Sanders and Abrasives

It is not known when sandpaper (later more properly called "glasspaper"), was introduced. The earliest known reference is to an advertisement in the Boston Gazette of September 1764 for sand and emery paper, but it was not in general use until about 1800. The date given for carborundum in the Oxford English Dictionary is 1893; this material and other abrasives were widely adopted for machine sanders and grinding wheels at the beginning of the present century.

Modern abrasives are available in a variety of finishes. They can be used by hand or fitted in power tools to sand individual workpieces, large floor surfaces or small local areas.

The first abrasive used by woodworkers and masons was probably sand itself. An early Egyptian relief at Saqqara shows two workmen apparently rubbing down a tabletop with small blocks of stone: they would have had little difficulty in finding plenty of sand to use with them. In the Middle Ages the skin of the dogfish was used for this purpose. At Westminster, London in 1350 a "hundysfyshskin for the carpenters" was bought for the equivalent of a dime. This was still in use as late as 1708, when the inventory of Charles Phimhley, a cabinetmaker of Philadelphia, listed: "4 pairs of fish Skins at 10-". A few years earlier Moxon advised finishing work with "Seal-skin or Dutch reeds".

Abrasives are available to finish a wide range of materials. There are three categories of abrasive, coarse, medium and fine, but within each grade there are progressively finer subdivisions. Apart from the size of the grain the spacing of the grain is also graded. The closely packed grains, or "closed coat" abrasives, will cut quickly but clog easily. Wide spaced or "open coat" grains are best suited for materials like paint which tend to clog abrasives quickly. Sandpaper is no longer available although the word is still used as a general term to describe all abrasive papers.

FLINT OR GLASSPAPER

This is most often confused with sandpaper because of the yellow color of the adhesive and backing paper. It is the cheapest abrasive available, wears quickly and is used to roughly finish lumber. For a finer finish, choose a better quality grit.

GARNET

This is a natural red material, which; backed with paper, is used to hand finish all types of lumber including hardwood. It is harder than flint and is available in finer grades. Use it dry.

EMERY

Another natural material, this is used mainly to finish metal. It is available with paper or cloth backing. Paper backing is adequate for flat areas, but a cloth backing is much stronger especially if you are working on tightly curved sections. It can be lubricated with water.

SYNTHETIC SILICON CARBIDE

This is harder than emery and is backed by waterproof paper so that it can be used wet or dry to finish paint or metal. (It is sometimes known as "wet and dry" paper.) When rubbing down paintwork, the water and paint particles form a slurry which should be wiped off the workpiece while still wet. The abrasive itself should be rinsed periodically in water to remove any paint which is clogging the grit. Silicon carbide can also be used on bare wood, but should only be used dry.

ALUMINUM OXIDE

Another synthetic material with paper and cloth backing which is often used to machine-sand lumber, plastics and metal.

TUNGSTEN CARBIDE

This is the hardest abrasive material. It is mainly used in sanding machines, and is therefore sold in thin metal disks or strips.

Sanding round stock

Mount the work on a vise and pull cloth-belted emery strips across the surface. Angle your strokes to cover all the pipe.

Sanding Block

SIZE: Various.

MATERIALS: Block: cork, plastic, rubber, softwood; Covering: abrasive paper

USE: To finish flat surfaces

Abasive papers used on their own will oftn produce uneven sanding and are likely to follow any undulations in the workpiece. Paper wrapped around a sanding block will keep a wider area of abrasive flat on the
workpiece.

A quarter of a standard sheet of abrasive paper is ideal for wapping around a sanding block. Tear the paper rather than cutting it with a knife or or of scissors.

The simplest block is merely a rectangular piece of cork, rubber or softwood. Other, more sophisticated blocks are moulded to fit the palm of the hand and take strips or even rolls of paper ready cut to size.

Sand wood in the direction of the grain. Scratches across the grain, which may not even show when the wood is un-finished, will be exaggerated by the application of varnish or polyurerathane paint.

Clogged abrasive will not cut efficiently. Remove the paper From the block and tap it firmly on the bench to remove dust. Wash clogged material from wet and dry paper.

Shop bought blocks

These are shaped to the hand and supplied with abrasive paper cut to size.

Tearing abrasive paper

Fold the sheet in half over the edge of a bench. Hold one half firmly on the bench and pull down the edge to tear off the other half.

Sanding edges

Keep the block flat on the work so that it will not round off the edge where it overshoots.

Belt Sander

SIZE: Belt: 3 and 4in.; Capacity 1.150 to 1,600 surface ft. per minute

MATERIALS: Various

ACCESSORIES: Abrasive belts dust collecting bag

USE: To sand wood and metal quickly

The belt sander is a powerful machine which will remove a considerable amount of material, especially if a coarse abrasive paper is fitted. It can be used to finish lumber or metal and will also remove old paint or varnish.

The abrasive belt is a continuous band which is driven over two rollers to produce a non-stop sanding action. The rear roller is powered, while the front roller is adjustable for tension and tracking of the belt. A pad, known as the "platen", is mounted between the rollers and holds die belt flat on the work. If possible, choose a sander which is already fitted with an extractor and dust collecting bag.

Using a belt sander

Hold the machine in both hands and switch on before applying the belt to the work. Gently lower the sander on to the work. Once in contact keep it moving to avoid it scarring one area. Pressure is not normally necessary, but this depends on how much material you wish to remove and how quickly you want to do it.

Move the machine in a series of forward and backward strokes gradually traversing the workpiece, overlapping section by section. Lift the tool off the work before switching off.

Sand wood with the grain to produce the best finish. Sand at an angle to the grain to remove material quickly or to level a surface. Re-sand parallel to the grain and with a finer grade of abrasive to remove the cross grain scratches.

Sanding edges

Keep the machine flat when overrunning the edge of the work to avoid rounding off.

Changing a belt

Before fitting the belt, disconnect the machine from the electrical supply. To slacken a belt, reduce the distance between the rollers by operating a lever or by resting the tool on its front roller and applying pressure. This pushes the roller back against a spring and locks it in the retracted position.

Taking up tension

Following the feed direction arrow printed on the inside of the belt, align the belt and release the front roller to take up the tension.

Tracking

The tracking of the belt can be adjusted on all machines. If the belt is not running true or parallel with the body of the machine, it may move sideways, damaging its edge. It may even run off the machine. Adjust the angle of the front roller if necessary, by switching the machine on and off momentarily between adjustments. Make final adjustments with the machine running.

Once the new belt is fitted adjust it with the tracking adjustment knob on the side of the machine.

Disk Sander

SIZE: Diameter: 4 to 9in.

MATERIAL: Rubber, aluminum, zinc

USE: To sand wood, metal and plastics

There are several models of disk sander, but they all operate in the same way. A round disk is applied to a pad which is driven in a circular motion. This produces cross grain scratches, so disk sanders are only suitable for reducing the surface or cleaning off old finishes. The simplest form of disk sander is fitted to a power drill. One pad is made of rubber, and has either a plain shank projecting from the centre, which fits into the drill chuck, or a threaded shaft which screws directly into the drill spindle.

Solid metal disks, faced with rubber, have a shank fitted to the centre with a ball joint. This enables the disk to remain flat on the work even when the drill is held at an angle. The rubber disk, on the other hand, relies on flexing to perform efficiently. Used this way the disk is more stable and consequently less likely to leave swirl marks. When using the sander keep all disks moving and apply light pressure only.

Fitting a disk

Fit the abrasive disk to the rubber pad with a screw and a shaped washer.

Using a rubber disk

Angle the drill, flexing the top section of the rubber disk.

Abrasive disks

Abrasive disks are either made from abrasive material bonded to a paper backing or from pressed metal with tungsten carbide grains bonded to die surface. They are fitted to the backing disk with a screw thread and shaped washer which screw into the centre of the backing pad. Both washer and screw head are recessed below the working surface.

Offset sander grinder

Offset sander grinders are fitted with 7 and 9in. abrasive disks. These are industrial machines which may be worth renting for heavy duty work.

Bench mounted Sanders

These can be very useful for shaping work. A small scale unit can be set up using a portable electric drill in a horizontal drill stand fitted with a worktable and flat metal disk.

Gluing on disks

Hold a stick of adhesive on the surface of the metal disk while the machine is running. When the adhesive has melted and the disk surface is coated evenly, disconnect the machine and press a paperbacked abrasive disk centrally onto the backing plate of the disk.

Using the sanding table

Check that the sanding table is square to the face of the disk with a try square before use. A mitre gauge runs in a groove across the table which can be set to trim ends square or at an angle. Hold the work against the downside of the disk to keep it on the table. Keep it moving to avoid uneven wear on the disk. Too much pressure is likely to burn the work.

Foam Drum Sander

SIZE: Diameter; 5in.; Width: 2in.

MATERIAL: Arbor: steel; Drum: particle foam

ACCESSORIES: Abrasive belt

USE: To sand flat and curved surfaces

The drum is fitted with a steel arbor or shaft, which fits into the chuck of an electric drill. A continuous belt of abrasive material is slipped onto the resilient foam drum, which can shape itself to accommodate the contours of the workpiece.

Using the drum

Use the foam drum sander to finish concave and convex shapes conveniently, as well as standard flat surfaces.

Finishing Sander

OTHER NAMES: Orbital sander, pad sander

SIZE: 4 x 4in., 4-1/2 x 11in.; 4,000 to 14,000 orbits per minute

MATERIAL: Various

ACCESSORIES: Abrasive strips

USE: To sand a surface finally

 

The finishing sander achieves a fine smooth surface on wood by a series of tiny, high speed, orbital cuts. Some machines can be switched to an "in-line" movement for the final finish. A wide variety of sanders exist for one and two handed use as well as an attachment for an electric drill.

The finishing sander takes ready cut abrasive paper strips, which are stretched across a pad which holds them flat on the work. When using the sander work in bands parallel to the grain with the machine held at a slight angle to the direction in which it is moving. Finally finish with the machine held parallel to the grain and if possible, switched to in-line movement, while constantly moving the machine up and down the workpiece.

Fitting abrasive paper

Attach one end of the strip under a spring clip or toothed roller. Stretch the paper and fit the other end the same way.

Using the sander

Work parallel to the grain, holding the machine at a slight angle to the direction of its travel. As you cover the work area, slightly overlap each sanded band as you go.

Floor Sander

SIZE: Drum diameter: 8 and 12in.; Disk diameter: 8in.

MATERIAL: Various

ACCESSORIES: Abrasive paper, dust collecting bag

USE: To sand wooden floors for refinishing

Two types of sanding machine are available from rental companies. The larger drum sander is used for the main floor area while a smaller disk sander will clean up the edges against the baseboard or areas such as hallways and landings, which are too small for the big machine. There are even types which will fit beneath radiators.

Both machines produce a considerable amount of dust. Even though they are designed to suck the dust directly into collecting bags, it is advisable to wear a face mask and if possible; seal off gaps leading to odier areas of the house.

Fitting new paper to drum sanders

Floor sanders are supplied with abrasive paper in coarse, medium and 4ne grades. The coarse paper is used to level the surface; medium and fine are for finishing.

1. Disconnect the machine from the electrical supply. Lay the sander on its back and push back the guard. Remove the worn paper by loosening a clamp with the tools provided by the renting firm. (The drum itself may be split lengthwise on some models).

2. Insert one end of the new paper under the clamp, wrap it around the rubber roller and insert the other end.

3. Make sure paper is lightly wrapped around roller and tighten clamp. Replace guard.

Fitting new paper to disk sanders

Coarse, medium and fine abrasive paper is also supplied for disk sanders. Disconnect the machine from the electricity supply before fitting new disks or paper. Turn the machine upside down to fit new disks.

1. Undo the retaining clamp by turning it counter clockwise in the middle of the disk.

2. Remove the old disk and throw it away. Fit a new one of the appropriate coarseness and tighten the clamp once more. Turn the sander upright.

Preparing the surface for sanding

Remove all carpet tacks, edging strips or adhesive tape from the surface. Sink all nail heads. If the gaps between the floorboards are very large, consider lifting them and closing them up before sanding.

Sweep the floor to remove loose material which might damage the machine's roller.

Sink all nail heads heads the surface of the boards with a hammer and nail set.

Filling wide gaps

Make a steel scraping tool, tapered to rake out the gaps between the floorboards. Either fill the gaps with papier mache and sand it flush when it is dry, or tap in suitably tapered strips of softwood and plane them flush when in place.

Using the machines

Never switch on the drum sander while it is resting on the floor. It will either move off on its own or sand a deep mark in the floor. Tilt the machine backward to lift the roller off the floor, switch on the machine and gradually lower it.

At the end of the run, tilt the machine once more, turn it around, and sand the section parallel with and overlapping the previously sanded area.

If the boards are already flat and only require cleaning, you need only sand the floor parallel with the boards.

1. Lower the sander. As it comes into contact with the surface, start to move the machine across the floor at an angle to the beards.

2. When the entire floor has been covered, sand at an opposite angle to the first. 'I his will level any high points instead of following them.

3. Fit a medium then a fine paper to finish sanding the floor in the direction of the boards.

Finishing off

The floor sander will not be able to clean the edges of the floor near the baseboard or get into any small or awkward corner areas. When you have done all you can with the big machine, switch to the smaller disk sander.

Vacuum the whole area to remove all loose dust before applying the chosen finish.

Sanding edges

Drape the cable over your shoulder to keep it away from the disks. Grip the handles and switch on the machine. Keep it moving to prevent over-sanding in one area. Take it as far into the edges as the sander housing will allow.

Sanding corners

To clean up corners, use a sanding disk in a power drill. The flexible disk should reach most corners. For even more inaccessible areas, use a scraper and sanding block.