before they are switched on.

Once the machine is in position, concentrate on keeping it in a straight line and on covering the whole area to be sanded. There is no need to press down on the sander-its own weight should be enough to keep it operating effectively. Switch off occasionally and check the condition of the abrasive belt. The dust bag can also be emptied at this stage if it is more than half full.

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