Screw applications made simple

Press, 27 July 1989, Page 25

Screw applications made simple

BUILDING

Everyone is familiar with wood screws. Many types have been developed in recent times in response to today’s new materials. Wood screws The wellknown wood screw with the slotted head is made with either a countersunk, round or raised head and is available in plain steel, zinc or bronze coated and brass. Much greater care

Much greater care should be taken with brass screws. Brass is a much softer metal than steel, so a larger pilot hole should be drilled so that no strain will be placed on the screw during insertion. A lubricant coating — soap, tallow, beeswax or lanolin will assist the easy insertion of the screw, especially in hard wood, without any loss of holding power.

Conventional wood screws come in lengths of 3/8 inch — three inches and in 10 gauges. It is necessary to drill a pilot hole for these wood screws. If you wish the screw head to be level with the surface of the top of the pilot hole, it should be enlarged to accommodate the countersunk shape. The secret of withdrawing slotted head screws successfully is to use the right size screw driver. If the screw head is filled with paint, chip it out completely first, then make sure the blade you are using fits firmly inside the screw slot. Twinfast screws with pozidrive head. The manufacturers claim this to be the most advanced

screw obtainable. Its characteristics are: faster and truer driving, no splitting and more grip. They are ideal for using with customwood and softer materials. Parallel twin threads provide almost twice the thread pitch as ordinary wood screws. Fewer turns are required, resulting in faster production, less fatigue and lower assembly costs. It has greater holding power.

The self-centring point gives balanced driving — the screw starts straight and drives true.

Cylindrical construction results in a parallel diameter, eliminating the tendency to split timber which often happens with ordinary wood screws because of their wedge shaped core. The relieved shank diameter — where screws are not threaded up to the head the unthreaded shank has a smaller diameter than the thread. This stops the stripping of the hole and helps to reduce splitting. The new head design can be driven with an electric drill attachment.

Twinfast pozidrive screws come mainly in zinc and bronze coated finishes and from % inch

— two inches and seven gauges.

The Surefast or Super Screw is an even newer design. They are specially hardened, self-counter-sinking and selfdrilling. For applications where pilot holes are undesirable and high clamp loads are required — for clamping, glued joints, fixing wall brackets and wall furnishings to walls, they are ideal. A new modification now on the market is a super screw of normal diameter with a countersunk head to fit hinges. It is particularly suitable for use with an electric drill and pozidrive attachment.