Construction techniques

Sawing

Drilling

Edge treatments

Chamfers, splays, bevels, mouldings, hollows and grooves

These are known as arris treatments. An arris is a corner where two adjacent sides meet. The arris might get treatment to remove sharpness (like the opening of a letter box) or for decorative purposes (i.e. to match something close by). Chamfers are either continuous or stopped (Fig. 1). They can be small or large but are always 45° and can be produced by simply being sanded, marked with a pencil gauge and planed, or by being spokeshaved or power routed. Splays are created at any angle except 45° , are rarely stopped, are pencil gauged and are normally planed (Fig. 2). Bevels are removed off a complete side rather than just an arris, and can be any angle. They can be produced by marking then planing, or by being cut on a bandsaw or circular saw.

Mouldings are fancy continuous profiles (like architraves or skirting boards) or much smaller ones that are attached as decoration around, for example, a jewellery box lid or storage chest panel. Classic shapes are beads, half-rounds, quad, ovolo, cove, boledictions and ogee, which are produced by power routers or specialist machinery (Fig. 3). Hollows and grooves are used to break up a flat surface and enhance an otherwise boring panel or door. They can be produced with a router or a scratch stock (Fig. 4)

Figure 1. Stopped chamfers with straight and curved stop ends

Figure 2. Chamfer, Splay and Bevel

Figure 3. Moulding types

Figure 4. Hollow and groove made with scratch stock

Figure 5. Router bit set showing common edge treatments and other router functions

Nailing and Screwing

Nailing

Nailing is the simplest form of fastening (Fig. 1) and is mainly used in simple box construction. Screwing makes a stronger join but is harder to conceal than a nail head. Check with a try square that all corners are 90° and that the parts being joined are the same width. Hold one piece of timber in the vice, apply the glue and join the other piece of timber to it. Centre the nails in the thickness of the timber and, for greater holding power, skew them across the width rather than driving them square to the face. This is known as dovetail nailing (Fig. 2) and nailing a centre vertical nail first locates the two pieces of timber. Punch the heads slightly below the surface.

Figure 1. Nailed butt joint

Figure 2. Dovetail nailing

Increase the strength of the join by securing a small piece of wood, square or quadrant in the internal angle (Fig. 3).

Figure 3. Nailed and butt joint with strengthening block

When nailing two flat pieces of timber together, avoid nailing the nails all in line as this may split the wood. Stagger the nail positions by zigzagging them.
As a guide for choosing the correct length when nailing across the grain into the second piece of wood, use nails with a length that is approximately three times the thickness of the top piece. If going into the grain of the lower piece, there is less holding power; therefore, use a nail with a length that is approximately four times the thickness of the top piece.
Use the thinnest nail that will do the job as this reduces the chances of the wood splitting.
Nail punches are made from high carbon steel that has been hardened and tempered. They are available with tip sizes from 0.75 to 8 mm-to suit most nails. They are used to drive nails 2 or 3 mm below the surface of the wood prior to filling it with putty that matches the colour of the wood, thereby hiding the existence of the nail. They are used with hammers with metal heads.
Pincers (Fig. 4) which are generally 150 mm long, are used to extract bent or unwanted nails. By placing a piece of scrap plywood under the curve of the lower jaw then gripping and rolling the jaw down and away from the nail, pincers will easily remove the nail without damaging the surface of the wood. One end of a pincer arm normally has a small claw which may be used to extract certain small nails

Hint: Always use pincers along the grain and away from an edge to prevent unnecessary marking and tearing of the wood

If you are using nails near the end of a board, for example when assembling a corner joint for a box, there is a possibility of splitting the wood up to the end grain. This can be avoided by blunting the tip of the nail so that it acts like a punch rather than a pointed wedge while it is going through the wood. To blunt the tip, turn the nail upside down on a solid metal part of a vice and lightly tap it with a Warrington hammer (don't bend it). Another method to avoid splitting the wood is to pre-drill holes slightly smaller than the nail's diameter, but this is time-consuming.

Figure 4. Pincers for removing nails

Hint: If nails keep bending, it could be due to the angle at which the hammer head hits the nail, the timber might be too hard (use thicker gauge nails instead or pre drill small holes) or the face of the nail head might be too smooth. This can be easily fixed by roughing it up by abrasive paper or rubbing it on concrete.

Screws and their uses

Wood screws are mostly made of mild steel, copper or brass. They consist of the following parts: Head, the shape of which gives the screw its name; Shank (beneath the head), about 2/3rds of which is threaded to a point; Thread, which draws the screw into the timber and gives the screw greater holding power than nails. The heads of most screws are slotted to take the flat tip of the screwdriver. Special types of screws such as Phillips and Pozidriv, which have crossed slots, require their own form of screwdriver.

Mild steel screws are often galvanised (for use in damp positions), nickel plated, blued, japanned, oxidised, etc, to match the fittings they secure.

USES: For securing pieces of timber together, strengthening joints, and fixing metal fittings, such as hinges, catches, locks. to wood. Use brass screws in European oak-steel screws corrode quickly.

Screwing

As a general rule, when choosing the length of a screw it should be approximately three times the thickness of the top piece of material.

Always ensure that a screwdriver fits correctly into the screw slot (Fig. 1) and is not worn (if a flat bladed one is worn it can be reground but the Philips and Pozidrive type must be replaced).
To avoid problems when driving screws into timber, always ensure that the screwdriver is vertical and that your hand and elbow are perfectly in line with it. Always push as you turn-whether tightening or loosening the screw (until it is really loose).
Rubbing a little wax or soap across threads will reduce friction when driving the screws.
When using several slotted screws, as in shelf supports or hinges, it is good practice to head the screws, which means ensuring that all the slots in the screw heads line up and follow the direction of the wood grain.
When mounting a frameless mirror (through holes drilled in the glass), special brass countersunk screws are used that have a small threaded hole in the top. It is important not to over tighten against the glass and then screw on small domed chrome caps to hide the screws.
When using brass screws, which tend to break easily, it is good practice to first use a steel screw of the same size. This creates the thread, which is then ready for the brass screw.

Hint: To use a screwdriver successfully, try to keep your forearm in line with the blade and no matter whether you are tightening or loosening, make a point of pressing down as you turn to prevent the tip from coming out of the slot.

Hint: If the screwdriver is too hard to use and keeps slipping off the screw head, the problem is inevitably the incorrect pre drilling of the holes

Figure 1. Correct fitting of a screwdriver

Sanding

There are a number of steps to careful surface preparation.

If necessary, clean off the surface with a smoothing plane, sharpened super-keen.
Remove plane marks and tears by scraping the entire surface with a hand or cabinet scraper (see below).
If the surface is to be coated with a material likely to raise the grain see 'Raising the grain' .
Sand along the grain (see 'Using abrasives by hand' further down this page).
Fill holes or breaks with stopping (putty) (see 'Preparing for the finish').

There is a step between planing and sanding that is sometimes omitted . This step involves removing plane marks or tears around knots by using a hand or cabinet scraper. Hand or cabinet scrapers are normally rectangular, but curved scrapers are available for special shapes or removing a mark in an isolated spot. The cutting edge of a scraper is a 'burr' along the base that, when flexed, leaned forward and pushed on acts like a mini plane and smoothes the surface . It is not recommended that you use abrasive papers and then return to a scraper as loose grit will blunt the scraper edge. If only dust is produced it means the scraper needs resharpening.

'Sanding ' is the term used to describe the process of cutting wood fibres with abrasives to prepare the surface for a finish. You will often hear sheet abrasive materials loosely referred to as 'sand paper', even though such materials are not generally made of sand.

Modern abrasives

Garnet

The garnet, which is a natural semiprecious stone, reddish brown in colour, is the most widely used wood abrasive. It is of medium hardness and toughness, and, due to its tendency to fracture, it forms new cutting edges as it is used.

Silicon carbide

This shiny, dark grey to black synthetic material is made of coke and sand fused together in an electric furnace and then ground. Due to its brittleness, it fractures into sharp, wedge-shaped slivers. Almost as hard as diamond, it is generally used on wet-or-dry (waterproof) papers and, increasingly, on dry self-lubricating papers (those coated with zinc stearate to prevent clogging).

Aluminium oxide

This is extremely tough and resistant to wear and normally ligh t grey in colour, although other colours are available. It will penetrate almost any surface and is particularly suitable for heavy -duty machine sanding. It is also an electric furnace product, made from bauxite, coke and iron filings.

Glasspaper(sand)

Basically, glasspaper is pale yellow, crushed glass that is glued to stiff brown paper. This type of abrasive is centuries old and is still used for hand sanding.

Backing and bonding materials

Faster cutting by both hand and machine has been mad e possible with the introduction of harder and tougher natural and synthetic abrasives and a variety of backing and bonding materials. Backing materials include paper and cloth (the latter being easy to tear into strips). These backing materials make sanding strips that are useful for curved work. Bonding materials include various combinations of animal glues and resins, to attach the grit to the backing.

Mineral grading

Abrasives are crushed, then sieved through accurately woven silk screens. The mesh of the screen is numbered according to the number of openings per 25 mm and this number is used to designate the grit size of the abrasive. Thus, a 100-grit abrasive would be sieved through a screen having 10000 openings to the 625 mm2 (25 mm x 25 mm). In woodwork, 60-80 grit is considered rough, 100- 120 grit is medium, 180 grit is fine and 240 grit is very fine.

Types of coating

Coated abrasives are of two basic types: closed coat and open coat.

Closed-coat abrasives have no voids or spaces between the grains; the backing is completely covered with grain particles. This type is used for heavy sanding operations, as with power machines.

Open-coat abrasives have the grains spaced at a predetermined distance apart covering 50% to70% of the backing surface. Because this type of coating allows the cuttings to drop free and does not clog the paper, it is especially suitable for use on resinous wood like radiata pine.

Using abrasives by hand

Sanding is a careful, precise operation intended to produce a fine finish.

The sheets, which are sized 280 x 230 mm, are cut into conveniently sized pieces (about six to a sheet), which are used on a soft block of cork, rubber or a soft board glued to a wood block.
For all clear finishes, sanding must be along the grain. Working across the grain leaves tiny scratches, even with fine abrasives, and these will show when the clear finish is applied,
particularly if the work is to be stained. For this reason disc sanders should not be used.
The normal procedure is to use several grades of abrasives, finishing with a fine one.
Care should be taken to keep the surface flat and to avoid rubbing off corners.
For shaped work, a contour block is used to bring all of the abrasive in contact with the wood.
Sanding sticks, abrasive paper files or strips of emery cloth are most useful for intricate and rounded shapes.
Small items are best sanded by rubbing them on a sheet of abrasive placed on a smooth, flat surface.
Individual parts, especially their inside surfaces, are always sanded before assembly and given a final touch up later.
For painted finishes, sanding is sometimes completed across the grain so the paint will fill the grain.
Do not exert undue pressure on the block because this exerts excessive wear on the abrasive and tends to cause scratching, even working with the grain. Dust off the work frequently with a soft brush and knock the abrasive against your hand occasionally to free the dust.

Sanding machines

There are four types of sanding machines for hand use: disc, orbital, belt and drum sanders. The disc type of sander does not produce a satisfactory finish because of its circular action, but is useful for shaping and reducing surfaces quickly. Orbital sanders produce a good finish . Disc and orbital sanders are also available as drill attachments, while drum sanders are easily made with a spindle for use in a drill. Drum sanders may also be used between the centres in a lathe.

In industrial environments, where sanding is a highly developed finishing process, single and multiple drum, belt and disc type sanders are used in specially made machines capable of sanding over one metre in width (see section on machines).

Hint: If there is an accidental bruise (dent) in a project, possibly due to lack of care in storage, most of it can be restored by steam ironing. Dampen some clean cloth or paper towel (not dripping) place it over the bruise and press a hot iron over it until the paper towel/cloth is dry. Remember to keep the iron still. Repeat this process two or three times, if necessary, and allow the area to dry before re-sanding the raised grain.

Scraping

Cabinet and hand scrapers

Generally made of carbon steel and available in various curved (convex and concave) or rectangular shapes, the scraper uses thicknesses that vary from 0.4 mm for very fine work to 1.5 mm for heavy-duty work. The cutting action results from a burr formed on the edge of the scraper that acts like a mini plane. Cabinet scrapers are held in a cast-iron frame, are made adjustable and ground to 45° before producing the burr. The hand scraper is ground to 90°; the burr is produced and is then used by hand. They work very well, when sharpened correctly, and can produce a fine surface that needs very little sanding

Magnified view of the effect of the hand scraper

How to use a cabinet scraper

Push the scraper at a skewed angle when starting near an end and change the angle with each stroke

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