Screws And Nails

Screws are used widely in furniture-making and joinery, while nails are the most basic fixings of all, used mostly for carpentry and construction. Screws are stronger and take longer to fit, usually drilling clearance holes first. With nails, you simply hammer them in, punching them below the surface to conceal them.

Screws

Screws for wood vary greatly in pattern, size, quality and purpose. Their appearance may not be important in many situations, but invariably for furniture- or cabinet-making they should enhance the finished piece. Solid brass screws are commonly used for furniture fittings. Screw heads can become damaged easily by using the wrong tool, so always use the correct type and size of screwdriver. A traditional wood screw has a single slot in the head and is countersunk, allowing you to insert it into wood so that it sits flush with the surface. More recent patterns have a cross-headed slot, which offers a better grip when driving or unscrewing them. Most common are Pozidriv screws, similar to the earlier Phillips pattern, but with added shallow grooves between the slots. Newer patterns include T-star and square-headed screws, which require special screwdriver blades to drive them. Hex screws are frequently used in the assembly of woodworking machines and are tightened with a special key.

Threads are designed for driving and fixing screws into various materials. Traditional wood screws have tapered shanks and fit tightly through clearance into pilot holes. Modern screws have parallel shanks, for driving into wood, often without pilot holes. These are less likely to split the wood and are ideal for use with cordless drill/drivers. Screws for MDF have coarse, single threads on their shanks and twin-threaded sharp points for starting. By comparison, chipboard screws have shallower threads. For exterior use, screws should be zinc plated or treated to prevent corrosion (passivated).

TIP

  • When inserting a screw into hardwood for the first time, dip the thread into wax or grease to make it easier to drive home.

SCREW GAUGES

Screw gauge refers to the shank size, although these are not precise diameters. Screws are available in both metric and imperial gauges, with each requiring a clearance hole for the shank and a pilot hole for the tip. Generally, you should select a screw size that is three times the thickness of the smallest piece of timber it has to pass through. Hardwoods tend to need bigger clearance holes than softwoods. Note that metric/imperial conversions are approximate

 Metric Imperal Pilot Hole Clearance Hole
3.0 No. 4/5 1.5 mm (1/16 in) 2.5 mm (7/64 in)
3.5 No. 6 2.0 mm (3/32 in) 3.5 mm (5/32 in)
4.0 No. 8 2.5 mm (7/64 in) 4.5 mm (11/64 in)
4.5 No. 9 3.0 mm (1/8 in) 5 mm (3/16 in)
5.0 No. 10 3.5 mm (5/32 in) 5.5 mm (13/64 in)
6.0 No. 12/14 3.5 mm (5/32 in) 6.0 mm (1/4 in)

Nails

Nails are often used in the workshop when building jigs or temporary structures. A selection of round-head, lost-head and oval nails is useful. When selecting a size, choose one that is three times the thickness of the smallest piece of timber. Panel pins are frequently used in carpentry and joinery work when fixing battens and other small mouldings while glue cures. They are available in a brass finish as well as steel. Smaller veneer pins are suitable for applying fine decorative mouldings to furniture.

Word Discription :

Counterbore The process of drilling a hole so that the screw head lies beneath the wood surface when inserted; usually concealed with a matching wood plug.

Countersinking The process of enlarging a clearance hole opening to accept the countersunk screw head.

Countersunk Refers to the underside of the head of a wood screw, which is bevelled to sit inside a corresponding recess in the timber. Phillips A screw pattern with a cross-headed slot.

Pozidriv A screw pattern with a cross-headed slot, plus additional shallow grooves.

Torque The twisting force when driving a screw; measured in Nm with power tools.

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